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Monarch butterfly

February 15, 2024

The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae.[6] Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown.[7] It is amongst the most familiar of North American butterflies and an iconic pollinator,[8] although it is not an especially effective pollinator of milkweeds.[9][10] Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9–10.2 cm (3.5–4.0 in).[11] A Müllerian mimic, the viceroy butterfly, is similar in color and pattern, but is markedly smaller and has an extra black stripe across each hindwing.

Monarch butterfly
Male
Female

Least Concern (IUCN 3.1)[1] (entire species)

Vulnerable (IUCN 3.1)[2] (migratory subspecies)
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Nymphalidae
Genus: Danaus
Species:
D. plexippus
Binomial name
Danaus plexippus
Synonyms
  • Papilio plexippus (Linnaeus, 1758)
  • Danaus archippus (Fabricius, 1793)[3]
  • Danaus menippe (Hübner, 1816)[4]
  • Anosia plexippus (Moore, 1883)[5]
D. p. plexippus
Piedra Herrada, Mexico

The eastern North American monarch population is notable for its annual southward late-summer/autumn instinctive migration from the northern and central United States and southern Canada to Florida and Mexico.[6] During the fall migration, monarchs cover thousands of miles, with a corresponding multigenerational return north in spring. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern California, but individuals have been found in overwintering Mexican sites, as well.[12][13] In 2009, monarchs were reared on the International Space Station, successfully emerging from pupae located in the station's Commercial Generic Bioprocessing Apparatus.[14][15]

Etymology edit

The name "monarch" is believed to have been given in honor of King William III of England, as the butterfly's main color is that of the king's secondary title, Prince of Orange.[16] The monarch was originally described by Carl Linnaeus in his Systema Naturae of 1758 and placed in the genus Papilio.[17] In 1780, Jan Krzysztof Kluk used the monarch as the type species for a new genus, Danaus. Although works published between at least 1883 and 1944 identified the species as Anosia plexippus,[18] the genus name was merged into Danaus in 2005.[19]

Danaus (Ancient Greek Δαναός), a great-grandson of Zeus, was a mythical king in Egypt or Libya, who founded Argos; Plexippus (Πλήξιππος) was one of the 50 sons of Aegyptus, the twin brother of Danaus. In Homeric Greek, his name means "one who urges on horses", i.e., "rider" or "charioteer".[20] In the tenth edition of Systema Naturae, at the bottom of page 467,[21] Linnaeus wrote that the names of the Danai festivi, the division of the genus to which Papilio plexippus belonged, were derived from the sons of Aegyptus. Linnaeus divided his large genus Papilio, containing all known butterfly species, into what we would now call subgenera. The Danai festivi formed one of the "subgenera", containing colorful species, as opposed to the Danai candidi, containing species with bright white wings. Linnaeus wrote: "Danaorum Candidorum nomina a filiabus Danai Aegypti, Festivorum a filiis mutuatus sunt." (English: "The names of the Danai candidi have been derived from the daughters of Danaus, those of the Danai festivi from the sons of Aegyptus.").

Robert Michael Pyle suggested Danaus is a masculinized version of Danaë (Greek Δανάη), Danaus's great-great-granddaughter, to whom Zeus came as a shower of gold, which seemed to him a more appropriate source for the name of this butterfly.[22]

Taxonomy edit

 
White morph of the monarch in Hawaii called the white monarch
Monarch butterfly, Ashbury, Sydney, 2023

Monarchs belong in the subfamily Danainae of the family Nymphalidae. Danainae was formerly considered a separately family Danaidae.[23] The three species of monarch butterflies are:

  • D. plexippus, described by Linnaeus in 1758, is the species known most commonly as the monarch butterfly of North America. Its range actually extends worldwide, including Hawaii, Australia, New Zealand, Spain, and the Pacific Islands.
  • D. erippus, the southern monarch, was described by Pieter Cramer in 1775. This species is found in tropical and subtropical latitudes of South America, mainly in Brazil, Uruguay, Paraguay, Argentina, Bolivia, Chile, and southern Peru. The South American monarch and the North American monarch may have been one species at one time. Some researchers believe the southern monarch separated from the monarch's population some two million years ago, at the end of the Pliocene. Sea levels were higher, and the entire Amazonas lowland was a vast expanse of brackish swamp that offered limited butterfly habitat.[19]
  • D. cleophile, the Jamaican monarch, described by Jean-Baptiste Godart in 1819, ranges from Jamaica to Hispaniola.[2]

Six subspecies and two color morphs of D. plexippus have been identified:[7]

  • D. p. plexippus – nominate subspecies, described by Linnaeus in 1758, is the migratory subspecies known from most of North America.
    • D. p. p. "form nivosus", the white monarch commonly found on Oahu, Hawaii, and rarely in other locations.[24]
    • D. p. p. (as yet unnamed) – a color morph lacking some wing vein markings.[25]
  • D. p. nigrippus (Richard Haensch, 1909) – South America - as forma: Danais [sic] archippus f. nigrippus. Hay-Roe et al. in 2007 identified this taxon as a subspecies[26]
  • D. p. megalippe (Jacob Hübner, [1826]) – nonmigratory subspecies, and is found from Florida and Georgia southwards, throughout the Caribbean and Central America to the Amazon River.
  • D. p. leucogyne (Arthur G. Butler, 1884) − St. Thomas
  • D. p. portoricensis Austin Hobart Clark, 1941 − Puerto Rico
  • D. p. tobagi Austin Hobart Clark, 1941 − Tobago

The population level of the white morph in Oahu is nearing 10%. On other Hawaiian islands, the white morph occurs at a relatively low frequency. White monarchs (D. p. p. "form nivosus") have been found throughout the world, including Australia, New Zealand, Indonesia, and the United States.[24] However, some taxonomists disagree on these classifications.[19][26]

Genome edit

The monarch was the first butterfly to have its genome sequenced.[27]: 12  The 273-million-base pair draft sequence includes a set of 16,866 protein-coding genes. The genome provides researchers insights into migratory behavior, the circadian clock, juvenile hormone pathways, and microRNAs that are differentially expressed between summer and migratory monarchs.[28][29][30] More recently, the genetic basis of monarch migration and warning coloration has been described.[31]

No genetic differentiation exists between the migratory populations of eastern and western North America.[27]: 16  Recent research has identified the specific areas in the genome of the monarch that regulate migration. No genetic difference is seen between a migrating and nonmigrating monarch, but the gene is expressed in migrating monarchs, but not expressed in nonmigrating monarchs.[32]

A 2015 publication identified genes from wasp bracoviruses in the genome of the North American monarch[33] leading to articles about monarch butterflies being genetically modified organisms.[34][35]

Life cycle edit

 
The life cycle of the monarch butterfly

Like all Lepidoptera, monarchs undergo complete metamorphosis; their life cycle has four phases: egg, larva, pupa, and adult. Monarchs transition from eggs to adults during warm summer temperatures in as little as 25 days, extending to as many as seven weeks during cool spring conditions. During their development, both larvae and their milkweed hosts are vulnerable to weather extremes, predators, parasites, and diseases; commonly fewer than 10% of monarch eggs and caterpillars survive.[27]: 21–22 

Egg edit

 
Egg

The egg is derived from materials ingested as a larva and from the spermatophores received from males during mating.[36] Female monarchs lay eggs singly, most often on the underside of a young leaf of a milkweed plant during the spring and summer.[37] Females secrete a small amount of glue to attach their eggs directly to the plant. They typically lay 300 to 500 eggs over a two- to five-week period.[38]

Eggs are cream colored or light green, ovate to conical in shape, and about 1.2 mm × 0.9 mm (0.047 in × 0.035 in) in size. The eggs weigh less than 0.5 mg (0.0077 gr) each and have raised ridges that form longitudinally from the point to apex to the base. Although each egg is 1⁄1000 the mass of the female, she may lay up to her own mass in eggs. Females lay smaller eggs as they age. Larger females lay larger eggs.[36] The number of eggs laid by a female, which may mate several times, can reach 1,180.[39]

Eggs take three to eight days to develop and hatch into larvae or caterpillars.[27]: 21  The offspring's consumption of milkweed benefits health and helps defend them against predators.[40][41] Monarchs lay eggs along the southern migration route.[42]

Larva edit

 
Size comparison between a black swallowtail caterpillar (top), a monarch caterpillar (middle), and a queen caterpillar (bottom) all on a human hand

The larva (caterpillar) has five stages (instars), molting at the end of each instar. Instars last about 3 to 5 days, depending on factors such as temperature and food availability.[6][43]

The first-instar caterpillar that emerges from the egg is pale green or grayish-white, shiny, and almost translucent, with a large, black head. It lacks banding coloration or tentacles. The larvae or caterpillar eats its egg case and begins to feed on milkweed with a circular motion, often leaving a characteristic, arc-shaped hole in the leaf. Older first-instar larvae have dark stripes on a greenish background and develop small bumps that later become front tentacles. The first instar is usually between 2 and 6 mm (0.079 and 0.236 in) long.[43]

The second-instar larva develops a characteristic pattern of white, yellow, and black transverse bands. The larva has a yellow triangle on the head and two sets of yellow bands around this central triangle. It is no longer translucent, and is covered in short setae. Pairs of black tentacles begin to grow, a larger pair on the thorax and a smaller pair on the abdomen. The second instar is usually between 6 mm (0.24 in) and 1 cm (0.39 in) long.[43]

Fifth-instar monarch larva eating milkweed leaves (Some at 20 × speed). A second-instar larva grazing on leaf and cutting through a latex vein.

The fourth-instar larva has a different banding pattern. It develops white spots on the prolegs near its back, and is usually between 1.5 and 2.5 cm (0.59 and 0.98 in) long.[43] The third-instar larva has more distinct bands and the two pairs of tentacles become longer. Legs on the thorax differentiate into a smaller pair near the head and larger pairs further back. Third-instar larvae usually feed using a cutting motion on leaf edges. The third instar is usually between 1 and 1.5 cm (0.39 and 0.59 in) long.[43]

 
A monarch caterpillar on milkweed

The fifth-instar larva has a more complex banding pattern and white dots on the prolegs, with front legs that are small and very close to the head. Its length ranges from 2.5 to 4.5 cm (0.98 to 1.77 in).[6][43] The larvae typically chew through a latex vein to relieve the pressure and feed above it. Fifth-instar larvae often chew a notch in the  petiole  of the leaf they are eating, which relieves the latex pressure and causes the leaf to fall into a vertical position.

As the caterpillar completes its growth, it is 4.5 cm (1.8 in) long (large specimens can reach 5 cm (2.0 in)) and 7 to 8 mm (0.28 to 0.31 in) wide, and weighs about 1.5 g (0.053 oz), compared to the first instar, which is 2 to 6 mm (0.079 to 0.236 in) long and 0.5 to 1.5 mm (0.020 to 0.059 in) wide. Fifth-instar larvae greatly increase in size and weight. They then stop feeding and are often found far from milkweed plants as they seek a site for pupating.[43]

In a laboratory setting, the fourth- and fifth-instar stages of the caterpillar showed signs of aggressive behavior with lower food availability. Attacked caterpillars were found to be attacked when it was feeding on milkweed leaves, and the caterpillars attacked when foraging for milkweed.[44] This demonstrates the aggressive behavior of monarch caterpillars due to the availability of milkweed.

Pupa edit

 
Chrysalis

To prepare for the pupal or chrysalis stage, the caterpillar chooses a safe place for pupation, where it spins a silk pad on a downward-facing horizontal surface. At this point, it turns around and securely latches on with its last pair of hind legs and hangs upside down, in the form of the letter J. After "J-hanging" for about 12–16 hours, it soon straightens out its body and goes into peristalsis some seconds before its skin splits behind its head. It then sheds its skin over a period of a few minutes, revealing a green chrysalis. At first, the chrysalis is long, soft, and somewhat amorphous, but over a few hours, it compacts into its distinct shape – an opaque, pale-green chrysalis with small golden dots near the bottom, and a gold-and-black rim around the dorsal side near the top.[45] At first, its exoskeleton is soft and fragile, but it hardens and becomes more durable within about a day. At this point, it is about 2.5 cm (0.98 in) long and 10–12 mm (0.39–0.47 in) wide, weighing about 1.2 g (0.042 oz). At normal summer temperatures, it matures in 8–15 days (usually 11–12 days). During this pupal stage, the adult butterfly forms inside. A day or so before emerging, the exoskeleton first becomes translucent and the chrysalis more bluish. Finally, within 12 hours or so, it becomes transparent, revealing the black and orange colors of the butterfly inside before it ecloses (emerges).[46][47]

Adult edit

 
An emergent monarch clinging to its chrysalis shell

The adult emerges from its chrysalis after about two weeks of pupation. The emergent adult hangs upside down for several hours while it pumps fluids and air into its wings, which expand, dry, and stiffen. The butterfly then extends and retracts its wings. Once conditions allow, it flies and feeds on a variety of nectar plants. During the breeding season, adults reach sexual maturity in 4–5 days. However, the migrating generation does not reach maturity until overwintering is complete.[48]

Monarch butterflies flying and sipping nectar from milkweed flowers

The adult's wingspan ranges from 8.9 to 10.2 centimetres (3.5 to 4.0 in).[11] The upper sides of the wings are tawny orange, the veins and margins are black, and two series of small white spots occur in the margins. Monarch forewings also have a few orange spots near their tips. Wing undersides are similar, but the tips of forewings and hindwings are yellow brown instead of tawny orange and the white spots are larger.[49] The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants.[50] Wings size and shape differ between migratory and nonmigratory monarchs. Monarchs from eastern North America have larger and more angular forewings than those in the western population.[27]

In eastern North American populations, overall wing size in the physical dimensions of wings varies. Males tend to have larger wings than females, and are typically heavier than females. Both males and females have similar thoracic dimensions. Female monarchs tended to have thicker wings, which is thought to convey greater tensile strength and reduce the likelihood of being damaged during migration. Additionally, females had lower wing loading than males, which would mean females require less energy to fly.[51]

Adults are sexually dimorphic. Males are slightly larger than females and have a black spot on a vein on each hindwing. The spots contain scales that produce pheromones that many Lepidoptera use during courtship. Females are often darker than males and have wider veins on their wings. The ends of the abdomens of males and females differ in shape.[49][52][27][53][54][55]

The adult's thorax has six legs, but as in all of the Nymphalidae, the forelegs are small and held against the body. The butterfly uses only its middle and hindlegs when walking and clinging.[56]

Adults typically live for 2–5 weeks during their breeding season.[27]: 22–23  Larvae growing in high densities are smaller, have lower survival, and weigh less as adults compared with those growing in lower densities.[57]

Vision edit

Physiological experiments suggest that monarch butterflies view the world through a tetrachromatic system.[58] Like humans, their retina contain three types of opsin proteins, expressed in distinct photoreceptor cells, each of which absorbs light at a different wavelength. Unlike humans, one of those types of photoreceptor cells corresponds to a wavelength in the ultraviolet range; the other two correspond to blue and green.[59]

In addition to these three photoreceptors cells in the main retina, monarch butterfly eyes contain orange filtering pigments that filter the light reaching some green-absorbing opsins, thereby making a fourth photoreceptor cell sensitive to longer-wavelength light.[58] The combination of filtered and unfiltered green opsins permits the butterflies to distinguish yellow from orange colors.[58] The ultraviolet opsin protein has also been detected in the dorsal rim region of monarch eyes. One study suggests that this allows the butterflies the ability to detect ultraviolet polarized skylight to orient themselves with the sun for their long migratory flight.[60]

These butterflies are capable of distinguishing colors based on their wavelength only, and not based on intensity; this phenomenon is termed "true color vision". This is important for many butterfly behaviors, including seeking nectar for nourishment, choosing a mate, and finding milkweed on which to lay eggs. One study found that floral color is more easily recognized at a distance by butterflies searching for nectar than floral shape. This may be because flowers have highly contrasting colors to the green background of a vegetative landscape.[61] On the other hand, leaf shape is important for oviposition so that the butterflies can ensure their eggs are being laid on milkweed.

Beyond the perception of color, the ability to remember certain colors is essential in the life of monarch butterflies. These insects can easily learn to associate color, and to a lesser extent, shape, with sugary food rewards. When searching for nectar, color is the first cue that draws the insect's attention toward a potential food source, and shape is a secondary characteristic that promotes the process. When searching for a place to lay its eggs, the roles of color and shape are switched. Also, a difference may exist between male and female butterflies from other species in terms of the ability to learn certain colors; however, no differences are noted between the sexes for monarch butterflies.[61]

Courtship and mating edit

Monarch butterflies mating (video)

Monarch courtship occurs in two phases. During the aerial phase, a male pursues and often forces a female to the ground. During the ground phase, the butterflies copulate and remain attached for about 30 to 60 minutes.[62] Only 30% of mating attempts end in copulation, suggesting that females may be able to avoid mating, though some have more success than others.[63][64] During copulation, a male transfers his spermatophore to a female. Along with sperm, the spermatophore provides a female with nutrition, which aids her in laying eggs. An increase in spermatophore size increases the fecundity of female monarchs. Males that produce larger spermatophores also fertilize more females' eggs.[65]

Females and males typically mate more than once. Females that mate several times lay more eggs.[66] Mating for the overwintering populations occurs in the spring, prior to dispersion. Mating is less dependent on pheromones than in other species in its genus.[67] Male search and capture strategies may influence copulatory success, and human-induced changes to the habitat can influence monarch mating activity at overwintering sites.[68]

Distribution and habitat edit

 
String of monarchs wintering at California's Pismo State Beach Monarch Preserve (2015)

The range of the western and eastern populations of D. p. plexippus expands and contracts depending upon the season. The range differs between breeding areas, migration routes, and winter roosts.[27]: 18  However, no genetic differences between the western and eastern monarch populations exist;[32] reproductive isolation has not led to subspeciation of these populations, as it has elsewhere within the species' range.[27]: 19 

In the Americas, the monarch ranges from southern Canada through northern South America.[6] It is also found in Bermuda, the Cook Islands,[69] Hawaii,[70][71] Cuba,[72] and other Caribbean islands,[27]: 18  the Solomons, New Caledonia, New Zealand,[73] Papua New Guinea,[74] Australia, the Azores, the Canary Islands, Madeira, continental Portugal, Gibraltar,[75] the Philippines, and Morocco.[76] It appears in the UK in some years as an accidental migrant.[77]

Overwintering populations of D. p. plexippus are found in Mexico, California, along the Gulf Coast of the United States, year-round in Florida, and in Arizona where the habitat has the specific conditions necessary for their survival.[78][79] On the East Coast of the United States, they have overwintered as far north as Lago Mar, Virginia Beach, Virginia.[80] Their wintering habitat typically provides access to streams, plenty of sunlight (enabling body temperatures that allow flight), and appropriate roosting vegetation, and is relatively free of predators.

Overwintering, roosting butterflies have been seen on basswoods, elms, sumacs, locusts, oaks, osage-oranges, mulberries, pecans, willows, cottonwoods, and mesquites.[81] While breeding, monarch habitats can be found in agricultural fields, pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides – anywhere there is access to larval host plants.[82]

Larval host plants edit

The host plants used by the monarch caterpillar include:

 
Inflorescence of swamp milkweed, one of many species of Asclepias milkweeds that serve as hosts for monarch caterpillars

Asclepias curassavica, or tropical milkweed, is often planted as an ornamental in butterfly gardens. Year-round plantings in the USA are controversial and criticised, as they may be the cause of new overwintering sites along the U.S. Gulf Coast, leading to year-round breeding of monarchs.[102] This is thought to adversely affect migration patterns, and to cause a dramatic buildup of the dangerous parasite, Ophryocystis elektroscirrha.[103] New research also has shown that monarch larvae reared on tropical milkweed show reduced migratory development (reproductive diapause), and when migratory adults are exposed to tropical milkweed, it stimulates reproductive tissue growth.[104]

Adult food sources edit

 
Nectaring on purple coneflower (Echinacea purpurea)

Although larvae eat only milkweed, adult monarchs feed on the nectar of many plants, including:[105]

Monarchs obtain moisture and minerals from damp soil and wet gravel, a behavior known as mud-puddling. The monarch has also been noticed puddling at an oil stain on pavement.[79]

Flight and migration edit

 
Overwintering on Oyamel fir (Abies religiosa)
Piedra Herrada, Mexico
Further information: Monarch butterfly migration
 
Migrating monarchs resting on a pine tree in Fire Island National Seashore on Fire Island, New York (September 2021)

In North America, monarchs migrate both north and south on an annual basis, making long-distance journeys that are fraught with risks.[6] This is a multi-generational migration, with individual monarchs only making part of the full journey.[107] The population east of the Rocky Mountains attempts to migrate to the sanctuaries of the Mariposa Monarca Biosphere Reserve in the Mexican state of Michoacán and parts of Florida. The western population tries to reach overwintering destinations in various coastal sites in central and southern California. The overwintered population of those east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration. The second, third, and fourth generations return to their northern locations in the United States and Canada in the spring.[108]

Captive-raised monarchs appear capable of migrating to overwintering sites in Mexico,[109] though they have a much lower migratory success rate than do wild monarchs (see section on captive-rearing below).[110] Monarch overwintering sites have been discovered recently in Arizona.[111] Monarchs from the eastern US generally migrate longer distances than monarchs from the western US.[112]

Since the 1800s, monarchs have spread throughout the world, and there are now many non-migratory populations globally.[113]

Flight speeds of adults are around 9 km/h (6 mph).[114]

Interactions with predators edit

In both caterpillar and butterfly form, monarchs are aposematic, warding off predators with a bright display of contrasting colors to warn potential predators of their undesirable taste and poisonous characteristics. One monarch researcher emphasizes that predation on eggs, larvae or adults is natural, since monarchs are part of the food chain, thus people should not take steps to kill predators of monarchs.[115]

Larvae feed exclusively on milkweed and consume protective cardiac glycosides. Toxin levels in Asclepias species vary. Not all monarchs are unpalatable, but exhibit Batesian or automimics. Cardiac glycosides levels are higher in the abdomen and wings. Some predators can differentiate between these parts and consume the most palatable ones.[116]

Butterfly weed (A. tuberosa) lacks significant amounts of cardiac glycosides (cardenolides), but instead contains other types of toxic glycosides, including pregnanes.[117][118][119] This difference may reduce the toxicity of monarchs whose larvae feed on that milkweed species and affect the butterfly's breeding choices, as a naturalist and others have reported that egg-laying monarchs do not favor the plant.[120] Some other milkweeds have similar characteristics.[121]

Types of predators edit

While monarchs have a wide range of natural predators, none of these is suspected of causing harm to the overall population, or are the cause of the long-term declines in winter colony sizes.

Several species of birds have acquired methods that allow them to ingest monarchs without experiencing the ill effects associated with the cardiac glycosides (cardenolides). The black-backed oriole is able to eat the monarch through an exaptation of its feeding behavior that gives it the ability to identify cardenolides by taste and reject them.[122] The black-headed grosbeak, though, has developed an insensitivity to secondary plant poisons that allows it to ingest monarchs without vomiting.[123] As a result, these orioles and grosbeaks periodically have high levels of cardenolides in their bodies, and they are forced to go on periods of reduced monarch consumption. This cycle effectively reduces potential predation of monarchs by 50% and indicates that monarch aposematism has a legitimate purpose.[122] The black-headed grosbeak has also evolved resistance mutations in the molecular target of the heart poisons, the sodium pump. The specific mutations that evolved in one of the grosbeak's four copies of the sodium pump gene are the same as those found in some rodents that have also evolved to resist cardiac glycosides.[124] Known bird predators include brown thrashers, grackles, robins, cardinals, sparrows, scrub jays, and pinyon jays.[116]

The monarch's white morph appeared in Oahu after the 1965–1966 introduction of two bulbul bird species, Pycnonotus cafer and Pycnonotus jocosus. These are now the most common avian insectivores in Hawaii, and probably the only ones that eat insects as large as monarchs. Although Hawaiian monarchs have low cardiac glycoside levels, the birds may also be tolerant of that toxin. The two species hunt the larvae and some pupae from the branches and undersides of leaves in milkweed bushes. The bulbuls also eat resting and ovipositing adults, but rarely flying ones. Because of its color, the white morph has a higher survival rate than the orange one. This is either because of apostatic selection (i.e., the birds have learned the orange monarchs can be eaten), because of camouflage (the white morph matches the white pubescence of milkweed or the patches of light shining through foliage), or because the white morph does not fit the bird's search image of a typical monarch, so is thus avoided.[125]

1) A stink (shield) bug killing and consuming a fourth-instar monarch larva. 2) A mature fifth instar larva jerking to dislodge a large milkweed bug (a herbivore). 3) A fourth-instar larva killed by insect parasitoids, non-insect parasites or a pathogen.

Some mice, particularly the black-eared mouse (Peromyscus melanotis), are, like all rodents, able to tolerate large doses of cardenolides and are able to eat monarchs.[126] Overwintering adults become less toxic over time making them more vulnerable to predators. In Mexico, about 14% of the overwintering monarchs are eaten by birds and mice and black-eared mice can eat up to 40 monarchs per night.[78][126]

In North America, eggs and first-instar larvae of the monarch are eaten by larvae and adults of the introduced Asian lady beetle (Harmonia axyridis).[127] The Chinese mantis (Tenodera sinensis) will consume the larvae once the gut is removed thus avoiding cardenolides.[128] Predatory wasps commonly consume larvae.[129] Many Hemipteran bugs including predatory stink bugs in the subfamily Asopinae and assassin bugs in family Reduviidae eat monarchs. Larvae can sometimes avoid predation by dropping from the plant or by jerking their bodies.[130]

Parasitoids, including tachinid flies and braconid wasps develop inside the monarch larvae eventually killing it and emerging from the larvae or pupa. Non-insect parasites and infectious diseases (pathogens) also kill monarchs.

Aposematism edit

 
Chemical structure of oleandrin, one of the cardiac glycosides

Monarchs are toxic and foul-tasting because of the presence of cardenolides in their bodies, which the caterpillars ingest as they feed on milkweed.[67] Monarchs and other cardenolide-resistant insects rely on a resistant form of the Na+/ K+-ATPase enzyme to tolerate significantly higher concentrations of cardenolides than nonresistant species.[131] By ingesting a large amount of plants in the genus Asclepias, primarily milkweed, monarch caterpillars are able to sequester cardiac glycosides, or more specifically cardenolides, which are steroids that act in heart-arresting ways similar to digitalis.[132] It has been found that monarchs are able to sequester cardenolides most effectively from plants of intermediate cardenolide content rather than those of high or low content.[133] Three mutations that evolved in the monarch's Na+/ K+-ATPase were found to be sufficient together to confer resistance to dietary cardiac glycosides.[131] This was tested by swapping these mutations into the same gene in the fruit fly Drosophila melanogaster using CRISPR-Cas9 genome editing. These fruit flies-turned monarch flies[134] were completely resistant to dietary ouabain, a cardiac glycoside found in Apocynaceae, and even sequestered some through metamorphosis, like the monarch.[131]

Different species of milkweed have different effects on growth, virulence, and transmission of parasites.[135] One species, Asclepias curassavica, appears to reduce the symptoms of Ophryocystis elektroscirrha (OE) infection. The two possible explanations for this include that it promotes overall monarch health to boost the monarch's immune system or that chemicals from the plant have a direct negative effect on the OE parasites.[135] A. curassavica does not cure or prevent the infection with OE; it merely allows infected monarchs to live longer, and this would allow infected monarchs to spread the OE spores for longer periods. For the average home butterfly garden, this scenario only adds more OE to the local population.[136]

After the caterpillar becomes a butterfly, the toxins shift to different parts of the body. Since many birds attack the wings of the butterfly, having three times the cardiac glycosides in the wings leaves predators with a very foul taste and may prevent them from ever ingesting the body of the butterfly.[132] To combat predators that remove the wings only to ingest the abdomen, monarchs keep the most potent cardiac glycosides in their abdomens.[137]

Mimicry edit

 
Monarch (left) and viceroy (right) butterflies exhibiting Müllerian mimicry

Monarchs share the defense of noxious taste with the similar-appearing viceroy butterfly in what is perhaps one of the most well-known examples of mimicry. Though long purported to be an example of Batesian mimicry, the viceroy is actually more unpalatable than the monarch, making this a case of Müllerian mimicry.[138]

Human interaction edit

The monarch is the state insect of Alabama,[139] Idaho,[140] Illinois,[141] Minnesota,[142] Texas,[143] Vermont,[144] and West Virginia.[145] Legislation was introduced to make it the national insect of the United States,[146] but this failed in 1989[147] and again in 1991.[148]

Homeowners are increasingly establishing butterfly gardens; monarchs can be attracted by cultivating a butterfly garden with specific milkweed species and nectar plants. Efforts are underway to establish these monarch waystations. [149]

An IMAX film, Flight of the Butterflies, describes the story of the Urquharts, Brugger, and Trail to document the then-unknown monarch migration to Mexican overwintering areas.[150]

Sanctuaries and reserves have been created at overwintering locations in Mexico and California to limit habitat destruction. These sites can generate significant tourism revenue.[151] However, with less tourism, monarch butterflies will have a higher survival rate because they show more protein content and a higher value of immune response and oxidative defense.[152]

Organizations and individuals participate in tagging programs. Tagging information is used to study migration patterns.[153]

The 2012 novel by Barbara Kingsolver, Flight Behavior, deals with the fictional appearance of a large population in the Appalachians.[154]

Captive rearing edit

Humans interact with monarchs when rearing them in captivity, which has become increasingly popular. However, risks occur in this controversial activity. On one hand, captive rearing has many positive aspects. Monarchs are bred in schools and used for butterfly releases at hospices, memorial events, and weddings.[155] Memorial services for the September 11 attacks include the release of captive-bred monarchs.[156][157][158] Monarchs are used in schools and nature centers for educational purposes.[159] Many homeowners raise monarchs in captivity as a hobby and for educational purposes.[160]

On the other hand, this practice becomes problematic when monarchs are "mass-reared". Stories in the Huffington Post in 2015 and Discover magazine in 2016 have summarized the controversy around this issue.[161][162]

The frequent media reports of monarch declines have encouraged many homeowners to attempt to rear as many monarchs as possible in their homes and then release them to the wild in an effort to "boost the monarch population". Some individuals, such as one in Linn County, Iowa, have reared thousands of monarchs at the same time.[163]

Some monarch scientists do not condone the practice of rearing "large" numbers of monarchs in captivity for release into the wild because of the risks of genetic issues and disease spread.[164] One of the biggest concerns of mass rearing is the potential for spreading the monarch parasite, Ophryocystis elektroscirrha, into the wild. This parasite can rapidly build up in captive monarchs, especially if they are housed together. The spores of the parasite also can quickly contaminate all housing equipment, so that all subsequent monarchs reared in the same containers then become infected. One researcher stated that rearing more than 100 monarchs constitutes "mass rearing" and should not be done.[165]

In addition to the disease risks, researchers believe these captive-reared monarchs are not as fit as wild ones, owing to the unnatural conditions in which they are raised. Homeowners often raise monarchs in plastic or glass containers in their kitchens, basements, porches, etc., and under artificial lighting and controlled temperatures. Such conditions would not mimic what the monarchs are used to in the wild, and may result in adults that are unsuited for the realities of their wild existence. In support of this, a recent study by a citizen scientist found that captive-reared monarchs have a lower migration success rate than wild monarchs do.[110]

A 2019 study shed light on the fitness of captive-reared monarchs, by testing reared and wild monarchs on a tethered flight apparatus that assessed navigational ability.[166] In that study, monarchs that were reared to adulthood in artificial conditions showed a reduction in navigational ability. This happened even with monarchs that were brought into captivity from the wild for a few days. A few captive-reared monarchs did show proper navigation. This study revealed the fragility of monarch development; if the conditions are not suitable, their ability to properly migrate could be impaired. The same study also examined the genetics of a collection of reared monarchs purchased from a butterfly breeder, and found they were dramatically different from wild monarchs, so much so that the lead author described them as "franken-monarchs".[167]

An unpublished study in 2019 compared behavior of captive-reared versus wild monarch larvae.[168] The study showed that reared larvae exhibited more defensive behavior than wild larvae. The reason for this is unknown, but it could relate to the fact that reared larvae are frequently handled and/or disturbed.

Threats edit

In February 2015, the U.S. Fish and Wildlife Service reported a study that showed that nearly a billion monarchs had vanished from the butterfly's overwintering sites since 1990. The agency attributed the monarch's decline in part to a loss of milkweed caused by herbicides that farmers and homeowners had used.[169]

Western monarch populations edit

See also: Threats to monarch butterfly in California
 
Western monarch populations from 1997 to 2013 (from Xerces Society data)

Based on a 2014 20-year comparison, the overwintering numbers west of the Rocky Mountains have dropped more than 50% since 1997 and the overwintering numbers east of the Rockies have declined by more than 90% since 1995. According to the Xerces Society, the monarch population in California decreased 86% in 2018, going from millions of butterflies to tens of thousands of butterflies.[170]

The society's annual 2020–2021 winter count showed a significant decline in the California population. One Pacific Grove site did not have a single monarch butterfly. A primary explanation for this was the destruction of the butterfly's milkweed habitats.[27][171] This particular population is believed to comprise less than 2000 individuals, as of 2022.[172]

Eastern and midwestern monarch populations edit

 
Area covered by monarchs (D. plexippus, eastern migratory population) in their overwintering areas in Mexico between 1993 and 2018

A 2016 publication attributed the previous decade's 90% decline in overwintering numbers of the eastern monarch population to the loss of breeding habitat and milkweed. The publication's authors stated that an 11%–57% probability existed that this population will go almost extinct over the next 20 years.[173]

Chip Taylor, the director of Monarch Watch at the University of Kansas, has stated that the Midwest milkweed habitat "is virtually gone" with 120–150 million acres lost.[174][175] To help fight this problem, Monarch Watch encourages the planting of "Monarch Waystations".[160]

Habitat loss due to herbicide use and genetically modified crops edit

Declines in milkweed abundance and monarch populations between 1999 and 2010 are correlated with the adoption of herbicide-tolerant genetically modified (GM) corn and soybeans, which now constitute 89% and 94% of these crops, respectively, in the U.S.[173] GM corn and soybeans are resistant to the effect of the herbicide glyphosate. Some conservationists attribute the disappearance of milkweed to agricultural practices in the Midwest, where GM seeds are bred to resist herbicides that farmers use to kill unwanted plants that grow near their rows of food crops.[176][177]

In 2015, the Natural Resources Defense Council filed a suit against the United States Environmental Protection Agency (EPA). The Council argued that the agency ignored warnings about the dangers of glyphosate usage for monarchs.[178] However, a 2018 study has suggested that the decline in milkweed predates the arrival of GM crops.[179]

Losses during migration edit

 
Monarch nectaring on a zinnia flower during its migration southward to Mexico, late September of 2022

Eastern and midwestern monarchs are apparently experiencing problems reaching Mexico. A number of monarch researchers have cited recent evidence obtained from long-term citizen science data that show that the number of breeding (adult) monarchs has not declined in the last two decades.[180][181][182]

The lack of long-term declines in the numbers of breeding and migratory monarchs, yet the clear declines in overwintering numbers, suggests a growing disconnect exists between these life stages. One researcher has suggested that mortality from car strikes constitutes an increasing threat to migrating monarchs.[183] A study of road mortality in northern Mexico, published in 2019, showed very high mortality from just two "hotspots" each year, amounting to 200,000 monarchs killed.[184]

Loss of overwintering habitat edit

The area of Mexican forest to which eastern and midwestern monarchs migrate reached its lowest level in two decades in 2013. The decline was expected to increase during the 2013–2014 season. Mexican environmental authorities continue to monitor illegal logging of the oyamel trees. The oyamel is a major species of evergreen on which the overwintering butterflies spend a significant time during their winter diapause, or suspended development.[185]

A 2014 study acknowledged that while "the protection of overwintering habitat has no doubt gone a long way towards conserving monarchs that breed throughout eastern North America", their research indicates that habitat loss on breeding grounds in the United States is the main cause of both recent and projected population declines.[186]

Western monarch populations have rebounded slightly since 2014 with the Western Monarch Thanksgiving Count [187] tallying 335,479 monarchs in 2022. The population still has much to go for a full recovery.

Parasites edit

 
Pteromalus cassotis on monarch chrysalis

Parasites include the tachinid flies Sturmia convergens[188] and Lespesia archippivora. Lesperia-parasitized butterfly larvae suspend, but die prior to pupation. The fly's maggot lowers itself to the ground, forms a brown puparium and then emerges as an adult.[189]

Pteromalid wasps, specifically Pteromalus cassotis, parasitize monarch pupae.[190] These wasps lay their eggs in the pupae while the chrysalis is still soft. Up to 400 adults emerge from the chrysalis after 14–20 days,[190] killing the monarch.

The bacterium Micrococcus flacidifex danai also infects larvae. Just before pupation, the larvae migrate to a horizontal surface and die a few hours later, attached only by one pair of prolegs, with the thorax and abdomen hanging limp. The body turns black shortly thereafter. The bacterium Pseudomonas aeruginosa has no invasive powers, but causes secondary infections in weakened insects. It is a common cause of death in laboratory-reared insects.[189]

Ophryocystis elektroscirrha is another parasite of the monarch. It infects the subcutaneous tissues and propagates by spores formed during the pupal stage. The spores are found over all of the body of infected butterflies, with the greatest number on the abdomen. These spores are passed, from female to caterpillar, when spores rub off during egg laying and are then ingested by caterpillars. Severely infected individuals are weak, unable to expand their wings, or unable to eclose, and have shortened lifespans, but parasite levels vary in populations. This is not the case in laboratory rearing, where after a few generations, all individuals can be infected.[191]

Infection with O. elektroscirrha creates an effect known as culling, whereby migrating monarchs that are infected are less likely to complete the migration. This results in overwintering populations with lower parasite loads.[192] Owners of commercial butterfly-breeding operations claim that they take steps to control this parasite in their practices,[193] although this claim is doubted by many scientists who study monarchs.[194]

Confusion of host plants edit

The black swallow-wort (Cynanchum louiseae) and pale swallow-wort (Cynanchum rossicum) plants are problematic for monarchs in North America. Monarchs lay their eggs on these relatives of native vining milkweed (Cynanchum laeve) because they produce stimuli similar to milkweed. Once the eggs hatch, the caterpillars are poisoned by the toxicity of this invasive plant from Europe.[195]

Climate edit

Climate variations during the fall and summer affect butterfly reproduction. Rainfall and freezing temperatures affect milkweed growth. Omar Vidal, director general of WWF-Mexico, said, "The monarch's lifecycle depends on the climatic conditions in the places where they breed. Eggs, larvae, and pupae develop more quickly in milder conditions. Temperatures above 35 °C (95 °F) can be lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate."[196] If a monarch's body temperatures is below 30 °C (86 °F), a monarch cannot fly. To warm up, they sit in the sun or rapidly shiver their wings to warm themselves.[197]

Climate change may dramatically affect the monarch migration. A study from 2015 examined the impact of warming temperatures on the breeding range of the monarch, and showed that in the next 50 years the monarch host plant will expand its range further north into Canada, and that the monarchs will follow this.[198] While this will expand the breeding locations of the monarch, it will also have the effect of increasing the distance that monarchs must travel to reach their overwintering destination in Mexico, which could result in greater mortality during the migration.[199]

Milkweeds grown at increased temperatures have been shown to contain higher cardenolide concentrations, making the leaves too toxic for the monarch caterpillars. However, these increased concentrations are likely in response to increased insect herbivory, which is also caused by the increased temperatures. Whether increased temperatures make milkweed too toxic for monarch caterpillars when other factors are not present is unknown.[200] Additionally, milkweed grown at carbon dioxide levels of 760 parts per million was found to produce a different mix of the toxic cardenolides, one of which was less effective against monarch parasites.[201]

Conservation status edit

On July 20, 2022, the International Union for Conservation of Nature added the migratory monarch butterfly (the subspecies common in North America) to its red list of endangered species.[202][2]

The monarch butterfly is not currently listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora or protected specifically under U.S. domestic laws.[203]

On August 14, 2014, the Center for Biological Diversity and the Center for Food Safety filed a legal petition requesting Endangered Species Act protection for the monarch and its habitat,[27] based largely on the long-term trends observed at overwintering sites. The U.S. Fish and Wildlife Service (FWS) initiated a status review of the monarch butterfly under the Endangered Species Act with a due date for information submission of March 3, 2015, later extended to 2020. On December 15, 2020, the FWS ruled that adding the butterfly to the list of threatened and endangered species was "warranted-but-precluded" because it needed to devote its resources to 161 higher-priority species.[204]

The number of monarchs overwintering in Mexico has shown a long-term downward trend. Since 1995, coverage numbers have been as high as 18 hectares (44 acres) during the winter of 1996–1997, but on average about 6 hectares (15 acres). Coverage declined to its lowest point to date (0.67 hectares (1.66 acres)) during the winter of 2013–2014, but rebounded to 4.01 hectares (10 acres) in 2015–2016. The average population of monarchs in 2016 was estimated at 200 million. Historically, on average there are 300 million monarchs. The 2016 increase was attributed to favorable breeding conditions in the summer of 2015. However, coverage declined by 27% to 2.91 hectares (7.19 acres) during the winter of 2016–2017. Some believe this was because of a storm that had occurred during March 2016 in the monarchs' previous overwintering season,[205][206][207] though this seems unlikely since most current research shows that the overwintering colony sizes do not predict the size of the next summer breeding population.[208]

In Ontario, Canada, the monarch butterfly is listed as a species of special concern.[209] In fall 2016, the Committee on the Status of Endangered Wildlife in Canada proposed that the monarch be listed as endangered in Canada, as opposed to its current listing as a "species of concern" in that country. This move, once enacted, would protect critical monarch habitat in Canada, such as major fall accumulation areas in southern Ontario, but it would also have implications for citizen scientists who work with monarchs, and for classroom activities. If the monarch were federally protected in Canada, these activities could be limited, or require federal permits.[210]

In Nova Scotia, the monarch is listed as endangered at the provincial level, as of 2017. This decision (as well as the Ontario decision) apparently is based on a presumption that the overwintering colony declines in Mexico create declines in the breeding range in Canada.[211] Two recent studies have been conducted examining long-term trends in monarch abundance in Canada, using either butterfly atlas records[212] or citizen science butterfly surveys,[213] and neither shows evidence of a population decline in Canada.

Conservation efforts edit

See also: Monarch butterfly conservation in California

Although numbers of breeding monarchs in eastern North America have apparently not decreased, reports of declining numbers of overwintering butterflies have inspired efforts to conserve the species.[180][181][182]

Federal actions edit

On June 20, 2014, President Barack Obama issued a presidential memorandum entitled "Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators". The memorandum established a Pollinator Health Task Force, to be co-chaired by the Secretary of Agriculture and the Administrator of the Environmental Protection Agency, and stated:

The number of migrating Monarch butterflies sank to the lowest recorded population level in 2013–14, and there is an imminent risk of failed migration.[214]

In May 2015, the Pollinator Health Task Force issued a "National Strategy to Promote the Health of Honey Bees and Other Pollinators". The strategy laid out federal actions to achieve three goals, two of which were:

  • Monarch Butterflies: Increase the Eastern population of the monarch butterfly to 225 million butterflies occupying an area of approximately 15 acres (6 hectares) in the overwintering grounds in Mexico, through domestic/international actions and public-private partnerships, by 2020.
  • Pollinator Habitat Acreage: Restore or enhance 7 million acres of land for pollinators over the next 5 years through Federal actions and public/private partnerships.[215][216]

Many of the priority projects that the national strategy identified focused on the I-35 corridor, which extends for 1,500 miles (2,400 km) from Texas to Minnesota. The area through which that highway travels provides spring and summer breeding habitats in the United States' key monarch migration corridor.[215][216]

The Task Force simultaneously issued a "Pollinator Research Action Plan". The Plan outlined five main action areas, covered in ten subject-specific chapters. The action areas were: (1) Setting a Baseline; (2) Assessing Environmental Stressors; (3) Restoring Habitat; (4) Understanding and Supporting Stakeholders; (5) Curating and Sharing Knowledge.[216][217]

In June 2016, the Task Force issued a "Pollinator Partnership Action Plan". That Plan provided examples of past, ongoing, and possible future collaborations between the federal government and non-federal institutions to support pollinator health under each of the national strategy's goals.[218]

The U.S. General Services Administration (GSA) publishes sets of landscape performance requirements in its P100 documents, which mandate standards for the GSA's Public Buildings Service. Beginning in March 2015, those performance requirements and their updates have included four primary aspects for planting designs that are intended to provide adequate on-site foraging opportunities for targeted pollinators. The targeted pollinators include bees, butterflies, and other beneficial insects.[219]

On December 4, 2015, President Obama signed into law the Fixing America's Surface Transportation (FAST) Act (Pub. L. 114-94).[220] The FAST Act placed a new emphasis on efforts to support pollinators. To accomplish this, the FAST Act amended Title 23 (Highways) of the United States Code. The amendment directed the United States Secretary of Transportation, when carrying out programs under that title in conjunction with willing states, to:

  1. encourage integrated vegetation management practices on roadsides and other transportation rights-of-way, including reduced mowing; and
  2. encourage the development of habitat and forage for Monarch butterflies, other native pollinators, and honey bees through plantings of native forbs and grasses, including noninvasive, native milkweed species that can serve as migratory way stations for butterflies and facilitate migrations of other pollinators.[221]

The FAST Act also stated that activities to establish and improve pollinator habitat, forage, and migratory way stations may be eligible for Federal funding if related to transportation projects funded under Title 23.[221]

The United States Department of Agriculture's (USDA's) Farm Service Agency helps increase U.S. populations of monarch butterfly and other pollinators through its Conservation Reserve Program's State Acres for Wildlife Enhancement (SAFE) Initiative. The SAFE Initiative provides an annual rental payment to farmers who agree to remove environmentally sensitive land from agricultural production and who plant species that will improve environmental health and quality. Among other things, the initiative encourages landowners to establish wetlands, grasses, and trees to create habitats for species that the FWS has designated to be threatened or endangered.[222]

As part of its targeted monarch butterfly effort, the USDA's Natural Resources Conservation Service (NRCS) works with agricultural producers in the midwest and southern Great Plains to combat the decline of monarch butterflies by planting milkweed and other nectar-rich plants on private lands. The NRCS also provides region-specific guides and plant lists that support populations of monarch butterflies and other pollinators in the Greater Appalachian Mountains Region, the Midwest Region, the Northern and Southern Great Plains, and the Western Coastal Plain.[223]

Other actions edit

Agriculture companies and other organizations are being asked to set aside areas that remain unsprayed to allow monarchs to breed. In addition, national and local initiatives are underway to help establish and maintain pollinator habitats along corridors containing power lines and roadways. The Federal Highway Administration, state governments, and local jurisdictions are encouraging highway departments and others to limit their use of herbicides, to reduce mowing, to help milkweed to grow and to encourage monarchs to reproduce within their right-of-ways.[177][224]

National Cooperative Highway Research Program report edit

In 2020, the National Cooperative Highway Research Program (NCRHP) of the Transportation Research Board issued a 208-page report that described a project that had examined the potential for roadway corridors to provide habitat for monarch butterflies. A part of the project developed tools for roadside managers to optimize potential habitat for monarch butterflies in their road rights-of-way.[225][226]

Such efforts are controversial because the risk of butterfly mortality near roads is high. Several studies have shown that motor vehicles kill millions of monarchs and other butterflies every year.[183] Also, some evidence indicates that monarch larvae living near roads experience physiological stress conditions, as evidenced by elevations in their heart rate.[227]

The NCRHP report acknowledged that, among other hazards, roads present a danger of traffic collisions for monarchs, stating that these effects appear to be more concentrated in particular funnel areas during migration.[228] Nevertheless, the report concluded:

In summary, threats along roadway corridors exist for monarchs and other pollinators, but in the context of the amount of habitat needed for recovery of sustainable populations, roadsides are of vital importance.[228]

Butterfly gardening edit

Further information: Butterfly gardening
 
A monarch waystation near the town of Berwyn Heights in Prince George's County, Maryland (June 2017)

The practice of butterfly gardening and creating "monarch waystations" is commonly thought to increase the populations of butterflies.[229] Efforts to restore falling monarch populations by establishing butterfly gardens and monarch waystations require particular attention to the butterfly's food preferences and population cycles, as well to the conditions needed to propagate and maintain milkweed.[230]

For example, in the Washington, DC, area and elsewhere in the northeastern and midwestern United States, common milkweed (Asclepias syriaca) is among the most important food plants for monarch caterpillars.[231] A U.S. Department of Agriculture conservation planting guide for Maryland recommends that, for optimum wildlife and pollinator habitat in mesic sites (especially for monarchs), a seed mix should contain 6.0% A. syriaca by weight and 2.0% by seed.[232]

However, monarchs prefer to lay eggs on A. syriaca when its foliage is soft and fresh. Because monarch reproduction peaks in those areas during the late summer when milkweed foliage is old and tough, A. syriaca needs to be mowed or cut back in June through August to assure that it will be regrowing rapidly when monarch reproduction reaches its peak. Similar conditions exist for showy milkweed (A. speciosa) in Michigan and for green antelopehorn milkweed (A. viridis), where it grows in the Southern Great Plains and the Western United States.[83][233] Further, the seeds of A. syriaca and some other milkweeds need periods of cold treatment (cold stratification) before they will germinate.[234]

To protect seeds from washing away during heavy rains and from seed–eating birds, one can cover the seeds with a light fabric or with an 0.5-inch (13 mm) layer of straw mulch.[235] However, mulch acts as an insulator. Thicker layers of mulch can prevent seeds from germinating if they prevent soil temperatures from rising enough when winter ends. Further, few seedlings can push through a thick layer of mulch.[236]

Although monarch caterpillars will feed on butterfly weed (A. tuberosa) in butterfly gardens, it is typically not a heavily used host plant for the species.[237] The plant has rough leaves and a layer of trichomes, which may inhibit oviposition or decrease a female's ability to sense leaf chemicals.[238][239] The plant's low levels of cardenolides may also deter monarchs from laying eggs on the plant. [240] While A. tuberosa's colorful flowers provide nectar for many adult butterflies, the plant may be less suitable for use in butterfly gardens and monarch waystations than are other milkweed species.[238]

Breeding monarchs prefer to lay eggs on swamp milkweed (A. incarnata).[241] However, A. incarnata is an early successional plant that usually grows at the margins of wetlands and in seasonally flooded areas. The plant is slow to spread via seeds, does not spread by runners and tends to disappear as vegetative densities increase and habitats dry out.[242] Although A. incarnata plants can survive for up to 20 years, most live only two-five years in gardens. The species is not shade-tolerant and is not a good vegetative competitor.[242]

See also edit

References edit

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February 15, 2024
monarch, butterfly, monarch, butterfly, simply, monarch, danaus, plexippus, milkweed, butterfly, subfamily, danainae, family, nymphalidae, other, common, names, depending, region, include, milkweed, common, tiger, wanderer, black, veined, brown, amongst, most,. The monarch butterfly or simply monarch Danaus plexippus is a milkweed butterfly subfamily Danainae in the family Nymphalidae 6 Other common names depending on region include milkweed common tiger wanderer and black veined brown 7 It is amongst the most familiar of North American butterflies and an iconic pollinator 8 although it is not an especially effective pollinator of milkweeds 9 10 Its wings feature an easily recognizable black orange and white pattern with a wingspan of 8 9 10 2 cm 3 5 4 0 in 11 A Mullerian mimic the viceroy butterfly is similar in color and pattern but is markedly smaller and has an extra black stripe across each hindwing Monarch butterflyMaleFemaleConservation statusLeast Concern IUCN 3 1 1 entire species Vulnerable IUCN 3 1 2 migratory subspecies Scientific classificationDomain EukaryotaKingdom AnimaliaPhylum ArthropodaClass InsectaOrder LepidopteraFamily NymphalidaeGenus DanausSpecies D plexippusBinomial nameDanaus plexippus Linnaeus 1758 SynonymsPapilio plexippus Linnaeus 1758 Danaus archippus Fabricius 1793 3 Danaus menippe Hubner 1816 4 Anosia plexippus Moore 1883 5 D p plexippusPiedra Herrada MexicoThe eastern North American monarch population is notable for its annual southward late summer autumn instinctive migration from the northern and central United States and southern Canada to Florida and Mexico 6 During the fall migration monarchs cover thousands of miles with a corresponding multigenerational return north in spring The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern California but individuals have been found in overwintering Mexican sites as well 12 13 In 2009 monarchs were reared on the International Space Station successfully emerging from pupae located in the station s Commercial Generic Bioprocessing Apparatus 14 15 Contents 1 Etymology 2 Taxonomy 3 Genome 4 Life cycle 4 1 Egg 4 2 Larva 4 3 Pupa 4 4 Adult 5 Vision 6 Courtship and mating 7 Distribution and habitat 8 Larval host plants 9 Adult food sources 10 Flight and migration 11 Interactions with predators 11 1 Types of predators 11 2 Aposematism 11 3 Mimicry 12 Human interaction 12 1 Captive rearing 13 Threats 13 1 Western monarch populations 13 2 Eastern and midwestern monarch populations 13 2 1 Habitat loss due to herbicide use and genetically modified crops 13 2 2 Losses during migration 13 2 3 Loss of overwintering habitat 13 3 Parasites 13 4 Confusion of host plants 13 5 Climate 14 Conservation status 15 Conservation efforts 15 1 Federal actions 15 2 Other actions 15 2 1 National Cooperative Highway Research Program report 15 3 Butterfly gardening 16 See also 17 References 18 External linksEtymology editThe name monarch is believed to have been given in honor of King William III of England as the butterfly s main color is that of the king s secondary title Prince of Orange 16 The monarch was originally described by Carl Linnaeus in his Systema Naturae of 1758 and placed in the genus Papilio 17 In 1780 Jan Krzysztof Kluk used the monarch as the type species for a new genus Danaus Although works published between at least 1883 and 1944 identified the species as Anosia plexippus 18 the genus name was merged into Danaus in 2005 19 Danaus Ancient Greek Danaos a great grandson of Zeus was a mythical king in Egypt or Libya who founded Argos Plexippus Plh3ippos was one of the 50 sons of Aegyptus the twin brother of Danaus In Homeric Greek his name means one who urges on horses i e rider or charioteer 20 In the tenth edition of Systema Naturae at the bottom of page 467 21 Linnaeus wrote that the names of the Danai festivi the division of the genus to which Papilio plexippus belonged were derived from the sons of Aegyptus Linnaeus divided his large genus Papilio containing all known butterfly species into what we would now call subgenera The Danai festivi formed one of the subgenera containing colorful species as opposed to the Danai candidi containing species with bright white wings Linnaeus wrote Danaorum Candidorum nomina a filiabus Danai Aegypti Festivorum a filiis mutuatus sunt English The names of the Danai candidi have been derived from the daughters of Danaus those of the Danai festivi from the sons of Aegyptus Robert Michael Pyle suggested Danaus is a masculinized version of Danae Greek Danah Danaus s great great granddaughter to whom Zeus came as a shower of gold which seemed to him a more appropriate source for the name of this butterfly 22 Taxonomy edit nbsp White morph of the monarch in Hawaii called the white monarch source source source source source source source Monarch butterfly Ashbury Sydney 2023Monarchs belong in the subfamily Danainae of the family Nymphalidae Danainae was formerly considered a separately family Danaidae 23 The three species of monarch butterflies are D plexippus described by Linnaeus in 1758 is the species known most commonly as the monarch butterfly of North America Its range actually extends worldwide including Hawaii Australia New Zealand Spain and the Pacific Islands D erippus the southern monarch was described by Pieter Cramer in 1775 This species is found in tropical and subtropical latitudes of South America mainly in Brazil Uruguay Paraguay Argentina Bolivia Chile and southern Peru The South American monarch and the North American monarch may have been one species at one time Some researchers believe the southern monarch separated from the monarch s population some two million years ago at the end of the Pliocene Sea levels were higher and the entire Amazonas lowland was a vast expanse of brackish swamp that offered limited butterfly habitat 19 D cleophile the Jamaican monarch described by Jean Baptiste Godart in 1819 ranges from Jamaica to Hispaniola 2 Six subspecies and two color morphs of D plexippus have been identified 7 D p plexippus nominate subspecies described by Linnaeus in 1758 is the migratory subspecies known from most of North America D p p form nivosus the white monarch commonly found on Oahu Hawaii and rarely in other locations 24 D p p as yet unnamed a color morph lacking some wing vein markings 25 D p nigrippus Richard Haensch 1909 South America as forma Danais sic archippus f nigrippus Hay Roe et al in 2007 identified this taxon as a subspecies 26 D p megalippe Jacob Hubner 1826 nonmigratory subspecies and is found from Florida and Georgia southwards throughout the Caribbean and Central America to the Amazon River D p leucogyne Arthur G Butler 1884 St Thomas D p portoricensis Austin Hobart Clark 1941 Puerto Rico D p tobagi Austin Hobart Clark 1941 TobagoThe population level of the white morph in Oahu is nearing 10 On other Hawaiian islands the white morph occurs at a relatively low frequency White monarchs D p p form nivosus have been found throughout the world including Australia New Zealand Indonesia and the United States 24 However some taxonomists disagree on these classifications 19 26 Genome editThe monarch was the first butterfly to have its genome sequenced 27 12 The 273 million base pair draft sequence includes a set of 16 866 protein coding genes The genome provides researchers insights into migratory behavior the circadian clock juvenile hormone pathways and microRNAs that are differentially expressed between summer and migratory monarchs 28 29 30 More recently the genetic basis of monarch migration and warning coloration has been described 31 No genetic differentiation exists between the migratory populations of eastern and western North America 27 16 Recent research has identified the specific areas in the genome of the monarch that regulate migration No genetic difference is seen between a migrating and nonmigrating monarch but the gene is expressed in migrating monarchs but not expressed in nonmigrating monarchs 32 A 2015 publication identified genes from wasp bracoviruses in the genome of the North American monarch 33 leading to articles about monarch butterflies being genetically modified organisms 34 35 Life cycle edit nbsp The life cycle of the monarch butterflyLike all Lepidoptera monarchs undergo complete metamorphosis their life cycle has four phases egg larva pupa and adult Monarchs transition from eggs to adults during warm summer temperatures in as little as 25 days extending to as many as seven weeks during cool spring conditions During their development both larvae and their milkweed hosts are vulnerable to weather extremes predators parasites and diseases commonly fewer than 10 of monarch eggs and caterpillars survive 27 21 22 Egg edit nbsp EggThe egg is derived from materials ingested as a larva and from the spermatophores received from males during mating 36 Female monarchs lay eggs singly most often on the underside of a young leaf of a milkweed plant during the spring and summer 37 Females secrete a small amount of glue to attach their eggs directly to the plant They typically lay 300 to 500 eggs over a two to five week period 38 Eggs are cream colored or light green ovate to conical in shape and about 1 2 mm 0 9 mm 0 047 in 0 035 in in size The eggs weigh less than 0 5 mg 0 0077 gr each and have raised ridges that form longitudinally from the point to apex to the base Although each egg is 1 1000 the mass of the female she may lay up to her own mass in eggs Females lay smaller eggs as they age Larger females lay larger eggs 36 The number of eggs laid by a female which may mate several times can reach 1 180 39 Eggs take three to eight days to develop and hatch into larvae or caterpillars 27 21 The offspring s consumption of milkweed benefits health and helps defend them against predators 40 41 Monarchs lay eggs along the southern migration route 42 Larva edit nbsp Size comparison between a black swallowtail caterpillar top a monarch caterpillar middle and a queen caterpillar bottom all on a human handThe larva caterpillar has five stages instars molting at the end of each instar Instars last about 3 to 5 days depending on factors such as temperature and food availability 6 43 The first instar caterpillar that emerges from the egg is pale green or grayish white shiny and almost translucent with a large black head It lacks banding coloration or tentacles The larvae or caterpillar eats its egg case and begins to feed on milkweed with a circular motion often leaving a characteristic arc shaped hole in the leaf Older first instar larvae have dark stripes on a greenish background and develop small bumps that later become front tentacles The first instar is usually between 2 and 6 mm 0 079 and 0 236 in long 43 The second instar larva develops a characteristic pattern of white yellow and black transverse bands The larva has a yellow triangle on the head and two sets of yellow bands around this central triangle It is no longer translucent and is covered in short setae Pairs of black tentacles begin to grow a larger pair on the thorax and a smaller pair on the abdomen The second instar is usually between 6 mm 0 24 in and 1 cm 0 39 in long 43 source source source source source source source source Fifth instar monarch larva eating milkweed leaves Some at 20 speed A second instar larva grazing on leaf and cutting through a latex vein The fourth instar larva has a different banding pattern It develops white spots on the prolegs near its back and is usually between 1 5 and 2 5 cm 0 59 and 0 98 in long 43 The third instar larva has more distinct bands and the two pairs of tentacles become longer Legs on the thorax differentiate into a smaller pair near the head and larger pairs further back Third instar larvae usually feed using a cutting motion on leaf edges The third instar is usually between 1 and 1 5 cm 0 39 and 0 59 in long 43 nbsp A monarch caterpillar on milkweedThe fifth instar larva has a more complex banding pattern and white dots on the prolegs with front legs that are small and very close to the head Its length ranges from 2 5 to 4 5 cm 0 98 to 1 77 in 6 43 The larvae typically chew through a latex vein to relieve the pressure and feed above it Fifth instar larvae often chew a notch in the petiole of the leaf they are eating which relieves the latex pressure and causes the leaf to fall into a vertical position As the caterpillar completes its growth it is 4 5 cm 1 8 in long large specimens can reach 5 cm 2 0 in and 7 to 8 mm 0 28 to 0 31 in wide and weighs about 1 5 g 0 053 oz compared to the first instar which is 2 to 6 mm 0 079 to 0 236 in long and 0 5 to 1 5 mm 0 020 to 0 059 in wide Fifth instar larvae greatly increase in size and weight They then stop feeding and are often found far from milkweed plants as they seek a site for pupating 43 In a laboratory setting the fourth and fifth instar stages of the caterpillar showed signs of aggressive behavior with lower food availability Attacked caterpillars were found to be attacked when it was feeding on milkweed leaves and the caterpillars attacked when foraging for milkweed 44 This demonstrates the aggressive behavior of monarch caterpillars due to the availability of milkweed Pupa edit This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed October 2021 Learn how and when to remove this template message nbsp ChrysalisTo prepare for the pupal or chrysalis stage the caterpillar chooses a safe place for pupation where it spins a silk pad on a downward facing horizontal surface At this point it turns around and securely latches on with its last pair of hind legs and hangs upside down in the form of the letter J After J hanging for about 12 16 hours it soon straightens out its body and goes into peristalsis some seconds before its skin splits behind its head It then sheds its skin over a period of a few minutes revealing a green chrysalis At first the chrysalis is long soft and somewhat amorphous but over a few hours it compacts into its distinct shape an opaque pale green chrysalis with small golden dots near the bottom and a gold and black rim around the dorsal side near the top 45 At first its exoskeleton is soft and fragile but it hardens and becomes more durable within about a day At this point it is about 2 5 cm 0 98 in long and 10 12 mm 0 39 0 47 in wide weighing about 1 2 g 0 042 oz At normal summer temperatures it matures in 8 15 days usually 11 12 days During this pupal stage the adult butterfly forms inside A day or so before emerging the exoskeleton first becomes translucent and the chrysalis more bluish Finally within 12 hours or so it becomes transparent revealing the black and orange colors of the butterfly inside before it ecloses emerges 46 47 Adult edit This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed October 2021 Learn how and when to remove this template message nbsp An emergent monarch clinging to its chrysalis shellThe adult emerges from its chrysalis after about two weeks of pupation The emergent adult hangs upside down for several hours while it pumps fluids and air into its wings which expand dry and stiffen The butterfly then extends and retracts its wings Once conditions allow it flies and feeds on a variety of nectar plants During the breeding season adults reach sexual maturity in 4 5 days However the migrating generation does not reach maturity until overwintering is complete 48 source source source source source source source source Monarch butterflies flying and sipping nectar from milkweed flowersThe adult s wingspan ranges from 8 9 to 10 2 centimetres 3 5 to 4 0 in 11 The upper sides of the wings are tawny orange the veins and margins are black and two series of small white spots occur in the margins Monarch forewings also have a few orange spots near their tips Wing undersides are similar but the tips of forewings and hindwings are yellow brown instead of tawny orange and the white spots are larger 49 The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants 50 Wings size and shape differ between migratory and nonmigratory monarchs Monarchs from eastern North America have larger and more angular forewings than those in the western population 27 In eastern North American populations overall wing size in the physical dimensions of wings varies Males tend to have larger wings than females and are typically heavier than females Both males and females have similar thoracic dimensions Female monarchs tended to have thicker wings which is thought to convey greater tensile strength and reduce the likelihood of being damaged during migration Additionally females had lower wing loading than males which would mean females require less energy to fly 51 Adults are sexually dimorphic Males are slightly larger than females and have a black spot on a vein on each hindwing The spots contain scales that produce pheromones that many Lepidoptera use during courtship Females are often darker than males and have wider veins on their wings The ends of the abdomens of males and females differ in shape 49 52 27 53 54 55 The adult s thorax has six legs but as in all of the Nymphalidae the forelegs are small and held against the body The butterfly uses only its middle and hindlegs when walking and clinging 56 Adults typically live for 2 5 weeks during their breeding season 27 22 23 Larvae growing in high densities are smaller have lower survival and weigh less as adults compared with those growing in lower densities 57 Vision editPhysiological experiments suggest that monarch butterflies view the world through a tetrachromatic system 58 Like humans their retina contain three types of opsin proteins expressed in distinct photoreceptor cells each of which absorbs light at a different wavelength Unlike humans one of those types of photoreceptor cells corresponds to a wavelength in the ultraviolet range the other two correspond to blue and green 59 In addition to these three photoreceptors cells in the main retina monarch butterfly eyes contain orange filtering pigments that filter the light reaching some green absorbing opsins thereby making a fourth photoreceptor cell sensitive to longer wavelength light 58 The combination of filtered and unfiltered green opsins permits the butterflies to distinguish yellow from orange colors 58 The ultraviolet opsin protein has also been detected in the dorsal rim region of monarch eyes One study suggests that this allows the butterflies the ability to detect ultraviolet polarized skylight to orient themselves with the sun for their long migratory flight 60 These butterflies are capable of distinguishing colors based on their wavelength only and not based on intensity this phenomenon is termed true color vision This is important for many butterfly behaviors including seeking nectar for nourishment choosing a mate and finding milkweed on which to lay eggs One study found that floral color is more easily recognized at a distance by butterflies searching for nectar than floral shape This may be because flowers have highly contrasting colors to the green background of a vegetative landscape 61 On the other hand leaf shape is important for oviposition so that the butterflies can ensure their eggs are being laid on milkweed Beyond the perception of color the ability to remember certain colors is essential in the life of monarch butterflies These insects can easily learn to associate color and to a lesser extent shape with sugary food rewards When searching for nectar color is the first cue that draws the insect s attention toward a potential food source and shape is a secondary characteristic that promotes the process When searching for a place to lay its eggs the roles of color and shape are switched Also a difference may exist between male and female butterflies from other species in terms of the ability to learn certain colors however no differences are noted between the sexes for monarch butterflies 61 Courtship and mating edit source source source source source source source Monarch butterflies mating video Monarch courtship occurs in two phases During the aerial phase a male pursues and often forces a female to the ground During the ground phase the butterflies copulate and remain attached for about 30 to 60 minutes 62 Only 30 of mating attempts end in copulation suggesting that females may be able to avoid mating though some have more success than others 63 64 During copulation a male transfers his spermatophore to a female Along with sperm the spermatophore provides a female with nutrition which aids her in laying eggs An increase in spermatophore size increases the fecundity of female monarchs Males that produce larger spermatophores also fertilize more females eggs 65 Females and males typically mate more than once Females that mate several times lay more eggs 66 Mating for the overwintering populations occurs in the spring prior to dispersion Mating is less dependent on pheromones than in other species in its genus 67 Male search and capture strategies may influence copulatory success and human induced changes to the habitat can influence monarch mating activity at overwintering sites 68 Distribution and habitat edit nbsp String of monarchs wintering at California s Pismo State Beach Monarch Preserve 2015 The range of the western and eastern populations of D p plexippus expands and contracts depending upon the season The range differs between breeding areas migration routes and winter roosts 27 18 However no genetic differences between the western and eastern monarch populations exist 32 reproductive isolation has not led to subspeciation of these populations as it has elsewhere within the species range 27 19 In the Americas the monarch ranges from southern Canada through northern South America 6 It is also found in Bermuda the Cook Islands 69 Hawaii 70 71 Cuba 72 and other Caribbean islands 27 18 the Solomons New Caledonia New Zealand 73 Papua New Guinea 74 Australia the Azores the Canary Islands Madeira continental Portugal Gibraltar 75 the Philippines and Morocco 76 It appears in the UK in some years as an accidental migrant 77 Overwintering populations of D p plexippus are found in Mexico California along the Gulf Coast of the United States year round in Florida and in Arizona where the habitat has the specific conditions necessary for their survival 78 79 On the East Coast of the United States they have overwintered as far north as Lago Mar Virginia Beach Virginia 80 Their wintering habitat typically provides access to streams plenty of sunlight enabling body temperatures that allow flight and appropriate roosting vegetation and is relatively free of predators Overwintering roosting butterflies have been seen on basswoods elms sumacs locusts oaks osage oranges mulberries pecans willows cottonwoods and mesquites 81 While breeding monarch habitats can be found in agricultural fields pasture land prairie remnants urban and suburban residential areas gardens trees and roadsides anywhere there is access to larval host plants 82 Larval host plants editThe host plants used by the monarch caterpillar include nbsp Inflorescence of swamp milkweed one of many species of Asclepias milkweeds that serve as hosts for monarch caterpillarsAsclepias angustifolia Arizona milkweed 83 Asclepias albicans whitestem milkweed 84 Asclepias asperula antelope horns milkweed 83 Asclepias californica California milkweed 83 Asclepias cordifolia heartleaf milkweed 83 Asclepias curassavica blood flower 85 Asclepias eriocarpa woollypod milkweed 83 Asclepias erosa desert milkweed 83 Asclepias exaltata poke milkweed 83 86 Asclepias fascicularis Mexican whorled milkweed 83 Asclepias hirtella tall green milkweed 87 Asclepias humistrata sandhill pinewoods milkweed 83 Asclepias incarnata swamp milkweed 88 Asclepias lanceolata fewflower milkweed 89 Asclepias linaria pineneedle milkweed 90 Asclepias meadii Meade s milkweed 91 Asclepias nivea Caribbean milkweed 92 Asclepias oenotheroide zizotes milkweed 83 Asclepias perennis aquatic milkweed 83 Asclepias quadrifolia four leaved milkweed 93 Asclepias speciosa showy milkweed 83 94 Asclepias subulata rush milkweed 83 Asclepias sullivantii prairie milkweed 95 Asclepias syriaca common milkweed 96 Asclepias tuberosa butterfly weed 83 Asclepias variegata white milkweed 83 Asclepias verticillata whorled milkweed 83 Asclepias vestita woolly milkweed 83 Asclepias viridis green antelopehorn milkweed 83 97 Calotropis gigantea crown flower 98 Calotropis procera giant milkweed 99 Cynanchum laeve sand vine milkweed 100 Sarcostemma clausa white vine 70 101 Asclepias curassavica or tropical milkweed is often planted as an ornamental in butterfly gardens Year round plantings in the USA are controversial and criticised as they may be the cause of new overwintering sites along the U S Gulf Coast leading to year round breeding of monarchs 102 This is thought to adversely affect migration patterns and to cause a dramatic buildup of the dangerous parasite Ophryocystis elektroscirrha 103 New research also has shown that monarch larvae reared on tropical milkweed show reduced migratory development reproductive diapause and when migratory adults are exposed to tropical milkweed it stimulates reproductive tissue growth 104 Adult food sources edit nbsp Nectaring on purple coneflower Echinacea purpurea Although larvae eat only milkweed adult monarchs feed on the nectar of many plants including 105 Apocynum cannabinum Indian hemp Asclepias spp milkweed Buddleja davidii butterfly bush 106 Cirsium sp thistle Daucus carota wild carrot Dipsacus sylvestris teasel Echinacea sp coneflower Erigeron canadensis horseweed Eupatorium maculatum spotted Joe Pye weed Eupatorium perfoliatum common boneset Hesperis matronalis dame s rocket Liatris sp blazing stars Medicago sativa alfalfa Solidago sp goldenrod Symphyotrichum sp New World aster Syringa vulgaris lilac Trifolium pratense red clover Vernonia altissima tall ironweed 79 Monarchs obtain moisture and minerals from damp soil and wet gravel a behavior known as mud puddling The monarch has also been noticed puddling at an oil stain on pavement 79 Flight and migration edit nbsp Overwintering on Oyamel fir Abies religiosa Piedra Herrada MexicoFurther information Monarch butterfly migration nbsp Migrating monarchs resting on a pine tree in Fire Island National Seashore on Fire Island New York September 2021 In North America monarchs migrate both north and south on an annual basis making long distance journeys that are fraught with risks 6 This is a multi generational migration with individual monarchs only making part of the full journey 107 The population east of the Rocky Mountains attempts to migrate to the sanctuaries of the Mariposa Monarca Biosphere Reserve in the Mexican state of Michoacan and parts of Florida The western population tries to reach overwintering destinations in various coastal sites in central and southern California The overwintered population of those east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration The second third and fourth generations return to their northern locations in the United States and Canada in the spring 108 Captive raised monarchs appear capable of migrating to overwintering sites in Mexico 109 though they have a much lower migratory success rate than do wild monarchs see section on captive rearing below 110 Monarch overwintering sites have been discovered recently in Arizona 111 Monarchs from the eastern US generally migrate longer distances than monarchs from the western US 112 Since the 1800s monarchs have spread throughout the world and there are now many non migratory populations globally 113 Flight speeds of adults are around 9 km h 6 mph 114 Interactions with predators editIn both caterpillar and butterfly form monarchs are aposematic warding off predators with a bright display of contrasting colors to warn potential predators of their undesirable taste and poisonous characteristics One monarch researcher emphasizes that predation on eggs larvae or adults is natural since monarchs are part of the food chain thus people should not take steps to kill predators of monarchs 115 Larvae feed exclusively on milkweed and consume protective cardiac glycosides Toxin levels in Asclepias species vary Not all monarchs are unpalatable but exhibit Batesian or automimics Cardiac glycosides levels are higher in the abdomen and wings Some predators can differentiate between these parts and consume the most palatable ones 116 Butterfly weed A tuberosa lacks significant amounts of cardiac glycosides cardenolides but instead contains other types of toxic glycosides including pregnanes 117 118 119 This difference may reduce the toxicity of monarchs whose larvae feed on that milkweed species and affect the butterfly s breeding choices as a naturalist and others have reported that egg laying monarchs do not favor the plant 120 Some other milkweeds have similar characteristics 121 Types of predators edit While monarchs have a wide range of natural predators none of these is suspected of causing harm to the overall population or are the cause of the long term declines in winter colony sizes Several species of birds have acquired methods that allow them to ingest monarchs without experiencing the ill effects associated with the cardiac glycosides cardenolides The black backed oriole is able to eat the monarch through an exaptation of its feeding behavior that gives it the ability to identify cardenolides by taste and reject them 122 The black headed grosbeak though has developed an insensitivity to secondary plant poisons that allows it to ingest monarchs without vomiting 123 As a result these orioles and grosbeaks periodically have high levels of cardenolides in their bodies and they are forced to go on periods of reduced monarch consumption This cycle effectively reduces potential predation of monarchs by 50 and indicates that monarch aposematism has a legitimate purpose 122 The black headed grosbeak has also evolved resistance mutations in the molecular target of the heart poisons the sodium pump The specific mutations that evolved in one of the grosbeak s four copies of the sodium pump gene are the same as those found in some rodents that have also evolved to resist cardiac glycosides 124 Known bird predators include brown thrashers grackles robins cardinals sparrows scrub jays and pinyon jays 116 The monarch s white morph appeared in Oahu after the 1965 1966 introduction of two bulbul bird species Pycnonotus cafer and Pycnonotus jocosus These are now the most common avian insectivores in Hawaii and probably the only ones that eat insects as large as monarchs Although Hawaiian monarchs have low cardiac glycoside levels the birds may also be tolerant of that toxin The two species hunt the larvae and some pupae from the branches and undersides of leaves in milkweed bushes The bulbuls also eat resting and ovipositing adults but rarely flying ones Because of its color the white morph has a higher survival rate than the orange one This is either because of apostatic selection i e the birds have learned the orange monarchs can be eaten because of camouflage the white morph matches the white pubescence of milkweed or the patches of light shining through foliage or because the white morph does not fit the bird s search image of a typical monarch so is thus avoided 125 source source source source source source source source 1 A stink shield bug killing and consuming a fourth instar monarch larva 2 A mature fifth instar larva jerking to dislodge a large milkweed bug a herbivore 3 A fourth instar larva killed by insect parasitoids non insect parasites or a pathogen Some mice particularly the black eared mouse Peromyscus melanotis are like all rodents able to tolerate large doses of cardenolides and are able to eat monarchs 126 Overwintering adults become less toxic over time making them more vulnerable to predators In Mexico about 14 of the overwintering monarchs are eaten by birds and mice and black eared mice can eat up to 40 monarchs per night 78 126 In North America eggs and first instar larvae of the monarch are eaten by larvae and adults of the introduced Asian lady beetle Harmonia axyridis 127 The Chinese mantis Tenodera sinensis will consume the larvae once the gut is removed thus avoiding cardenolides 128 Predatory wasps commonly consume larvae 129 Many Hemipteran bugs including predatory stink bugs in the subfamily Asopinae and assassin bugs in family Reduviidae eat monarchs Larvae can sometimes avoid predation by dropping from the plant or by jerking their bodies 130 Parasitoids including tachinid flies and braconid wasps develop inside the monarch larvae eventually killing it and emerging from the larvae or pupa Non insect parasites and infectious diseases pathogens also kill monarchs Aposematism edit nbsp Chemical structure of oleandrin one of the cardiac glycosidesMonarchs are toxic and foul tasting because of the presence of cardenolides in their bodies which the caterpillars ingest as they feed on milkweed 67 Monarchs and other cardenolide resistant insects rely on a resistant form of the Na K ATPase enzyme to tolerate significantly higher concentrations of cardenolides than nonresistant species 131 By ingesting a large amount of plants in the genus Asclepias primarily milkweed monarch caterpillars are able to sequester cardiac glycosides or more specifically cardenolides which are steroids that act in heart arresting ways similar to digitalis 132 It has been found that monarchs are able to sequester cardenolides most effectively from plants of intermediate cardenolide content rather than those of high or low content 133 Three mutations that evolved in the monarch s Na K ATPase were found to be sufficient together to confer resistance to dietary cardiac glycosides 131 This was tested by swapping these mutations into the same gene in the fruit fly Drosophila melanogaster using CRISPR Cas9 genome editing These fruit flies turned monarch flies 134 were completely resistant to dietary ouabain a cardiac glycoside found in Apocynaceae and even sequestered some through metamorphosis like the monarch 131 Different species of milkweed have different effects on growth virulence and transmission of parasites 135 One species Asclepias curassavica appears to reduce the symptoms of Ophryocystis elektroscirrha OE infection The two possible explanations for this include that it promotes overall monarch health to boost the monarch s immune system or that chemicals from the plant have a direct negative effect on the OE parasites 135 A curassavica does not cure or prevent the infection with OE it merely allows infected monarchs to live longer and this would allow infected monarchs to spread the OE spores for longer periods For the average home butterfly garden this scenario only adds more OE to the local population 136 After the caterpillar becomes a butterfly the toxins shift to different parts of the body Since many birds attack the wings of the butterfly having three times the cardiac glycosides in the wings leaves predators with a very foul taste and may prevent them from ever ingesting the body of the butterfly 132 To combat predators that remove the wings only to ingest the abdomen monarchs keep the most potent cardiac glycosides in their abdomens 137 Mimicry edit nbsp Monarch left and viceroy right butterflies exhibiting Mullerian mimicryMonarchs share the defense of noxious taste with the similar appearing viceroy butterfly in what is perhaps one of the most well known examples of mimicry Though long purported to be an example of Batesian mimicry the viceroy is actually more unpalatable than the monarch making this a case of Mullerian mimicry 138 Human interaction editThe monarch is the state insect of Alabama 139 Idaho 140 Illinois 141 Minnesota 142 Texas 143 Vermont 144 and West Virginia 145 Legislation was introduced to make it the national insect of the United States 146 but this failed in 1989 147 and again in 1991 148 Homeowners are increasingly establishing butterfly gardens monarchs can be attracted by cultivating a butterfly garden with specific milkweed species and nectar plants Efforts are underway to establish these monarch waystations 149 An IMAX film Flight of the Butterflies describes the story of the Urquharts Brugger and Trail to document the then unknown monarch migration to Mexican overwintering areas 150 Sanctuaries and reserves have been created at overwintering locations in Mexico and California to limit habitat destruction These sites can generate significant tourism revenue 151 However with less tourism monarch butterflies will have a higher survival rate because they show more protein content and a higher value of immune response and oxidative defense 152 Organizations and individuals participate in tagging programs Tagging information is used to study migration patterns 153 The 2012 novel by Barbara Kingsolver Flight Behavior deals with the fictional appearance of a large population in the Appalachians 154 Captive rearing edit Humans interact with monarchs when rearing them in captivity which has become increasingly popular However risks occur in this controversial activity On one hand captive rearing has many positive aspects Monarchs are bred in schools and used for butterfly releases at hospices memorial events and weddings 155 Memorial services for the September 11 attacks include the release of captive bred monarchs 156 157 158 Monarchs are used in schools and nature centers for educational purposes 159 Many homeowners raise monarchs in captivity as a hobby and for educational purposes 160 On the other hand this practice becomes problematic when monarchs are mass reared Stories in the Huffington Post in 2015 and Discover magazine in 2016 have summarized the controversy around this issue 161 162 The frequent media reports of monarch declines have encouraged many homeowners to attempt to rear as many monarchs as possible in their homes and then release them to the wild in an effort to boost the monarch population Some individuals such as one in Linn County Iowa have reared thousands of monarchs at the same time 163 Some monarch scientists do not condone the practice of rearing large numbers of monarchs in captivity for release into the wild because of the risks of genetic issues and disease spread 164 One of the biggest concerns of mass rearing is the potential for spreading the monarch parasite Ophryocystis elektroscirrha into the wild This parasite can rapidly build up in captive monarchs especially if they are housed together The spores of the parasite also can quickly contaminate all housing equipment so that all subsequent monarchs reared in the same containers then become infected One researcher stated that rearing more than 100 monarchs constitutes mass rearing and should not be done 165 In addition to the disease risks researchers believe these captive reared monarchs are not as fit as wild ones owing to the unnatural conditions in which they are raised Homeowners often raise monarchs in plastic or glass containers in their kitchens basements porches etc and under artificial lighting and controlled temperatures Such conditions would not mimic what the monarchs are used to in the wild and may result in adults that are unsuited for the realities of their wild existence In support of this a recent study by a citizen scientist found that captive reared monarchs have a lower migration success rate than wild monarchs do 110 A 2019 study shed light on the fitness of captive reared monarchs by testing reared and wild monarchs on a tethered flight apparatus that assessed navigational ability 166 In that study monarchs that were reared to adulthood in artificial conditions showed a reduction in navigational ability This happened even with monarchs that were brought into captivity from the wild for a few days A few captive reared monarchs did show proper navigation This study revealed the fragility of monarch development if the conditions are not suitable their ability to properly migrate could be impaired The same study also examined the genetics of a collection of reared monarchs purchased from a butterfly breeder and found they were dramatically different from wild monarchs so much so that the lead author described them as franken monarchs 167 An unpublished study in 2019 compared behavior of captive reared versus wild monarch larvae 168 The study showed that reared larvae exhibited more defensive behavior than wild larvae The reason for this is unknown but it could relate to the fact that reared larvae are frequently handled and or disturbed Threats editIn February 2015 the U S Fish and Wildlife Service reported a study that showed that nearly a billion monarchs had vanished from the butterfly s overwintering sites since 1990 The agency attributed the monarch s decline in part to a loss of milkweed caused by herbicides that farmers and homeowners had used 169 Western monarch populations edit See also Threats to monarch butterfly in California nbsp Western monarch populations from 1997 to 2013 from Xerces Society data Based on a 2014 20 year comparison the overwintering numbers west of the Rocky Mountains have dropped more than 50 since 1997 and the overwintering numbers east of the Rockies have declined by more than 90 since 1995 According to the Xerces Society the monarch population in California decreased 86 in 2018 going from millions of butterflies to tens of thousands of butterflies 170 The society s annual 2020 2021 winter count showed a significant decline in the California population One Pacific Grove site did not have a single monarch butterfly A primary explanation for this was the destruction of the butterfly s milkweed habitats 27 171 This particular population is believed to comprise less than 2000 individuals as of 2022 update 172 Eastern and midwestern monarch populations edit nbsp Area covered by monarchs D plexippus eastern migratory population in their overwintering areas in Mexico between 1993 and 2018A 2016 publication attributed the previous decade s 90 decline in overwintering numbers of the eastern monarch population to the loss of breeding habitat and milkweed The publication s authors stated that an 11 57 probability existed that this population will go almost extinct over the next 20 years 173 Chip Taylor the director of Monarch Watch at the University of Kansas has stated that the Midwest milkweed habitat is virtually gone with 120 150 million acres lost 174 175 To help fight this problem Monarch Watch encourages the planting of Monarch Waystations 160 Habitat loss due to herbicide use and genetically modified crops edit Declines in milkweed abundance and monarch populations between 1999 and 2010 are correlated with the adoption of herbicide tolerant genetically modified GM corn and soybeans which now constitute 89 and 94 of these crops respectively in the U S 173 GM corn and soybeans are resistant to the effect of the herbicide glyphosate Some conservationists attribute the disappearance of milkweed to agricultural practices in the Midwest where GM seeds are bred to resist herbicides that farmers use to kill unwanted plants that grow near their rows of food crops 176 177 In 2015 the Natural Resources Defense Council filed a suit against the United States Environmental Protection Agency EPA The Council argued that the agency ignored warnings about the dangers of glyphosate usage for monarchs 178 However a 2018 study has suggested that the decline in milkweed predates the arrival of GM crops 179 Losses during migration edit nbsp Monarch nectaring on a zinnia flower during its migration southward to Mexico late September of 2022Eastern and midwestern monarchs are apparently experiencing problems reaching Mexico A number of monarch researchers have cited recent evidence obtained from long term citizen science data that show that the number of breeding adult monarchs has not declined in the last two decades 180 181 182 The lack of long term declines in the numbers of breeding and migratory monarchs yet the clear declines in overwintering numbers suggests a growing disconnect exists between these life stages One researcher has suggested that mortality from car strikes constitutes an increasing threat to migrating monarchs 183 A study of road mortality in northern Mexico published in 2019 showed very high mortality from just two hotspots each year amounting to 200 000 monarchs killed 184 Loss of overwintering habitat edit This section needs to be updated Please help update this article to reflect recent events or newly available information August 2021 The area of Mexican forest to which eastern and midwestern monarchs migrate reached its lowest level in two decades in 2013 The decline was expected to increase during the 2013 2014 season Mexican environmental authorities continue to monitor illegal logging of the oyamel trees The oyamel is a major species of evergreen on which the overwintering butterflies spend a significant time during their winter diapause or suspended development 185 A 2014 study acknowledged that while the protection of overwintering habitat has no doubt gone a long way towards conserving monarchs that breed throughout eastern North America their research indicates that habitat loss on breeding grounds in the United States is the main cause of both recent and projected population declines 186 Western monarch populations have rebounded slightly since 2014 with the Western Monarch Thanksgiving Count 187 tallying 335 479 monarchs in 2022 The population still has much to go for a full recovery Parasites edit nbsp Pteromalus cassotis on monarch chrysalisParasites include the tachinid flies Sturmia convergens 188 and Lespesia archippivora Lesperia parasitized butterfly larvae suspend but die prior to pupation The fly s maggot lowers itself to the ground forms a brown puparium and then emerges as an adult 189 Pteromalid wasps specifically Pteromalus cassotis parasitize monarch pupae 190 These wasps lay their eggs in the pupae while the chrysalis is still soft Up to 400 adults emerge from the chrysalis after 14 20 days 190 killing the monarch The bacterium Micrococcus flacidifex danai also infects larvae Just before pupation the larvae migrate to a horizontal surface and die a few hours later attached only by one pair of prolegs with the thorax and abdomen hanging limp The body turns black shortly thereafter The bacterium Pseudomonas aeruginosa has no invasive powers but causes secondary infections in weakened insects It is a common cause of death in laboratory reared insects 189 Ophryocystis elektroscirrha is another parasite of the monarch It infects the subcutaneous tissues and propagates by spores formed during the pupal stage The spores are found over all of the body of infected butterflies with the greatest number on the abdomen These spores are passed from female to caterpillar when spores rub off during egg laying and are then ingested by caterpillars Severely infected individuals are weak unable to expand their wings or unable to eclose and have shortened lifespans but parasite levels vary in populations This is not the case in laboratory rearing where after a few generations all individuals can be infected 191 Infection with O elektroscirrha creates an effect known as culling whereby migrating monarchs that are infected are less likely to complete the migration This results in overwintering populations with lower parasite loads 192 Owners of commercial butterfly breeding operations claim that they take steps to control this parasite in their practices 193 although this claim is doubted by many scientists who study monarchs 194 Confusion of host plants edit The black swallow wort Cynanchum louiseae and pale swallow wort Cynanchum rossicum plants are problematic for monarchs in North America Monarchs lay their eggs on these relatives of native vining milkweed Cynanchum laeve because they produce stimuli similar to milkweed Once the eggs hatch the caterpillars are poisoned by the toxicity of this invasive plant from Europe 195 Climate edit Climate variations during the fall and summer affect butterfly reproduction Rainfall and freezing temperatures affect milkweed growth Omar Vidal director general of WWF Mexico said The monarch s lifecycle depends on the climatic conditions in the places where they breed Eggs larvae and pupae develop more quickly in milder conditions Temperatures above 35 C 95 F can be lethal for larvae and eggs dry out in hot arid conditions causing a drastic decrease in hatch rate 196 If a monarch s body temperatures is below 30 C 86 F a monarch cannot fly To warm up they sit in the sun or rapidly shiver their wings to warm themselves 197 Climate change may dramatically affect the monarch migration A study from 2015 examined the impact of warming temperatures on the breeding range of the monarch and showed that in the next 50 years the monarch host plant will expand its range further north into Canada and that the monarchs will follow this 198 While this will expand the breeding locations of the monarch it will also have the effect of increasing the distance that monarchs must travel to reach their overwintering destination in Mexico which could result in greater mortality during the migration 199 Milkweeds grown at increased temperatures have been shown to contain higher cardenolide concentrations making the leaves too toxic for the monarch caterpillars However these increased concentrations are likely in response to increased insect herbivory which is also caused by the increased temperatures Whether increased temperatures make milkweed too toxic for monarch caterpillars when other factors are not present is unknown 200 Additionally milkweed grown at carbon dioxide levels of 760 parts per million was found to produce a different mix of the toxic cardenolides one of which was less effective against monarch parasites 201 Conservation status editOn July 20 2022 the International Union for Conservation of Nature added the migratory monarch butterfly the subspecies common in North America to its red list of endangered species 202 2 The monarch butterfly is not currently listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora or protected specifically under U S domestic laws 203 On August 14 2014 the Center for Biological Diversity and the Center for Food Safety filed a legal petition requesting Endangered Species Act protection for the monarch and its habitat 27 based largely on the long term trends observed at overwintering sites The U S Fish and Wildlife Service FWS initiated a status review of the monarch butterfly under the Endangered Species Act with a due date for information submission of March 3 2015 later extended to 2020 On December 15 2020 the FWS ruled that adding the butterfly to the list of threatened and endangered species was warranted but precluded because it needed to devote its resources to 161 higher priority species 204 The number of monarchs overwintering in Mexico has shown a long term downward trend Since 1995 coverage numbers have been as high as 18 hectares 44 acres during the winter of 1996 1997 but on average about 6 hectares 15 acres Coverage declined to its lowest point to date 0 67 hectares 1 66 acres during the winter of 2013 2014 but rebounded to 4 01 hectares 10 acres in 2015 2016 The average population of monarchs in 2016 was estimated at 200 million Historically on average there are 300 million monarchs The 2016 increase was attributed to favorable breeding conditions in the summer of 2015 However coverage declined by 27 to 2 91 hectares 7 19 acres during the winter of 2016 2017 Some believe this was because of a storm that had occurred during March 2016 in the monarchs previous overwintering season 205 206 207 though this seems unlikely since most current research shows that the overwintering colony sizes do not predict the size of the next summer breeding population 208 In Ontario Canada the monarch butterfly is listed as a species of special concern 209 In fall 2016 the Committee on the Status of Endangered Wildlife in Canada proposed that the monarch be listed as endangered in Canada as opposed to its current listing as a species of concern in that country This move once enacted would protect critical monarch habitat in Canada such as major fall accumulation areas in southern Ontario but it would also have implications for citizen scientists who work with monarchs and for classroom activities If the monarch were federally protected in Canada these activities could be limited or require federal permits 210 In Nova Scotia the monarch is listed as endangered at the provincial level as of 2017 update This decision as well as the Ontario decision apparently is based on a presumption that the overwintering colony declines in Mexico create declines in the breeding range in Canada 211 Two recent studies have been conducted examining long term trends in monarch abundance in Canada using either butterfly atlas records 212 or citizen science butterfly surveys 213 and neither shows evidence of a population decline in Canada Conservation efforts editSee also Monarch butterfly conservation in California Although numbers of breeding monarchs in eastern North America have apparently not decreased reports of declining numbers of overwintering butterflies have inspired efforts to conserve the species 180 181 182 Federal actions edit On June 20 2014 President Barack Obama issued a presidential memorandum entitled Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators The memorandum established a Pollinator Health Task Force to be co chaired by the Secretary of Agriculture and the Administrator of the Environmental Protection Agency and stated The number of migrating Monarch butterflies sank to the lowest recorded population level in 2013 14 and there is an imminent risk of failed migration 214 In May 2015 the Pollinator Health Task Force issued a National Strategy to Promote the Health of Honey Bees and Other Pollinators The strategy laid out federal actions to achieve three goals two of which were Monarch Butterflies Increase the Eastern population of the monarch butterfly to 225 million butterflies occupying an area of approximately 15 acres 6 hectares in the overwintering grounds in Mexico through domestic international actions and public private partnerships by 2020 Pollinator Habitat Acreage Restore or enhance 7 million acres of land for pollinators over the next 5 years through Federal actions and public private partnerships 215 216 Many of the priority projects that the national strategy identified focused on the I 35 corridor which extends for 1 500 miles 2 400 km from Texas to Minnesota The area through which that highway travels provides spring and summer breeding habitats in the United States key monarch migration corridor 215 216 The Task Force simultaneously issued a Pollinator Research Action Plan The Plan outlined five main action areas covered in ten subject specific chapters The action areas were 1 Setting a Baseline 2 Assessing Environmental Stressors 3 Restoring Habitat 4 Understanding and Supporting Stakeholders 5 Curating and Sharing Knowledge 216 217 In June 2016 the Task Force issued a Pollinator Partnership Action Plan That Plan provided examples of past ongoing and possible future collaborations between the federal government and non federal institutions to support pollinator health under each of the national strategy s goals 218 The U S General Services Administration GSA publishes sets of landscape performance requirements in its P100 documents which mandate standards for the GSA s Public Buildings Service Beginning in March 2015 those performance requirements and their updates have included four primary aspects for planting designs that are intended to provide adequate on site foraging opportunities for targeted pollinators The targeted pollinators include bees butterflies and other beneficial insects 219 On December 4 2015 President Obama signed into law the Fixing America s Surface Transportation FAST Act Pub L 114 94 220 The FAST Act placed a new emphasis on efforts to support pollinators To accomplish this the FAST Act amended Title 23 Highways of the United States Code The amendment directed the United States Secretary of Transportation when carrying out programs under that title in conjunction with willing states to encourage integrated vegetation management practices on roadsides and other transportation rights of way including reduced mowing and encourage the development of habitat and forage for Monarch butterflies other native pollinators and honey bees through plantings of native forbs and grasses including noninvasive native milkweed species that can serve as migratory way stations for butterflies and facilitate migrations of other pollinators 221 The FAST Act also stated that activities to establish and improve pollinator habitat forage and migratory way stations may be eligible for Federal funding if related to transportation projects funded under Title 23 221 The United States Department of Agriculture s USDA s Farm Service Agency helps increase U S populations of monarch butterfly and other pollinators through its Conservation Reserve Program s State Acres for Wildlife Enhancement SAFE Initiative The SAFE Initiative provides an annual rental payment to farmers who agree to remove environmentally sensitive land from agricultural production and who plant species that will improve environmental health and quality Among other things the initiative encourages landowners to establish wetlands grasses and trees to create habitats for species that the FWS has designated to be threatened or endangered 222 As part of its targeted monarch butterfly effort the USDA s Natural Resources Conservation Service NRCS works with agricultural producers in the midwest and southern Great Plains to combat the decline of monarch butterflies by planting milkweed and other nectar rich plants on private lands The NRCS also provides region specific guides and plant lists that support populations of monarch butterflies and other pollinators in the Greater Appalachian Mountains Region the Midwest Region the Northern and Southern Great Plains and the Western Coastal Plain 223 Other actions edit Agriculture companies and other organizations are being asked to set aside areas that remain unsprayed to allow monarchs to breed In addition national and local initiatives are underway to help establish and maintain pollinator habitats along corridors containing power lines and roadways The Federal Highway Administration state governments and local jurisdictions are encouraging highway departments and others to limit their use of herbicides to reduce mowing to help milkweed to grow and to encourage monarchs to reproduce within their right of ways 177 224 National Cooperative Highway Research Program report edit In 2020 the National Cooperative Highway Research Program NCRHP of the Transportation Research Board issued a 208 page report that described a project that had examined the potential for roadway corridors to provide habitat for monarch butterflies A part of the project developed tools for roadside managers to optimize potential habitat for monarch butterflies in their road rights of way 225 226 Such efforts are controversial because the risk of butterfly mortality near roads is high Several studies have shown that motor vehicles kill millions of monarchs and other butterflies every year 183 Also some evidence indicates that monarch larvae living near roads experience physiological stress conditions as evidenced by elevations in their heart rate 227 The NCRHP report acknowledged that among other hazards roads present a danger of traffic collisions for monarchs stating that these effects appear to be more concentrated in particular funnel areas during migration 228 Nevertheless the report concluded In summary threats along roadway corridors exist for monarchs and other pollinators but in the context of the amount of habitat needed for recovery of sustainable populations roadsides are of vital importance 228 Butterfly gardening edit Further information Butterfly gardening nbsp A monarch waystation near the town of Berwyn Heights in Prince George s County Maryland June 2017 The practice of butterfly gardening and creating monarch waystations is commonly thought to increase the populations of butterflies 229 Efforts to restore falling monarch populations by establishing butterfly gardens and monarch waystations require particular attention to the butterfly s food preferences and population cycles as well to the conditions needed to propagate and maintain milkweed 230 For example in the Washington DC area and elsewhere in the northeastern and midwestern United States common milkweed Asclepias syriaca is among the most important food plants for monarch caterpillars 231 A U S Department of Agriculture conservation planting guide for Maryland recommends that for optimum wildlife and pollinator habitat in mesic sites especially for monarchs a seed mix should contain 6 0 A syriaca by weight and 2 0 by seed 232 However monarchs prefer to lay eggs on A syriaca when its foliage is soft and fresh Because monarch reproduction peaks in those areas during the late summer when milkweed foliage is old and tough A syriaca needs to be mowed or cut back in June through August to assure that it will be regrowing rapidly when monarch reproduction reaches its peak Similar conditions exist for showy milkweed A speciosa in Michigan and for green antelopehorn milkweed A viridis where it grows in the Southern Great Plains and the Western United States 83 233 Further the seeds of A syriaca and some other milkweeds need periods of cold treatment cold stratification before they will germinate 234 To protect seeds from washing away during heavy rains and from seed eating birds one can cover the seeds with a light fabric or with an 0 5 inch 13 mm layer of straw mulch 235 However mulch acts as an insulator Thicker layers of mulch can prevent seeds from germinating if they prevent soil temperatures from rising enough when winter ends Further few seedlings can push through a thick layer of mulch 236 Although monarch caterpillars will feed on butterfly weed A tuberosa in butterfly gardens it is typically not a heavily used host plant for the species 237 The plant has rough leaves and a layer of trichomes which may inhibit oviposition or decrease a female s ability to sense leaf chemicals 238 239 The plant s low levels of cardenolides may also deter monarchs from laying eggs on the plant 240 While A tuberosa s colorful flowers provide nectar for many adult butterflies the plant may be less suitable for use in butterfly gardens and monarch waystations than are other milkweed species 238 Breeding monarchs prefer to lay eggs on swamp milkweed A incarnata 241 However A incarnata is an early successional plant that usually grows at the margins of wetlands and in seasonally flooded areas The plant is slow to spread via seeds does not spread by runners and tends to disappear as vegetative densities increase and habitats dry out 242 Although A incarnata plants can survive for up to 20 years most live only two five years in gardens The species is not shade tolerant and is not a good vegetative competitor 242 See also editButterfly house Lepidoptera migration Peninsula Point Light MichiganReferences edit Walker A Thogmartin W E Oberhauser K S Pelton E M Pleasants J M 2022 Danaus plexippus IUCN Red List of 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Akdavis6 wixsite com December 31 2016 Retrieved January 6 2017 monarchscience Akdavis6 wixsite com April 5 2016 a b Barbosa Pedro Deborah Kay Letourneau 1988 5 Novel Aspects of Insect plant Interactions Wiley Interscience pp 29 31 ISBN 978 0 471 83276 8 Butterfly Weed Asclepias tuberosa PDF Becker County Minnesota Becker Soil and Water Conservation District Archived PDF from the original on September 11 2020 Retrieved September 11 2020 Unlike other milkweeds this plant has a clear sap and the level of toxic cardiac glycosides is consistently low although other toxic compounds may be present Mikkelsen Lauge Hjorth Hamoudi Hassan Altuntas Gul Cigdem Heegaard Steffen 2017 Corneal Toxicity Following Exposure to Asclepias tuberosa The Open Ophthalmology Journal Bentham Science Publishers 11 1 4 doi 10 2174 1874364101711010001 PMC 5362972 PMID 28400886 The latex of A tuberosa seems to be different from other Asclepias species due to the fact that even though cardenolides are normally present in Asclepias species these cardenolides have not been found in A tuberosa Instead some unique pregnane glycosides are found in A tuberosa Warashina Tsutomu Noro Tadataka February 2010 8 12 8 20 Diepoxy 8 14 secopregnane Glycosides from the Aerial Parts of Asclepias tuberosa Chemical and Pharmaceutical Bulletin Pharmaceutical Society of Japan 58 2 172 179 doi 10 1248 cpb 58 172 PMID 20118575 Retrieved September 11 2020 Though cardenolides are considered to be characteristic constituents of Asclepias spp together with pregnane glycosides we could find no cardenolides in the more hydrophobic fraction of the methanol extract of the aerial parts of A tuberosa the same as previously Multiple sources Gunn John May 20 2016 Milkweeds mostly Asclepias spp Alonso Abugattas Shares Native Plant Picks for Wildlife Mid Atlantic Gardener John Gunn Archived from the original on October 21 2020 Retrieved October 17 2020 And if you have hot dry conditions in your yard try Butterflyweed A tuberosa It s the least favored by Monarch caterpillars because it has very little toxin cardiac glycosides in its leaves Abugattas Alonzo January 3 2017 Monarch Way Stations Capital Naturalist Archived from the original on June 5 2017 Retrieved June 5 2017 via Blogger A tuberosa is the least favored by monarch caterpillars because it has very little toxin cardiac glycosides in its leaves Gomez Tony Asclepias tuberosa Butterfly Weed for Monarchs and More Monarch Butterfly Garden MonarchButterflyGarden net Archived from the original on August 16 2017 Retrieved October 17 2010 Rough leaves for monarch caterpillars not typically a heavily used host plant Butterfly Society of Virginia 2019 Growing Milkweed Archived from the original on June 24 2019 Retrieved December 25 2023 I ve grown butterfly weed swamp milkweed Asclepias currassavica bloodflower Asclepias syriaca common milkweed and Asclepias verticillata whorled milkweed I ve found that butterfly weed is the least favorite of my Monarch guests in my Virginia Beach garden for laying eggs perhaps the leaves are tougher Pocius Victoria M Debinski Diane M Pleasants John M Bidne Keith G Hellmich Richard L January 8 2018 Monarch butterflies do not place all of their eggs in one basket oviposition on nine Midwestern milkweed species Ecosphere Ecological Society of America 9 1 1 13 doi 10 1002 ecs2 2064 Archived from the original on December 25 2023 Retrieved January 7 2024 In our study the least preferred milkweed species A tuberosa no choice Fig 2 and A verticillata choice Fig 3A both have low cardenolide levels recorded in the literature Roeske et al 1976 Agrawal et al 2009 2015 Rasmann and Agrawal 2011 Pocius Victoria M Debinski Diane M Pleasants John M Bidne Keith G Hellmich Richard L January 8 2018 Monarch butterflies do not place all of their eggs in one basket oviposition on nine Midwestern milkweed species Ecosphere Ecological Society of America 9 1 1 13 doi 10 1002 ecs2 2064 Archived from the original on December 25 2023 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resistance toxic food plants can select for virulent parasites of monarch butterflies Journal of Evolutionary Biology 24 4 712 722 doi 10 1111 j 1420 9101 2010 02213 x PMID 21261772 S2CID 1533504 Is tropical milkweed really medicinal answer yes and that s really really bad for your garden monarchscience March 16 2017 Retrieved December 12 2019 Glazier Lincoln Susan Glazier 1975 Localization of Heart Poisons in the Monarch Butterfly Science 188 4183 19 25 Bibcode 1975Sci 188 19B doi 10 1126 science 188 4183 19 PMID 17760150 S2CID 44509809 Ritland D L P Brower 1991 The viceroy butterfly is not a Batesian mimic Nature 350 6318 497 498 Bibcode 1991Natur 350 497R doi 10 1038 350497a0 S2CID 28667520 Viceroys are as unpalatable as monarchs and significantly more unpalatable than queens from representative Florida populations Official Alabama Insect Alabama Emblems Symbols and Honors Alabama Department of Archives amp History July 12 2001 Archived from the original on October 14 2018 Retrieved March 19 2007 Idaho Symbols Insect Monarch Butterfly Idaho State Symbols Emblems and Mascots SHG resources state handbook amp guide Archived from the original on February 8 2012 Retrieved March 26 2008 State Symbol Illinois Official Insect Monarch Butterfly Danaus plexippus Illinois State Symbols Illinois State Museum Retrieved March 26 2008 Minnesota State Symbols PDF Minnesota House of Representatives Retrieved March 26 2008 Texas State Symbols The Texas State Library and Archives Archived from the original on December 24 2018 Retrieved March 26 2008 Vermont State Butterfly Vermont Department of Libraries Archived from the original on May 18 2008 Retrieved March 26 2008 West Virginia Statistical Information General State Information PDF Official West Virginia Web Portal Archived from the original PDF on April 11 2008 Retrieved March 26 2008 Wade Nicholas June 1 1990 Choosing a National Bug The New York Times Retrieved September 27 2017 Designating the monarch butterfly as the 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Archived from the original on April 14 2020 Retrieved January 12 2017 Love Orlan August 25 2016 Monarch Moonshot Officials hope to make Linn County center of butterfly production and habitat The Gazette Retrieved January 12 2017 Rearing Monarchs Responsibly A conservationist s guide to raising monarchs for science and education Archived September 14 2021 at the Wayback Machine Monarch Joint Venture University of Minnesota monarchscience Akdavis6 wixsite com September 7 2015 Tenger Trolander Ayse Lu Wei Noyes Michelle Kronforst Marcus R July 16 2019 Contemporary loss of migration in monarch butterflies Proceedings of the National Academy of Sciences of the United States of America 116 29 14671 14676 Bibcode 2019PNAS 11614671T doi 10 1073 pnas 1904690116 ISSN 0027 8424 PMC 6642386 PMID 31235586 Maeckle Monika July 2 2019 Study of genetic franken monarchs provokes online ire and debate texasbutterflyranch Retrieved December 12 2019 Effects of captive rearing on caterpillar anti predator behavior an inside look at some preliminary data monarchscience August 10 2019 Retrieved December 12 2019 Fears Darryl August 26 2015 As pesticides wipe out Monarch butterflies in the U S illegal logging is doing the same in Mexico The Washington Post The Monarch butterfly population in California has plummeted 86 in one year January 7 2019 Monarch butterfly population moves closer to extinction phys org Retrieved January 21 2021 Dellinger AJ July 21 2022 The monarch butterfly is endangered now you monsters Mic Retrieved July 22 2022 a b Semmens Brice X Semmens Darius J Thogmartin Wayne E Wiederholt Ruscena Lopez Hoffman Laura Diffendorfer Jay E Pleasants John M Oberhauser Karen S Taylor Orley R 2016 Quasi extinction risk and population targets for the Eastern migratory population of monarch butterflies Danaus plexippus Scientific Reports 6 23265 Bibcode 2016NatSR 623265S doi 10 1038 srep23265 PMC 4800428 PMID 26997124 Conniff Richard April 1 2013 Tracking the Causes of Sharp Decline of the Monarch Butterfly Yale University Wines Michael March 13 2013 Monarch Migration Plunges to Lowest Level in Decades The New York Times Pleasants John M Oberhauser Karen S 2012 Milkweed loss in agricultural fields because of herbicide use effect on the monarch butterfly population PDF Insect Conservation and Diversity 6 2 135 144 doi 10 1111 j 1752 4598 2012 00196 x S2CID 14595378 Archived from the original PDF on September 4 2014 a b Brennen Shannon July 2014 For Love of Nature Annual monarch butterfly migration in peril The News amp Advance Lynchburg Virginia Retrieved July 4 2014 NRDC Sues EPA Over Demise of Monarch Butterfly Population NBC 2015 Puzey J R Dalgleish H J Boyle J H February 5 2019 Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops Proceedings of the National Academy of Sciences of the United States of America 116 8 3006 3011 Bibcode 2019PNAS 116 3006B doi 10 1073 pnas 1811437116 ISSN 0027 8424 PMC 6386695 PMID 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Migration in Northeast Mexico Frontiers in Ecology and Evolution 7 doi 10 3389 fevo 2019 00273 ISSN 2296 701X Paz Fatima June 18 2014 En espera de aprobacion de la Profepa por tala ilegal en la Reserva de la Mariposa Monarca Archived September 3 2014 at the Wayback Machine cambiodemichoacan com mx Habitat Loss on Breeding Grounds Cause of Monarch Decline U of G Study Finds University of Guelph June 4 2014 Retrieved March 17 2015 Western Monarch Population Rebound Continues in 2022 but Winter Storms Could Impact Spring Breeding Population Farmers for Monarchs February 1 2023 Retrieved April 14 2023 Clarke A R Zalucki M P 2001 Taeniogonalos raymenti Carmean amp Kimsey Hymenoptera Trigonalidae reared as a hyperparasite of Sturmia convergens Weidemann Diptera Tachinidae a primary parasite of Danaus plexippus L Lepidoptera Nymphalidae Pan Pacific Entomologist 77 68 70 a b Brewer Jo Gerard M Thomas 1966 Causes of death encountered during rearing of Danaus plexippus Danaidae PDF Journal of 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determination means that every year it will consider adding the butterfly to the list until it decides to propose listing it or determines that protections are not warranted Howard Elizabeth February 26 2016 Monarch Population Size Announced Journey North Archived from the original on February 28 2016 Retrieved June 6 2017 Eastern Monarch Population Numbers Drop 27 News The Monarch Joint Venture February 16 2017 Archived from the original on June 5 2017 Retrieved June 5 2017 Where Are All The Monarchs Monarch Lab University of Minnesota Extension July 14 2016 Archived from the original on August 22 2016 Retrieved June 5 2017 Another monarch study published showing the spring migration holds the key to everything monarchscience November 4 2019 Retrieved December 12 2019 Monarch Government of Ontario Archived from the original on September 12 2015 Retrieved September 16 2015 monarchscience Akdavis6 wixsite com December 18 2016 Retrieved January 12 2017 Monarchs now listed as an endangered species in Nova Scotia Canada a prelude for things to come elsewhere monarchscience September 30 2019 Retrieved December 12 2019 Crewe Tara L Mitchell Greg W Larrivee Maxim 2019 Size of the Canadian Breeding Population of Monarch Butterflies Is Driven by Factors Acting During Spring Migration and Recolonization Frontiers in Ecology and Evolution 7 doi 10 3389 fevo 2019 00308 ISSN 2296 701X Flockhart D T Tyler Larrivee Maxim Prudic Kathleen L Norris D Ryan June 21 2019 Estimating the annual distribution of monarch butterflies in Canada over 16 years using citizen science data FACETS 4 238 253 doi 10 1139 facets 2018 0011 hdl 10150 633480 Obama President Barack June 20 2014 Presidential Memorandum Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators Office of the Press Secretary Washington D C The White House Retrieved May 2 2018 a b Pollinator Health Task Force May 19 2015 National Strategy to Promote the Health of Honey Bees and Other Pollinators PDF Washington D C The White House Retrieved May 2 2018 a b c EP News Wire Reports May 19 2015 New U S pollinator strategy emphasizes science industry collaboration EPNewswire Archived from the original on September 30 2015 Retrieved January 5 2024 Pollinator Health Task Force May 19 2015 Pollinator Research Action Plan PDF Washington D C The White House pp 1 3 Retrieved January 5 2024 Pollinator Health Task Force June 22 2016 Pollinator Partnership Action Plan PDF Washington D C The White House Retrieved January 5 2024 Multiple sources PBS P100 Facilities Standards For The Public Buildings Service PDF WBDG Whole Building Design Guide Washington D C National Institute of Building Sciences March 1 2015 p 12 Archived PDF from the original on January 8 2024 Retrieved January 8 2024 The P100 is a mandatory standard It is not a guideline textbook handbook training manual nor substitute for technical competence The P100 represents the current state of practice in designing facilities to meet GSA s commitments maximize the efficiency of business processes and comply with the requirements of law PBS P100 Facilities Standards for the Public Buildings Service PDF Landscape Requirements Washington D C U S General Services Administration March 1 2015 pp 40 47 Archived PDF from the original on January 8 2024 Retrieved January 8 2024 Public Law 114 94 114th Congress 129 Stat 1312 1801 PDF United States Government Publishing Office Archived PDF from the original on June 25 2021 Retrieved July 7 2021 a b Multiple sources Sec 1415 Administrative Provisions To Encourage Pollinator Habitat And Forage On Transportation Rights Of Way PDF Public Law 114 94 114th Congress 129 Stat 1421 United States Government Publishing Office Archived PDF from the original on June 25 2021 Retrieved July 7 2021 23 U S Code 319 Landscaping and scenic enhancement Ithaca New York Cornell Law School Legal Information Institute Archived from the original on March 1 2021 Retrieved July 7 2021 c Encouragement of Pollinator Habitat and Forage Development and Protection on Transportation Rights of way In carrying out any program administered by Secretary under this title the Secretary shall in conjunction with willing States as appropriate 1 encourage integrated vegetation management practices on roadsides and other transportation rights of way including reduced mowing and 2 encourage the development of habitat and forage for Monarch butterflies other native pollinators and honey bees through plantings of native forbs and grasses including noninvasive native milkweed species that can serve as migratory way stations for butterflies and facilitate migrations of other pollinators Nadeau Gregory G March 25 2016 Memorandum Improving Habitat for Pollinators Washington D C United States Department of Transportation Federal Highway Administration Retrieved July 7 2021 nbsp This article incorporates text from this source which is in the public domain Multiple sources Fact Sheet The State Acres for Wildlife Enhancement SAFE Initiative PDF Farm Service Agency Conservation Reserve Program United States Department of Agriculture Farm Service Agency December 2019 Archived PDF from the original on September 13 2021 Retrieved October 6 2021 span, wikipedia, wiki, book, books, library,

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