Monarch butterfly

File:Monarch caterpillar (23229).jpg

Monarch butterfly caterpillar

File:Monarch (Danaus plexippus plexippus) underside Piedra Herrada.jpg

D. p. plexippus
Piedra Herrada, Mexico

The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae.<ref name="Agrawal-2017">Template:Cite book</ref> Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown.<ref name="nic.funet.fi"/> It is among the most familiar of North American butterflies and an iconic pollinator,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> although it is not an especially effective pollinator of milkweeds.<ref>Multiple sources:

• Template:Cite journal
• Template:Cite journal</ref> Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of Template:Cvt.<ref name="Garber" /> 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.

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.<ref name="Agrawal-2017" /> 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 have been found in overwintering Mexican sites, as well.<ref name="Groth"/><ref name="JointVenture"/> Non-migratory populations are found further south in the Americas, and in parts of Europe, Oceania, and Southeast Asia.

Etymology

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.<ref name="Jean Ruth Adams"/> The monarch was originally described by Carl Linnaeus in his Systema Naturae of 1758 and placed in the genus Papilio.<ref name="Carl Linnaeus"/> 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,<ref>Multiple sources:

• Template:Cite journal (Cited in Template:Cite book)
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• Template:Cite journal</ref> Anosia was generally considered a subgenus of Danaus.<ref name=smith>Template:Cite journal</ref>

Danaus (Ancient Greek Template:Wikt-lang), a great-grandson of Zeus, was a mythical king in Egypt or Libya, who founded Argos; Plexippus ({{#invoke:Lang|lang}}) 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".<ref>Template:LSJ</ref> In the tenth edition of Systema Naturae, at the bottom of page 467,<ref name="Linnaeus, C. (1758)"/> 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: "{{#invoke:Lang|lang}}" (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 Template:Wikt-lang), 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.<ref>Template:Cite book</ref>

Taxonomy

File:Albino monarch butterfly.jpg

White morph of the monarch in Hawaii called the white monarch

File:Monarch Butterfly G Barker 2023.ogg

Monarch butterfly, Ashbury, Sydney, 2023

Monarchs belong to the subfamily Danainae of the family Nymphalidae. Danainae was formerly considered a separately family Danaidae.<ref name="P.R. Ackery"/> The three species of monarch butterflies are:

• D. plexippus, described by Linnaeus in 1758, is the species known most commonly as the monarch butterfly ranging from North America to northern South America. Its range 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.<ref name=smith/>
• D. cleophile, the Jamaican monarch, described by Jean-Baptiste Godart in 1819, ranges from Jamaica to Hispaniola.<ref name="IUCN"/>

Six subspecies and two color morphs of D. plexippus have been identified:<ref name="nic.funet.fi"/>

• 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.<ref name="Lawrence Gibbs"/>
  • D. p. p. (as yet unnamed) – a color morph lacking some wing vein markings.<ref name="Jacob Groth"/>
• D. p. nigrippus (Richard Haensch, 1909) – South America - as forma: Danais Template:Sic archippus f. nigrippus. Hay-Roe et al. in 2007 identified this taxon as a subspecies<ref name="Hay-Roe, Miriam M. 2007"/>
• 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.<ref name="Lawrence Gibbs"/> However, some taxonomists disagree on these classifications.<ref name=smith/><ref name="Hay-Roe, Miriam M. 2007"/>

Genome

The monarch was the first butterfly to have its genome sequenced.<ref name="Xerces Society"/>Template:Rp 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.<ref>Multiple sources:

• Template:Cite journal
• Template:Cite journal
• Template:Cite news</ref> More recently, the genetic basis of monarch migration and warning coloration has been described.<ref name=Zhan>Template:Cite journal</ref>

No genetic differentiation exists between the migratory populations of eastern and western North America.<ref name="Xerces Society"/>Template:Rp 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.<ref name="Jeffrey L 2011"/>

A 2015 publication identified genes from wasp bracoviruses in the genome of the North American monarch<ref>Template:Cite journal</ref> leading to articles about monarch butterflies being genetically modified organisms.<ref>Multiple sources:

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Life cycle

File:Butterfly life cycle diagram in English.svg

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.<ref name="Xerces Society"/>Template:Rp

Egg

File:Danaus plexippus, Monarch egg.jpg

Egg

File:Monarch depositing egg.webm

Monarch butterfly flying around narrowleaf milkweed, depositing an egg. Played a second time at half speed.

The egg is derived from materials ingested as a larva and from the spermatophores received from males during mating.<ref name=o3>Oberhauser (2004), p. 3</ref> Female monarchs lay eggs singly, most often on the underside of a young leaf of a milkweed plant during the spring and summer.<ref name="NatGeo"/> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Eggs are cream colored or light green, ovate to conical in shape, and about Template:Cvt in size. The eggs weigh less than Template:Cvt each and have raised ridges that form longitudinally from the point to apex to the base. Although each egg is Template:Frac 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.<ref name=o3/> The number of eggs laid by a female, which may mate several times, can reach 1,180.<ref>Template:Cite book</ref>

Eggs take three to eight days to develop and hatch into larvae or caterpillars.<ref name="Xerces Society"/>Template:Rp The offspring's consumption of milkweed benefits health and helps defend them against predators.<ref name="T. Lefevre"/><ref name="Jaap de Roode"/> Monarchs lay eggs along the southern migration route.Template:Sfn

Larva

File:Swallowtail Caterpillar, Monarch Caterpillar & Queen Caterpillar in Florida (27224446333).jpg

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.<ref name="Agrawal-2017" /><ref name=instar>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The first-instar caterpillar that emerges from the egg is pale green or grayish-white, shiny, 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 in 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 Template:Cvt long.<ref name=instar/>

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 Template:Cvt and Template:Cvt long.<ref name=instar/>

File:Monarch caterpillars.webm

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

The third-instar larva has more distinct bands and the two pairs of tentacles become longer. Legs on the thorax differentiate into smaller pairs 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 Template:Cvt long.<ref name=instar/> The fourth-instar larva has a different banding pattern. It develops white spots on the prolegs near its back, and is usually between Template:Cvt long.<ref name=instar/>

File:Monarch butterfly caterpillar on common milkweed.jpg

A monarch caterpillar on milkweed

The fifth-instar larva has a more complex banding pattern and white dots on the prolegs, with small front legs very close to the head. Its length ranges from Template:Cvt.<ref name="Agrawal-2017" /><ref name=instar/> 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 Template:Cvt long (large specimens can reach Template:Cvt) and Template:Cvt wide, and weighs about Template:Cvt, compared to the first instar, which is Template:Cvt long and Template:Cvt 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.<ref name=instar/> A monarch caterpillar can travel up to 10 meters from its milkweed plant to find a safe place to pupate.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In a laboratory setting, the fourth- and fifth-instar caterpillar stages showed aggressive behavior with lower food availability. Attacked caterpillars were found to be attacked when feeding on milkweed leaves, and the caterpillars attacked when foraging for milkweed.<ref>Template:Cite journal</ref> This demonstrates the aggressive behavior of monarch caterpillars due to the availability of milkweed.

Pupa

File:From a caterpillar to a chrysalis….jpg

A caterpillar metamorphosing into a pupa

File:Monarch Butterfly Cocoon 3.jpg

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 few minutes, revealing a green chrysalis (video: https://www.youtube.com/watch?v=QLQmrIUILzc). 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.<ref>Template:Cite journal</ref> 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 Template:Cvt long and Template:Cvt wide, weighing about Template:Cvt. 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).<ref>Multiple sources:

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In 2009, monarchs were reared on the International Space Station, successfully emerging from pupae located in the station's Commercial Generic Bioprocessing Apparatus.<ref>Multiple sources:

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Adult

File:Danaus plexippus emerging from chrysalis 04.jpg

An emergent monarch clinging to its chrysalis shell

The adult emerges from its chrysalis after about two weeks of pupation (video: https://www.youtube.com/watch?v=tQDGizDHVs8 ). 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 many 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.<ref name="monarchlab.org"/>

File:Monarchs flying and sipping.webm

Monarch butterflies flying and sipping nectar from milkweed flowers

The adult's wingspan ranges from Template:Convert.<ref name="Garber"/> 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.<ref name=Braby/> The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants.<ref name="Satterfield"/> Wings size and shape differ between migratory and nonmigratory monarchs. Monarchs from eastern North America have larger and more angular forewings than the western population.<ref name="Xerces Society"/>

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 are thought to convey greater tensile strength and reduce the likelihood of being damaged during migration. Additionally, females had lower wing loading than males, meaning females require less energy to fly.<ref>Template:Cite journal</ref>

Adults are sexually dimorphic. Males are slightly larger than females and have a black spot on a vein on each hindwing. The spots contain androconial 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.<ref name="Xerces Society"/><ref name=Braby/><ref name="ref1"/><ref>Multiple sources:

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The adult thorax has six legs, but like all Nymphalidae, the forelegs are small and held against the body. The butterfly uses only its middle and hind legs when walking and clinging.<ref name="Gene Darby"/>

Adults typically live for 2–5 weeks during their breeding season.<ref name="Xerces Society"/>Template:Rp Larvae growing in high densities are smaller, have lower survival, and weigh less as adults compared with those growing in lower densities.<ref name="D.T. Flockhart"/>

Vision

Physiological experiments suggest that monarch butterflies view the world through a tetrachromatic system.<ref name="Blackiston-2011">Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref>

In addition to these three photoreceptor 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.<ref name="Blackiston-2011" /> The combination of filtered and unfiltered green opsins allows the butterflies to distinguish yellow from orange colors.<ref name="Blackiston-2011" /> The ultraviolet opsin protein has also been detected in the dorsal rim region of monarch eyes. One study suggests that this allows the butterflies to detect ultraviolet-polarized skylight to orient themselves with the sun for their long migratory flight.<ref>Template:Cite journal</ref>

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.<ref name="Cepero-2015" /> Leaf shape is important for oviposition so that the butterflies can ensure their eggs are 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 regarding the ability to learn certain colors; however, no differences are noted between the sexes for monarch butterflies.<ref name="Cepero-2015">Template:Cite journal</ref>

Courtship and mating

File:Monarch butterfly mating.webm

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.<ref name="Emmel, Thomas C."/> Only 30% of mating attempts end in copulation, suggesting that females can avoid mating, though some have more success than others.<ref name="Oberhauser-2004"/><ref name="Frey-1998"/> 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.<ref name="Oberhauser-2009"/>

Females and males typically mate more than once. Females that mate several times lay more eggs.<ref name="Oberhauser-1989"/> Mating for the overwintering populations occurs in the spring, before dispersion. Mating is less dependent on pheromones than in other species in its genus.<ref name="animaldiversity1"/> Male search and capture strategies may influence copulatory success, and human-induced changes to the habitat can influence monarch mating activity at overwintering sites.<ref>Template:Cite journal</ref>

Distribution and habitat

File:String of Monarchs, Pismo Preserve.jpg

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.<ref name="Xerces Society"/>Template:Rp However, no genetic differences between the western and eastern monarch populations exist;<ref name="Jeffrey L 2011"/> reproductive isolation has not led to subspeciation of these populations, as it has elsewhere within the species' range.<ref name="Xerces Society"/>Template:Rp

In the Americas, the monarch ranges from southern Canada through northern South America.<ref name="Agrawal-2017" /> It is also found in Bermuda, the Cook Islands,<ref name="Gerald McCormack"/> Hawaii,<ref name=jas/><ref name="Lincoln P. Brower"/> Cuba,<ref name="Donald Davis"/> and other Caribbean islands,<ref name="Xerces Society"/>Template:Rp the Solomons, New Caledonia, New Zealand,<ref name="monarch.org.nz"/> Papua New Guinea,<ref name="NewsAdvance.com"/> Australia, the Azores, the Canary Islands, Madeira, continental Portugal, Gibraltar,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> the Philippines, and Morocco.<ref name="Miguel Pais"/> It appears in the UK in some years as an accidental migrant.<ref name="Simon Coombes"/>

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 survival.<ref name=rcgt>Cech, Rick and Tudor, Guy (2005). Butterflies of the East Coast. Princeton University Press, Princeton, NJ. Template:ISBN</ref><ref name=isc>Iftner, David C.; Shuey, John A. and Calhoun, John C. (1992). Butterflies and Skippers of Ohio. College of Biological Sciences and The Ohio State University. Template:ISBN</ref> On the East Coast of the United States, they have overwintered as far north as Virginia Beach, Virginia.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name="Robert Michael Pyle"/> 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.<ref name="Sue Halpern"/>

Larval host plants

File:Image of Asclepia currasvica.jpg

Asclepias curassavica

The host plants used by the monarch caterpillar include:

File:Swamp Milkweed Asclepias incarnata Flowers Closeup 2800px.jpg

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

• Araujia sericifera – white bladderflower<ref>Multiple sources:
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• Asclepias angustifolia – Arizona milkweed<ref name="Monarch Joint Venture">{{#invoke:citation/CS1|citation

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• Asclepias albicans – whitestem milkweed<ref>Multiple sources:
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• Asclepias asperula – antelope horns milkweed<ref name="Monarch Joint Venture"/>
• Asclepias californica – California milkweed<ref name="Monarch Joint Venture"/>
• Asclepias cordifolia – heartleaf milkweed<ref name="Monarch Joint Venture"/>
• Asclepias curassavica - blood flower<ref>Multiple sources:
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• Asclepias eriocarpa – woollypod milkweed<ref name="Monarch Joint Venture"/>
• Asclepias erosa – desert milkweed<ref name="Monarch Joint Venture"/>
• Asclepias exaltata – poke milkweed<ref name="Monarch Joint Venture"/><ref>Multiple sources:
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• Asclepias fascicularis – Mexican whorled milkweed<ref name="Monarch Joint Venture"/>
• Asclepias hirtella - tall green milkweed<ref>Multiple sources:
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• Asclepias humistrata – sandhill/pinewoods milkweed<ref name="Monarch Joint Venture"/>
• Asclepias incarnata – swamp milkweed<ref>Multiple sources:
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• Asclepias lanceolata - fewflower milkweed<ref>Multiple sources:
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• Asclepias linaria – pineneedle milkweed<ref>Multiple sources
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• Asclepias meadii - Meade's milkweed<ref>Multiple sources:
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• Asclepias nivea – Caribbean milkweed<ref>{{#invoke:citation/CS1|citation

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• Asclepias oenotheroide – zizotes milkweed<ref name="Monarch Joint Venture"/>
• Asclepias perennis – aquatic milkweed<ref name="Monarch Joint Venture"/>
• Asclepias quadrifolia - four-leaved milkweed<ref>Multiple sources:
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• Asclepias speciosa – showy milkweed<ref name="Monarch Joint Venture"/><ref>Multiple sources:
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• Asclepias subulata – rush milkweed<ref name="Monarch Joint Venture"/>
• Asclepias sullivantii - prairie milkweed<ref>Multiple sources:
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• Asclepias syriaca – common milkweed<ref name="Common Milkweed">Multiple sources:
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• Asclepias tuberosa – butterfly weed<ref name="Monarch Joint Venture"/>
• Asclepias variegata – white milkweed<ref name="Monarch Joint Venture"/>
• Asclepias verticillata – whorled milkweed<ref name="Monarch Joint Venture"/>
• Asclepias vestita – woolly milkweed<ref name="Monarch Joint Venture"/>
• Asclepias viridis – green antelopehorn milkweed<ref name="Monarch Joint Venture"/><ref>Multiple sources:
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• Calotropis gigantea – crown flower<ref>{{#invoke:citation/CS1|citation

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• Calotropis procera - giant milkweed<ref>Multiple sources:
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• Cynanchum laeve – sand vine milkweed<ref>Butterfly Gardening. kansasnativeplants.com</ref>
• Gomphocarpus fruticosus – swan plant<ref>Multiple sources:
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• Gomphocarpus physocarpus – balloon plant<ref>Multiple sources:
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• Sarcostemma clausa – white vine<ref name=jas/><ref name=dlw/>

Template:Div col end The eastern monarch migration largely depends upon only three of these species: Asclepias syriaca, A. viridis, and A. asperula.<ref name=Taylor1>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, Asclepias curassavica, or tropical milkweed, is often planted as an ornamental in butterfly gardens. Year-round plantings in the USA are controversial and criticized, as they may cause new overwintering sites along the U.S. Gulf Coast, leading to year-round breeding of monarchs.<ref>Template:Cite journal</ref> This is thought to adversely affect migration patterns and to cause a dramatic buildup of the dangerous parasite, Ophryocystis elektroscirrha.<ref>Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref>

Adult food sources

File:Monarch Butterfly Danaus plexippus on Echinacea purpurea 2800px.jpg

Nectaring on purple coneflower (Echinacea purpurea)

Although larvae eat only milkweed, adult monarchs feed on the nectar of many plants, including:<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

• Apocynum cannabinum – Indian hemp
• Asclepias spp. – milkweed
• Buddleja davidii - butterfly-bush<ref>Multiple sources:
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• 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<ref name="isc"/>

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 the pavement.<ref name=isc/>

Flight and migration

File:Monarch butterflies (Danaus plexippus plexippus) on Oyamel fir (Abies religiosa) Piedra Herrada.jpg

Overwintering on Oyamel fir (Abies religiosa)
Piedra Herrada, Mexico

File:Migrating monarch butterflies on pine tree.jpg

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.<ref name="Agrawal-2017" /> This is a multi-generational migration, with individual monarchs only making part of the full journey.<ref>Template:Cite journal</ref> 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 populations east of the Rocky Mountains, which mostly overwinter in central Mexico, may return the following spring as far north as Texas and Oklahoma before producing offspring to carry the journey northward. The second, third, and fourth generations return to their northern locations in the United States and Canada later in the spring and far into the summer.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Captive-raised monarchs appear capable of migrating to overwintering sites in Mexico,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> though they have a much lower migratory success rate than do wild monarchs (see section on captive-rearing below).<ref name=steffy>Template:Cite journal</ref> Monarch overwintering sites have been discovered recently in Arizona.<ref> Template:Cite news</ref> Monarchs from the eastern US generally migrate longer distances than monarchs from the western US.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Since the 1800s, monarchs have spread globally, and there are now many non-migratory populations.<ref>Template:Cite journal</ref>

Flight speeds of adults are around Template:Cvt. Monarch butterflies embark on a marvelous migratory phenomenon. They travel between 1,200 and 2,800 miles or more from the northeast United States, and southeast Canada to the mountain forests in central Mexico, where they find the right climate conditions to hibernate from the beginning of November to mid-March.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Interactions with predators

In both caterpillar and butterfly forms, 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Larvae feed exclusively on milkweed and consume protective cardiac glycosides. Toxin levels in the Asclepias species vary. Not all monarchs are unpalatable, but exhibit Batesian or automimics. Cardiac glycoside levels are higher in the abdomen and wings. Some predators can differentiate between these parts and consume the most palatable ones.<ref name="Barbosa">Template:Cite book</ref>

Butterfly weed (A. tuberosa) lacks significant amounts of cardiac glycosides (cardenolides) but instead contains other types of toxic glycosides, including pregnanes.<ref>Multiple sources:

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• Template:Cite journal
• Template:Cite journal</ref> 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.<ref name=Abugattas>Multiple sources:
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• Template:Cite journal</ref> Some other milkweeds have similar characteristics.<ref>Template:Cite journal</ref>

Types of predators

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 can eat the monarch through an exaptation of its feeding behavior that gives it the ability to identify cardenolides by taste and reject them.<ref name="Brower1988">Template:Cite journal</ref> The black-headed grosbeak, though, has developed an insensitivity to secondary plant poisons that allows it to ingest monarchs without vomiting.<ref>Template:Cite journal</ref> 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% indicating that monarch aposematism has a legitimate purpose.<ref name="Brower1988" /> 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.<ref>Template:Cite journal</ref> Known bird predators include brown thrashers, grackles, robins, cardinals, sparrows, scrub jays, and pinyon jays.<ref name="Barbosa" />

File:Chinese Mantis, Sand Ridge State Forest, Mason County, IL imported from iNaturalist photo 2924073.jpg

Chinese mantis feeding on a monarch butterfly. The species also feeds on monarch caterpillars, being resistant to their toxins and gutting them before consumption to remove most of the toxins.<ref>Template:Cite journal</ref>

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.<ref>Template:Cite journal</ref>

File:Monarch Predators.webm

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 can eat monarchs.<ref name="mammalspecies">Template:Cite journal</ref> 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.<ref name="rcgt" /><ref name="mammalspecies"/>

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).<ref>Template:Cite journal</ref> The Chinese mantis (Tenodera sinensis) will consume the larvae once the gut is removed thus avoiding cardenolides.<ref>Template:Cite journal</ref> Predatory wasps commonly consume larvae.<ref>Template:Cite journal</ref> 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.Template:Sfn

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

Aposematism

File:Oleandrin-skeletal.svg

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.<ref name="animaldiversity1" /> 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.<ref name="Karageorgi-2019">Template:Cite journal</ref> By ingesting a large number of plants in the genus Asclepias, primarily milkweed, monarch caterpillars can sequester cardiac glycosides, or more specifically cardenolides, which are steroids that act in heart-arresting ways similar to digitalis.<ref name=parsons_digitalis>Template:Cite journal</ref> It has been found that monarchs can sequester cardenolides most effectively from plants of intermediate cardenolide content rather than those of high or low content.<ref name=malcolm_evolutionary>Template:Cite journal</ref> Three mutations that evolved in the monarch's Na+/ K+-ATPase were found to be sufficient together to confer resistance to dietary cardiac glycosides.<ref name="Karageorgi-2019" /> 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<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> were completely resistant to dietary ouabain, a cardiac glycoside found in Apocynaceae, and even sequestered some through metamorphosis, like the monarch.<ref name="Karageorgi-2019" />

Different milkweed species have variable effects on parasite growth, virulence, and transmission.<ref name=deRood_Virulence>Template:Cite journal</ref> 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.<ref name="deRood_Virulence" /> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

After the caterpillar becomes a butterfly, the toxins shift to different body parts. Since many birds attack the butterfly's wings, having three times the cardiac glycosides in the wings leaves predators with a foul taste and may prevent them from ever ingesting the butterfly's body.<ref name="parsons_digitalis" /> To combat predators that remove the wings only to ingest the abdomen, monarchs keep the most potent cardiac glycosides in their abdomens.<ref>Template:Cite journal</ref>

Mimicry

File:Monarch Viceroy Mimicry Comparison.jpg

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 more unpalatable than the monarch, making this a case of Müllerian mimicry.<ref name=Ritland>Template:Cite journal</ref>

Human interaction

The monarch is the state insect of Alabama,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Idaho,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Illinois,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Minnesota,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Texas,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Vermont,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and West Virginia.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Legislation was introduced to make it the national insect of the United States,<ref>Template:Cite news</ref> but this failed in 1989<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and again in 1991.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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. <ref>{{#invoke:citation/CS1|citation |CitationClass=web }} </ref>

A 2012 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.<ref name="Fleet">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Sanctuaries and reserves have been created at overwintering locations in Mexico and California to limit habitat destruction. These sites can generate significant tourism revenue.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, with less tourism, monarch butterflies may exhibit higher survival rates, as butterflies in tourist isolated areas have shown increases in protein content, immune response and oxidative defense.<ref>Template:Cite journal</ref>

Organizations and individuals participate in tagging programs. Tagging information is used to study migration patterns.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The 2012 novel by Barbara Kingsolver, Flight Behavior, deals with the fictional appearance of a large population in the Appalachians.<ref>Template:Cite book</ref>

Captive rearing

File:Monarca Butterflies in a Paladarium.jpg

Captive butterflies in Parque de la Reserva, Lima, Peru

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Memorial services for the September 11 attacks include the release of captive-bred monarchs.<ref>Multiple sources:

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• Template:Cite news</ref> Monarchs are used in schools and nature centers for educational purposes.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> Many homeowners raise monarchs in captivity as a hobby and for educational purposes.<ref name=watch>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Monarchs born in captivity are friendly to humans and are a pleasure to play with (https://www.youtube.com/watch?v=3brZuY-yWh0). They may need to be taught how to feed on artificial food (https://www.youtube.com/shorts/5KH3NLDaRvU).

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.<ref>Multiple sources:

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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 to "boost the monarch population". Some individuals, such as one in Linn County, Iowa, have reared thousands of monarchs at the same time.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref>Rearing Monarchs Responsibly: A conservationist's guide to raising monarchs for science and education Template:Webarchive. Monarch Joint Venture, University of Minnesota</ref> 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 parasite spores can quickly contaminate all housing equipment so all subsequent monarchs reared in the same containers become infected. One researcher stated that rearing more than 100 monarchs constitutes "mass rearing" and should not be done.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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 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.<ref name=steffy/>

A 2019 study shed light on captive-reared monarchs' fitness by testing reared and wild monarchs on a tethered flight apparatus that assessed navigational ability.<ref>Template:Cite journal</ref> In that study, monarchs that were reared to adulthood in artificial conditions showed a reduction in navigational ability. This happened even with monarchs 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".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

An unpublished study in 2019 compared the behavior of captive-reared versus wild monarch larvae.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The study showed that reared larvae exhibited more defensive behavior than wild larvae. The reason for this is unknown, but it could relate to reared larvae being frequently handled and/or disturbed.

Threats

In February 2015, the United States Fish and Wildlife Service (USFWS) 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 partly to a loss of milkweed caused by herbicides that farmers and homeowners had used.<ref>Template:Cite news</ref>

A 2017 report included mention of the new ethanol-in-gasoline standards as reducing the amount of acreage left fallow in the U.S. midwest: "Federal policies such as the Ethanol Fuel Standards (Renewable Fuel Standard), crop insurance, and waning Farm Bill support for CRP reduce support for integrated agro-ecological landscapes capable of sustaining both food production and monarch habitat, principally because these policies promote row crops over mixed, herbaceous perennial vegetation."<ref name="ERL-2017">Template:Cite journal</ref>

In 2018, a study correlated monarch butterfly decline to the fact that 95% of corn and soybean crops grown in the United States used genetically modified seeds resistant to the herbicide glyphosate. This meant that instead of spreading the herbicide only before seed planting, farmers could spread the herbicide a second time by air when weeds had begun to challenge the crops. Air application of the herbicide meant that the unplowed margins between the field and road that previously supported milkweed and a range of nectar flowers were now greatly diminished.<ref name=phys-org-2018>Template:Cite news</ref>

By 2024, the USFWS calculated that the eastern butterflies had declined by approximately 80 percent since the 1980s. The western population was more imperiled, declining by 95 percent.<ref name="phys-org-monarch-2024">Template:Cite news</ref> According to the USFWS, the species faces a host of threats, including the loss and degradation of its breeding, migratory, and overwintering habitats, exposure to insecticides, and the growing impacts of climate change.<ref name="phys-org-monarch-2024" />

Western monarch populations

File:Western monarch populations 1997-2013.JPG

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 by 86% in 2018, going from millions to tens of thousands of butterflies.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The society's annual 2020–2021 winter count showed a significant decline in the California population. One Pacific Grove site had no monarch butterflies. A primary explanation for this was the destruction of the butterfly's milkweed habitats.<ref name="Xerces Society"/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This particular population is believed to comprise less than 2000 individuals, Template:As of.<ref name="Dellinger 2022">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Eastern and midwestern monarch populations

A 2016 study attributed the previous decade's 90% decline in overwintering numbers of the eastern monarch population primarily to the loss of breeding habitat and milkweed. The publication's authors stated that an 11%–57% probability existed that this population will become "quasi-extinct" over the next 20 years (i.e. unable to sustain a stable population).<ref name=Semmens>Template:Cite journal</ref> Other threats identified in the study include climate change, insecticides, and disease.<ref name=Semmens/>

Chip Taylor, the director of Monarch Watch at the University of Kansas, stated in 2013 that the Midwest milkweed habitat "is virtually gone" with 120–150Template:Nbspmillion acres lost.<ref name=yale>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Wines">Wines, Michael (March 13, 2013). "Monarch Migration Plunges to Lowest Level in Decades". The New York Times.</ref> However, he predicted in 2024 that in the immediate future and perhaps into the next two decades, the eastern monarch butterfly population will be relatively stable because it is not presently on a continuous downward trend as it was from 2000-2006.<ref name=Taylor1/> To help fight the population decline, Monarch Watch encourages the planting of "Monarch Waystations".<ref name=watch/>

Habitat loss due to herbicide use and genetically modified crops

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.<ref name=Semmens/> 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.<ref>Template:Cite journal</ref><ref name="Brennen">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, a 2018 study has suggested that the decline in milkweed predates the arrival of GM crops.<ref>Template:Cite journal</ref>

Losses during migration

File:Monarch butterfly in zinnia patch.jpg

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

Eastern and midwestern monarchs are experiencing problems reaching Mexico. Many monarch researchers have cited recent evidence from long-term citizen science data that shows that the number of breeding (adult) monarchs has not declined in the last two decades.<ref name="Ries 2015">Template:Cite journal</ref><ref name="Inamine 2016">Template:Cite journal</ref><ref name="ReferenceA">Template:Cite journal</ref>

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.<ref name="monarchscience">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref>Template:Cite journal</ref>

Importance of overwintering habitat

File:Danaus plexippus overwintering area 2018.png

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

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 fir trees; however, organized criminals have repeatedly crushed such efforts in the name of very short-term financial gain.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The oyamel is a major species of evergreen on which the overwintering butterflies spend a significant time during their winter diapause, or suspended development.<ref>Paz, Fátima (June 18, 2014). "En espera de aprobación de la Profepa por tala ilegal en la Reserva de la Mariposa Monarca" Template:Webarchive. cambiodemichoacan.com.mx.</ref>

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 recent and projected population declines.<ref name="University of Guelph">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Western monarch populations have rebounded slightly since 2014 with the Western Monarch Thanksgiving Count <ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> tallying 335,479 monarchs in 2022. The population still has much to go for a full recovery.

Parasites

File:Monarch chrysalis - Danaus plexippus and Pteromalid Wasp, Meadowood Farm SRMA, Mason Neck, Virginia - 29789548882.jpg

Pteromalus cassotis on monarch chrysalis

Parasites include the tachinid flies Sturmia convergens,<ref>Template:Cite journal</ref> Compsilura concinnata,<ref name=Oberhauser>Template:Cite journal</ref> Madremyia saundersii,<ref name=Oberhauser/> Hyphantrophaga virilis,<ref name=Oberhauser/> Nilea erecta,<ref name=Oberhauser/> and Lespesia archippivora.<ref name=Oberhauser/> Lespesia-parasitized butterfly larvae suspend, but die prior to pupation. The fly's maggot lowers to the ground, forms a brown puparium, and then emerges as an adult.<ref name = Brewer>Template:Cite journal</ref>

Pteromalid wasps, specifically Pteromalus cassotis, parasitize monarch pupae.<ref name="pteromalidae">Template:Cite journal</ref> 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,<ref name="pteromalidae" /> 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.<ref name = Brewer/>

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 bodies 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.<ref>Template:Cite journal</ref>

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.<ref name="Bartel Ober">Template:Cite journal</ref> Owners of commercial butterfly-breeding operations claim that they take steps to control this parasite in their practices,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> although this claim is doubted by many scientists who study monarchs.<ref>Template:Cite book</ref>

Confusion of host plants

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.<ref>Invasive species alert: Black swallow-wort (Cynanchum louisea) and pale swallow-wort (Cynanchum rossicum) Template:Webarchive. monarchjointventure.org</ref>

Climate

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 Template:Cvt can be lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate."<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> If a monarch's body temperatures is below Template:Cvt, a monarch cannot fly. To warm up, they sit in the sun or rapidly shiver their wings to warm themselves.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref>Template:Cite journal</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref>Template:Cite journal</ref> 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.<ref name="Climate change, pesticides put monarch butterflies at risk of extinction">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Conservation status

The number of monarchs overwintering in Mexico has shown a long-term downward trend. Since 1995, coverage numbers have been as high as Template:Convert during the winter of 1996–1997, but on average about Template:Convert. Coverage declined to its lowest point to date (Template:Convert) during the winter of 2013–2014, but rebounded to Template:Convert in 2015–2016. The average population of monarchs in 2016 was estimated at 200Template:Nbspmillion. Historically, on average there are 300Template:Nbspmillion monarchs. The 2016 increase was attributed to favorable breeding conditions in the summer of 2015. However, coverage declined by 27% to Template:Convert 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.<ref>Multiple sources:

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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 as an endangered species.<ref name="Larson">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, a petition in 2023 resulted in its status being changed to "vulnerable".<ref name="IUCN"/>

The monarch butterfly is not listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora or protected specifically under U.S. domestic laws.<ref name="fws.gov" />

On August 14, 2014, the Center for Biological Diversity and the Center for Food Safety petitioned the United States Secretary of the Interior through the USFWS to protect the Danaus plexippus plexippus subspecies of the monarch butterfly as a threatened species under the Endangered Species Act.<ref name="Xerces Society"/> On December 31, 2014, the USFWS initiated a review of the status of the butterfly to determine whether the petitioned action was warranted, with a due date for the submission of information of March 3, 2015, later extended to December 15, 2020.<ref>Multiple sources:

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On December 17, 2020, the USFWS published in the Federal Register a notice in which it stated that adding the butterfly to the list of threatened and endangered species was "warranted-but-precluded" because budgetary limitations required it to devote its resources to species with higher priorities for listing. The notice stated that the USFWS had 422 12-month petition findings for domestic species yet to be initiated and completed at the beginning of Fiscal Year 2020 (October 1, 2019).<ref>Multiple sources:

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On June 27, 2023, the USFWS published in the Federal Register a Notice of Proposed Rulemaking for a rule that would give the butterfly a listing priority number (LPN) of 8 for adding its species to that list.<ref>Multiple sources:

• Template:Cite journal
• Ibid., Monarch Butterfly, p. 41570.</ref> LPNs range from 1 to 12 (the lower the LPN, the higher the listing priority).<ref>Ibid., Previous CNORs, p. 41561. "We have been publishing CNORs since 1975. The most recent was published on May 3, 2022 (87 FR 26152). On September 21, 1983, we published guidance for assigning a listing priority number (LPN) for each candidate species (48 FR 43098). Using this guidance, we assign each candidate an LPN of 1 to 12, depending on the magnitude of threats, immediacy of threats, and taxonomic status; the lower the LPN, the higher the listing priority (that is, a species with an LPN of 1 would have the highest listing priority)."</ref>

On December 12, 2024, the USFWS published in the Federal Register a proposed rule that would list the butterfly as a threatened species and would designate the butterfly's critical habitat per the provisions of the Endangered Species Act. The USFWS estimated in the proposed rule that the probability of extinction in the foreseeable future (60 years) is 56-74 percent for the eastern monarch migratory population and 99 percent for the western migratory population. The proposed rule designated seven areas near California's Pacific coast as "critical habitat units" for monarch butterflies. The USFWS accepted comments on the proposed rule until March 12, 2025.<ref>Template:Cite journal</ref> On March 19, 2025, the USFWS reopened the comment period on the proposed rule until May 19, 2025.<ref>Template:Cite journal</ref>

In December 2023, the Government of Canada listed the monarch as an endangered species under the federal Species at Risk Act. The listing protects the butterfly on Canadian federal lands by making it illegal to kill, hurt, catch or remove a monarch egg, caterpillar, chrysalis or adult when on land that the Canadian federal government owns and/or administers. These include Canadian national parks, national wildlife areas, military bases and First Nations reserves. It is also illegal to possess, collect, buy, sell, or trade an individual monarch or any part or derivative of an individual when on that land. The Canadian government must prepare a recovery strategy and one or more action plans for the species to outline the work that can be done to conserve the species. The strategy must identify the critical habitat necessary for the monarch to survive and recover in Canada.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In Ontario, Canada, the monarch butterfly is listed as a species of special concern.<ref name="Monarch Butterfly Status in Ontario"/> In Nova Scotia, the monarch is listed as endangered at the provincial level, Template:As of. This decision (as well as the Ontario decision) is based on a presumption that the overwintering colony declines in Mexico create declines in the breeding range in Canada.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Two recent studies have been conducted examining long-term trends in monarch abundance in Canada, using either butterfly atlas records<ref>Template:Cite journal</ref> or citizen science butterfly surveys,<ref>Template:Cite journal</ref> and neither shows evidence of a population decline in Canada.

Conservation efforts

Template:See also Although the numbers of breeding monarchs in eastern North America have not decreased, reports of declining numbers of overwintering butterflies have inspired efforts to conserve the species.<ref name="Ries 2015"/><ref name="Inamine 2016"/><ref name="ReferenceA"/>

Federal actions

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.<ref>{{#invoke:citation/CS1|citation

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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.<ref>Multiple sources:

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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:

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Many of the priority projects that the National Strategy identified focused on the I-35 corridor, which extends for Template:Convert 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.<ref name=strategy/><ref name=Newswire/>

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.<ref name=Newswire/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In May 2015, the U.S. Department of Agriculture (USDA) and the U.S. Department of the Interior (USDI) issued a 52-page document entitled "Pollinator-Friendly Best Management Practices for Federal Lands". The document consolidated general information about the practices and procedures to use when considering pollinator needs in project development and management of Federal lands that are managed for native diversity and multiple uses. The document also contained a series of actions to be considered when determining those lands best suited for restoration and rehabilitation of monarch habitat. These included an assurance that native wildflowers are available, diverse, and abundant to provide nectar for monarchs and an assurance that milkweed species that female monarchs prefer for egg laying are available or will be planted. The document identified those milkweed species for each of seven regions within the United States.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

On December 4, 2015, President Obama signed into law the Fixing America's Surface Transportation (FAST) Act (Pub. L. 114-94).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name=Code>Multiple sources:

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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.<ref name=Code/>

In February 2016, the Office of the U.S. Secretary of the Interior issued a memorandum containing an attachment entitled "Strategy for Implementing Pollinator-Friendly Landscaping Design and Maintenance at Department of the Interior Sites". The attachment described specific actions that would address the incorporation of pollinator-friendly landscaping design and maintenance into new construction and major renovations, existing sites, contracts, leases and occupancy agreements, and education/outreach programs. The memorandum containing the attachment directed the USDI's bureaus and offices (which include the Fish and Wildlife Service, the Bureau of Land Management, and the National Park Service) to implement those actions to the extent that they are appropriate for and consistent with, the mission and function of the facility/site.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In June 2016, the Pollinator Health 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The USDA's Farm Service Agency helps increase U.S. populations of the 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 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.<ref>Multiple sources:

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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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Other actions

Agriculture companies and other organizations are being asked to set aside unsprayed areas 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.<ref name="Brennen"/><ref name=Tennessee>Multiple sources:

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National Cooperative Highway Research Program report

In 2020, the National Cooperative Highway Research Program (NCHRP) 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 habitats for monarch butterflies in their road rights-of-way.<ref>Multiple sources:

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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 annually.<ref name="monarchscience"/> Also, some evidence indicates that monarch larvae living near roads experience physiological stress conditions, as evidenced by elevations in their heart rate.<ref>Template:Cite journal</ref>

The NCHRP 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.<ref name=NCHRP3>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Nevertheless, the report concluded:

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Butterfly gardening and monarch waystations

File:Monarch Butterfly waystation sign.jpg

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.<ref>Multiple sources:

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|CitationClass=web }}</ref> 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.<ref>Multiple sources:

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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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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 ensure 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 antelope horn milkweed (A. viridis), where it grows in the Southern Great Plains and the Western United States.<ref name="Monarch Joint Venture"/><ref>Multiple sources:

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|CitationClass=web }}</ref> Further, the seeds of A. syriaca and some other milkweeds need periods of cold treatment (cold stratification) before they will germinate.<ref>Multiple sources:

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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 Template:Convert layer of straw mulch.<ref>Multiple sources:

• Template:Cite book
• Template:Cite journal</ref> 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.<ref>Template:Cite book</ref>

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The plant has rough leaves and a layer of trichomes, which may inhibit oviposition or decrease a female's ability to sense leaf chemicals.<ref name=Gomez>{{#invoke:citation/CS1|citation |CitationClass=web }}.Template:Self-published inline</ref><ref>Template:Cite journal</ref> The plant's low levels of cardenolides may also deter monarchs from laying eggs on the plant. <ref>Multiple sources:

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|CitationClass=web }}</ref> While A. tuberosaTemplate:'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.<ref name=Gomez/>

Breeding monarchs prefer to lay eggs on swamp milkweed (A. incarnata) in the midwest.<ref>Template:Cite journal</ref> 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.<ref name=survival>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Although A. incarnata plants can survive up to 20 years, most live only two to five years in gardens. The species is not shade-tolerant and is not a good vegetative competitor.<ref name=survival/>

See also

• Butterfly house
• Lepidoptera migration
• Peninsula Point Light, Michigan

External links

• Australian Museum fact sheet on monarch butterflies
• Mission Monarch (Canada)
• Monarch butterfly metamorphosis: time-lapse video (2:42 minutes)
• Monarch butterfly on the UF / IFAS Featured Creatures website
• Monarch Joint Venture – Partnering Across the U.S. to Conserve the Monarch Butterfly Migration
• Monarch migration maps
• Monarch Watch
• PBS Nova documentary "The Incredible Journey of the Butterflies"
• USGS description of monarch butterfly
• Monarch butterfly data at NatureServe Explorer