Monarch butterfly

Milkweed butterfly in the family NymphalidaeTemplate:SHORTDESC:Milkweed butterfly in the family Nymphalidae

The **monarch butterfly** or simply **monarch** (*Danaus plexippus*) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include **milkweed**, **common tiger**, **wanderer**, and **black veined brown**. It may be the most familiar North American butterfly, and is considered an iconic pollinator species. Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9–10.2 cm (3+1⁄2–4 in) 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 migration from the northern and central United States and southern Canada to Florida and Mexico. During the fall migration, monarchs cover thousands of miles, with a corresponding multi-generational return north. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern California but has been found in overwintering Mexican sites as well. Monarchs have been bred on the International Space Station. In 2009, an investigation in space took place. The monarch butterfly successfully emerged from its pupa located in the station's Commercial Generic Bioprocessing Apparatus.

## Taxonomy

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. The monarch was originally described by Carl Linnaeus in his *Systema Naturae* of 1758 and placed in the genus *Papilio*. In 1780, Jan Krzysztof Kluk used the monarch as the type species for a new genus, *Danaus*.

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". In the 10th edition of *Systema Naturae*, at the bottom of page 467, 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.

There are three species of monarch butterflies:

* *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 and can be found in 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 2 mya, 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.
* *D. cleophile*, the Jamaican monarch, described by Jean-Baptiste Godart in 1819, ranges from Jamaica to Hispaniola.

Six subspecies and two color morphs of *D. plexippus* have been identified:

* *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.
	+ *D. p. p.* (as yet unnamed) – a color morph lacking some wing vein markings.
* *D. p. nigrippus* (Richard Haensch, 1909) – as *forma*: *Danais* [*sic*] *archippus* f. *nigrippus*. Hay-Roe *et al.* in 2007 identified this taxon as a subspecies:
* *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 percentage of the white morph in Oahu is nearing 10%. On other Hawaiian islands, the white morph occurs at a relatively low frequency. White monarchs (*nivosus*) have been found throughout the world, including Australia, New Zealand, Indonesia, and the United States. However, some taxonomists disagree on these classifications.

Monarchs belong in the subfamily Danainae of the family Nymphalidae. Danainae was formerly considered a separately family Danaidae.

## Genome

The monarch was the first butterfly to have its genome sequenced. 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. More recently, the genetic basis of monarch migration and warning coloration has been described.

There is no genetic differentiation between the migratory populations of eastern and western North America. Recent research has identified the specific areas in the genome of the monarch that regulate migration. There appears to be no genetic difference between a migrating and nonmigrating monarch but the gene is expressed in migrating monarchs but not expressed in nonmigrating monarchs.

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

## Life cycle

### Metamorphosis

Like all Lepidoptera, monarchs undergo complete metamorphosis. 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.. The monarch's life cycle has four phases: egg, larva, pupa and adult.

#### Egg

The egg is derived from materials ingested as a larva and from the spermatophores received from males during mating. Female monarchs lay eggs singly, most often on the underside of a young leaf of a milkweed plant during the spring and summer. 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.

Eggs are cream colored or light green, ovate to conical in shape, and about 1.2×0.9 mm in size. The eggs weigh less than 0.5 mg 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. The number of eggs laid by a female, who may mate several times, can reach 1,180.

Eggs take 3 to 8 days to develop and hatch into larva or caterpillars. The offspring's consumption of milkweed benefits health and helps defend them against predators. Monarchs will lay eggs along the southern migration route.

#### Larva

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.

**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 long.

**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 but 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 and 1 cm long.

**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 long.

**The fourth instar** has a different banding pattern. It develops white spots on the prolegs near the back of the caterpillar. It is usually between 1.5 and 2.5 cm long.

**The fifth instar** has a more complex banding pattern and white dots on the prolegs, with front legs that are small and very close to the head. Fifth instar larvae often chew a shallow notch in the petiole of the leaf they are eating, which causes the leaf to fall into a vertical position. Its length ranges from 2.5 to 4.5 cm.

As the caterpillar completes its growth, it is 4.5 cm long (large specimens can reach 5 cm) and 7 to 8 mm wide, and weighs about 1.5 grams, compared to the first instar, which was 2 to 6 mm long and 0.5 to 1.5 mm 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.

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 caterpillar attacked when it was foraging for milkweed. This demonstrates the aggressive behavior of monarch caterpillars due to the availability of milkweed.

#### Pupa

To prepare for the pupa 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 hindlegs and hangs upside down, in the form of the letter J. After "J-hanging" for about 12–16 hours, it will suddenly straighten out its body and go 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. 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 (1") long and 10–12 mm (3/8–7/16") wide, weighing about 1.2 grams. 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).

#### Adult

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

The adult's wingspan ranges from 8.9 to 10.2 centimetres (3.5–4.0 in). The upper sides of the wings are tawny orange, the veins and margins are black, and there are two series of small white spots 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. The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants. Wings size and shape differ between migratory and non-migratory monarchs. Monarchs from eastern North America have larger and more angular forewings than those in the western population.

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.

Adults are sexually dimorphic. Males are slightly larger than females>and have a black spot on a vein on each hind wing. 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.

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

Adults typically live for two to five weeks during their breeding season. Larvae growing in high densities are smaller, have lower survival, and weigh less as adults compared with those growing in lower densities.

### Pictorial life cycle

Stages of developmentEggEmergent caterpillar (first instar)Caterpillar on milkweedCaterpillar feeding on tropical milkweedCaterpillar feeding on *Asclepias physocarpa*Awaiting pupationUndergoing pupationCompleting pupationChrysalisChrysalis prior to emergence of adultEmerging from chrysalisEmergent adult clinging to its exuviaeMatingLaying egg
## Flight

Monarch flight has been described as "slow and sailing", with an estimated flight speed of 9 km/h (6 mph).

## Courtship and mating

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. Only 30% of mating attempts end in copulation, suggesting that females may be able to avoid mating, though some have more success than others. During copulation, a male transfers his spermatophore to a female. Along with sperm, the spermatophore provides a female with nutrition, which aids her in egg laying. An increase in spermatophore size increases the fecundity of female monarchs. Males that produce larger spermatophores also fertilize more females' eggs.

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

## Distribution and habitat

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

In the Americas, the monarch ranges from southern Canada through northern South America. It has also been found in Bermuda, Cook Islands, Hawaii, Cuba, and other Caribbean islands the Solomons, New Caledonia, New Zealand, Papua New Guinea, Australia, the Azores, the Canary Islands, Madeira, continental Portugal, Gibraltar, the Philippines, and Morocco. It appears in the UK in some years as an accidental migrant.

Overwintering populations of *D. plexippus 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. On the East Coast of the United States, they have overwintered as far north as Lago Mar, Virginia Beach, Virginia. 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. While breeding, monarch habitats can be found in agricultural fields, pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides – anywhere where there is access to larval host plants.

## Larval host plants

The host plants used by the monarch caterpillar include:

* *Asclepias angustifolia* – Arizona milkweed
* *Asclepias asperula* – antelope horns milkweed
* *Asclepias californica* – California milkweed
* *Asclepias cordifolia* – heartleaf milkweed
* *Asclepias curassavica*
* *Asclepias eriocarpa* – woolly pod milkweed
* *Asclepias erosa* – desert milkweed
* *Asclepias exaltata* – poke milkweed
* *Asclepias fascicularis* – Mexican whorled milkweed
* *Asclepias humistrata* – sandhill/pinewoods milkweed
* *Asclepias incarnata* – swamp milkweed
* *Asclepias nivea* – Caribbean milkweed
* *Asclepias oenotheroide* – zizotes milkweed
* *Asclepias perennis* – aquatic milkweed
* *Asclepias speciosa* – showy milkweed
* *Asclepias subulata* – rush milkweed
* *Asclepias syriaca* – common milkweed
* *Asclepias tuberosa* – butterfly weed
* *Asclepias variegata* – white milkweed
* *Asclepias verticillata* – whorled milkweed
* *Asclepias vestita* – woolly milkweed
* *Asclepias viridis* – green antelopehorn milkweed
* *Calotropis gigantea* – crown flower
* *Calotropis procera*
* *Cynanchum laeve* – sand vine milkweed
* *Sarcostemma clausa* – white vine

*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. This is thought to adversely affect migration patterns, and to cause a dramatic buildup of the dangerous parasite, *Ophryocystis elektroscirrha*. 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.

## Adult food sources

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

* *Apocynum cannabinum* – Indian hemp
* *Asclepias* sp. – milkweeds
* *Aster* sp. – asters
* *Cirsium* sp. – thistles
* *Daucus carota* – wild carrot
* *Dipsacus sylvestris* – teasel
* *Echinacea* sp. – coneflowers
* *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
* *Syringa vulgaris* – lilac
* *Trifolium pratense* – red clover
* *Vernonia altissima* – tall ironweed

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.

## Migration

In North America, monarchs migrate both north and south on an annual basis, in a long-distance journey that is fraught with risks. 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.

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

## Vision

Physiological experiments suggest that monarch butterflies view the world through a tetrachromatic system. 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.

In addition to these three photoreceptors cells in the main retina, monarch butterfly eyes contain orange filtering pigments that filter the light reaching some but not all green-absorbing opsins, thereby making a fourth photoreceptor cell sensitive to longer wavelength light. The combination of filtered and unfiltered green opsins permits the butterflies to distinguish yellow from orange colors. 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 in order to orient themselves with the sun for their long migratory flight.

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 to lay eggs on. One study found that floral color is more easily recognized at a distance by butterflies searching for nectar than floral shape. This is may be because flowers have highly contrasting colors to the green background of a vegetative landscape. 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. Researchers have found that 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 one's eggs, the roles of color and shape are switched. There may also be a difference between male and female butterflies from other species in terms of the ability to learn certain colors; however, there is no differences between the sexes for monarch butterflies.

## Interactions with predators

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.

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.

Butterfly weed (*A. tuberosa*) lacks significant amounts of cardiac glycosides (cardenolides), but instead contains other types of toxic glycosides, including pregnanes. This difference may reduce the toxicity of monarchs whose larvae feed on that milkweed species, as a naturalist and others have reported that monarch caterpillars do not favor the plant. Some other milkweeds have similar characteristics.

### Types of predators

While monarchs have a wide range of natural predators, none of these are 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 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. The black-headed grosbeak, on the other hand, has developed an insensitivity to secondary plant poisons that allows it to ingest monarchs without vomiting. As a result, orioles and grosbeaks will periodically have high levels of cardenolides in their bodies, and they will be forced to go on periods of reduced monarch consumption. This cycle effectively reduces potential predation of monarchs by 50 percent and indicates that monarch aposematism has a legitimate purpose. Other bird predators include brown thrashers, grackles, robins, cardinals, sparrows, scrub jays, and pinyon jays.

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.

Some mice, particularly the black-eared mouse (*Peromyscus melanotis*) are able to tolerate large doses of cardenolides and are able to eat monarchs. 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 will eat up to 40 monarchs per night.

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*). The Chinese mantis (*Tenodera sinensis*) will consume the larvae once the gut is removed thus avoiding cardenolides. Predatory wasps commonly consume larvae, though large larvae may avoid wasp predation by dropping from the plant or by jerking their bodies.

### Aposematism

Monarchs are toxic and foul-tasting because of the presence of cardenolides in their bodies, which the caterpillars ingest as they feed on milkweed. 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. 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. 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.

Additional studies have shown that different species of milkweed have different effects on growth, virulence, and transmission of parasites. One species, *Asclepias curassavica*, appears to reduce the symptoms of *Ophryocystis elektroscirrha* (OE) infection. There are two possible explanations for this: 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. *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 will only add more OE to the local population.

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. In order to combat predators that remove the wings only to ingest the abdomen, monarchs keep the most potent cardiac glycosides in their abdomens.

### 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 reportedly more unpalatable than the monarch, making this a case of Müllerian mimicry.

## Human interaction

The monarch is the state insect of Alabama, Idaho, Illinois, Minnesota, Texas, Vermont, and West Virginia. Legislation was introduced to make it the national insect of the United States, but this failed in 1989 and again in 1991.

A growing number of homeowners are 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.

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.

Sanctuaries and reserves have been created at overwintering locations in Mexico and California to limit habitat destruction. These sites can generate significant tourism revenue.
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.

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

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

### Captive rearing

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

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.

The frequent media reports of monarch declines has 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.

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. 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.

In addition to the disease risks, researchers believe these captive-reared monarchs are not as fit as wild ones, owing to the unnatural conditions they are raised in. 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 adult monarchs 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.

A study published in 2019 shed light on the fitness of captive-reared monarchs, by testing reared and wild monarchs on a tethered flight apparatus that assessed navigational ability. 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".

An unpublished study in 2019 compared behavior of captive-reared versus wild monarch larvae. 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

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.

### Western monarch populations

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

The Society's annual winter count of 2021 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.

### Eastern and midwestern monarch populations

A 2016 publicaton attributed the previous decade's ten-fold decline in overwintering numbers of the eastern monarch population to the loss of breeding habitat and milkweed. The publication's authors stated that there was an 11%–57% probability that this population will go quasi-extinct over the next 20 years.

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. To help fight this problem, Monarch Watch encourages the planting of "Monarch Waystations".

#### Habitat loss due to herbicide use and genetically modified crops

Declines in milkweed abundance and monarch populatons 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. 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.

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. However, a 2018 study has suggested that the decline in milkweed predates the arrival of GM crops.

#### Losses during migration

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.

The lack of long-term declines in the numbers of breeding and migratory monarchs, yet the clear declines in overwintering numbers, suggests there is a growing disconnect between these life stages. One researcher has suggested that mortality from car strikes constitutes an increasing threat to migrating monarchs. 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.

#### Loss of overwintering habitat

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.

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.

### Parasites

Parasites include the tachinid flies *Sturmia convergens* 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.

Pteromalid wasps, specifically *Pteromalus cassotis*, parasitize Monarch pupae. 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, 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.

The protozoan *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.

Infection with *Ophryocystis 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. Owners of commercial butterfly breeding operations claim that they take steps to control this parasite in their practices, although this claim is doubted by many scientists who study monarchs.

### 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.

### 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 35 °C (95 °F) can be lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate." If a monarch's body temperatures is below 30 °C (86 °F) a monarch cannot fly. To warm up they will sit in the sun or rapidly shiver their wings to warm themselves.

There is concern that climate change will 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. While this will expand the breeding locations of the monarch, this will also have the effect of increasing the distance that monarchs must travel to reach their overwintering destination in Mexico, and this could result in greater mortality during the migration.

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. It is therefore not known whether increased temperatures make milkweed too toxic for monarch caterpillars when other factors are not present. Additionally, milkweed grown at carbon dioxide levels of 760 parts per million (ppm) plants were found to produce a different mix of the toxic cardenolides, one that was less effective against monarch parasites.

## Conservation status

The monarch butterfly is not currently listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) or protected specifically under U.S. domestic laws. On 14 August 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, 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 3 March 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.

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, 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.

In Ontario, Canada, the monarch butterfly is listed as a species of special concern. 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.

In Nova Scotia, the monarch is listed as endangered at the provincial level, as of 2017. It appears that 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. Two recent studies have been conducted examining long-term trends in monarch abundance in Canada, using either butterfly atlas records or citizen science butterfly surveys, and neither shows evidence of a population decline in Canada.

## Conservation efforts

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.

### Federal actions

On 20 June 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.
>
>

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.
>
>

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.

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.

On December 4, 2015, President Obama signed into law the Fixing America’s Surface Transportation (FAST) Act (Pub. L. 114-94). 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.
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.

The United States Department of Agriculture'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 U.S. Fish and Wildlife Service has designated to be threatened or endangered.

### Other actions

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.

#### National Cooperative Highway Research Program report

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.

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. There is also evidence that monarch larvae living near roads experience physiological stress conditions, as evidenced by elevations in their heart rate.

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. 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.
>
>

### Butterfly gardening

While there are few scientific studies on the subject, the practice of butterfly gardening and creating "monarch waystations" is commonly thought to increase the populations of butterflies. 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.

For example, in the Washington, D.C. area and elsewhere in the northeastern United States, monarchs prefer to reproduce on common milkweed (*A. syriaca*), especially when its foliage is soft and fresh. Because monarch reproduction in that area peaks in 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. In addition, the seeds of *A. syriaca* and some other milkweeds need periods of cold treatment (cold stratification) before they will germinate.

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 in (13 mm) layer of straw mulch. 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.

Although monarch caterpillars will feed on butterfly weed (*A. tuberosa*) in butterfly gardens, the plant has rough leaves and is typically not a heavily used host plant for monarch caterpillars. The plant's low levels of cardenolides may also make the plant unattractive to egg-laying monarchs. 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.

Breeding monarchs prefer to lay eggs on swamp milkweed (*A. incarnata*). 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. 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.

## See also

* Butterflies
* Butterfly house (conservatory)
* Lepidoptera
* Lepidoptera migration
* Monarch Butterfly Biosphere Reserve
* Peninsula Point Light, Michigan

## References

1. ↑ Monarch, NatureServe Explorer
2. ↑ Committee On Generic Nomenclature, Royal Entomological Society of London (2007) [1934]. *The Generic Names of British Insects*. Royal Entomological Society of London Committee on Generic Nomenclature, Committee on Generic Nomenclature. British Museum (Natural History). Dept. of Entomology. p. 20.
3. ↑ Scudder, Samuel H.; William M. Davis; Charles W. Woodworth; Leland O. Howard; Charles V. Riley; Samuel W. Williston (1989). *The butterflies of the eastern United States and Canada with special reference to New England*. The author. p. 721. ISBN 978-0-665-26322-4.
4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Agrawal, Anurag (7 March 2017). *Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution*. Princeton University Press. ISBN 9781400884766.
5. ↑ 5.0 5.1 Savela, Markku (25 February 2019). "*Danaus plexippus* (Linnaeus, 1758)". *Lepidoptera and Some Other Life Forms*. Retrieved 11 July 2020.
6. ↑ "Conserving Monarch Butterflies and their Habitats". USDA. 2015.
7. ↑ 7.0 7.1 Garber, Steven D. (1998). *The Urban Naturalist*. Courier Dover Publications. pp. 76–79. ISBN 978-0-486-40399-1.
8. ↑ Groth, Jacob (10 November 2000). "Monarch Migration Study". Swallowtail Farms. Retrieved 21 July 2014.
9. ↑ "Monarch Migration". Monarch Joint Venture. 2013.
10. ↑ 10.00 10.01 10.02 10.03 10.04 10.05 10.06 10.07 10.08 10.09 10.10 10.11 10.12 "Petition to protect the Monarch butterfly (*Danaus plexippus plexippus*) under the endangered species act" (PDF). Xerces Society. Retrieved 1 September 2014.
11. ↑ "Butterflies Emerge from Cocoons Aboard Station". NASA. 2009.
12. ↑ Adams, Jean Ruth (1992). *Insect Potpourri: Adventures in Entomology*. CRC Press. pp. 28–29. ISBN 978-1-877743-09-2.
13. ↑ Linnaeus, Carl (1758). *Systema Naturae* (in Latin). **1**. Stockholm: Laurentius Salvius. p. 471. OCLC 174638949. Retrieved 5 June 2012.
14. ↑ πλήξιππος. Liddell, Henry George; Scott, Robert; *A Greek–English Lexicon* at the Perseus Project
15. ↑ Linnaeus, C. (1758). *Systema Naturae* ed. X: 467 (in BHL)
16. ↑ Pyle, Robert Michael (2001). *Chasing Monarchs: Migrating with the Butterflies of Passage*. Houghton Mifflin Books. pp. 148–149. ISBN 978-0-618-12743-6.
17. ↑ 17.0 17.1 Smith, David A.; Gugs Lushai and John A. Allen (2005). "A classification of *Danaus* butterflies (Lepidoptera: Nymphalidae) based upon data from morphology and DNA". *Zoological Journal of the Linnean Society*. **144** (2): 191–212. doi:10.1111/j.1096-3642.2005.00169.x .
"IUCN Red List of Threatened Species, Version 2014.1". *IUCN Red List of Threatened Species*. Retrieved 13 July 2014. old-form url
Gibbs, Lawrence; Taylor, O. R. (1998). "The White Monarch". Department of Entomology University of Kansas. Retrieved 17 July 2014.
Groth, Jacob (10 November 2000). "Monarch Migration Study". Swallowtail Farms. Retrieved 22 July 2014.
21. ↑ 21.0 21.1 Hay-Roe, Miriam M.; Lamas, Gerardo; Nation, James L. (2007). "Pre- and postzygotic isolation and Haldane rule effects in reciprocal crosses of *Danaus erippus* and *Danaus plexippus* (Lepidoptera: Danainae), supported by differentiation of cuticular hydrocarbons, establish their status as separate species". *Biological Journal of the Linnean Society*. **91** (3): 445–453. doi:10.1111/j.1095-8312.2007.00809.x .
22. ↑ Ackery, P. R.; Vaine-Wright, R. I. (1984). *Milkweed butterflies, their cladistics and biology: being an account of the natural history of the Danainae, subfamily of the Lepidoptera, Nymphalidae*. British Museum (Natural History), London. p. 17. ISBN 978-0-565-00893-2.
23. ↑ Zhan, Shuai; Merlin, Christine; Boore, Jeffrey L.; Reppert, Steven M. (November 2011). "The Monarch Butterfly Genome Yields Insights into Long-Distance Migration". *Cell*. **147** (5): 1171–85. doi:10.1016/j.cell.2011.09.052. PMC 3225893 . PMID 22118469.
24. ↑ Stensmyr, Marcus C.; Hansson, Bill S. (November 2011). "A Genome Befitting a Monarch". *Cell*. **147** (5): 970–2. doi:10.1016/j.cell.2011.11.009 . PMID 22118454.
25. ↑ Johnson, Carolyn Y. (23 November 2011). "Monarch butterfly genome sequenced". *Boston Globe* (Boston, MA). https://www.boston.com/Boston/whitecoatnotes/2011/11/monarch-butterfly-genome-sequenced/gF1mFBxXCLUOHigi2FOHPM/index.html.
26. ↑ Zhan, Shuia; Zhang, Wei; Niitepold, Kristjan; Hsu, Jeremy; Haeger, Juan Fernandez; Zalucki, Myron P.; Altizer, Sonia; de Roode, Jacobus C.; Reppert, Stephen M.; Kronforst, Marcus R. (1 October 2014). "The genetics of Monarch butterfly migration and warning coloration". *Nature*. **514** (7522): 317–321. Bibcode:2014Natur.514..317Z. doi:10.1038/nature13812. PMC 4331202 . PMID 25274300.
27. ↑ 27.0 27.1 Zhan, Shuai; Merlin, Christine; Boore, Jeffrey L.; Reppert, Steven M. (23 November 2012). "The monarch butterfly genome yields insights into long-distance migration". *Cell*. **147** (5): 1171–1185. doi:10.1016/j.cell.2011.09.052. PMC 3225893 . PMID 22118469.
28. ↑ Gasmi, Laila; Boulain, Helene; Gauthier, Jeremy; Hua-Van, Aurelie; Musset, Karine; Jakubowska, Agata K.; Aury, Jean-Marc; Volkoff, Anne-Nathalie; Huguet, Elisabeth (17 September 2015). "Recurrent Domestication by Lepidoptera of Genes from Their Parasites Mediated by Bracoviruses". *PLOS Genet*. **11** (9): e1005470. doi:10.1371/journal.pgen.1005470. PMC 4574769 . PMID 26379286.
29. ↑ Le Page, Michael (17 September 2015). "If viruses transfer wasp genes into butterflies, are they GM?". The New Scientist. Retrieved 13 July 2016.
30. ↑ Main, Douglas (17 September 2015). "Wasps Have Genetically Modified Butterflies, Using Viruses". Newsweek. Retrieved 13 July 2016.
31. ↑ 31.0 31.1 Oberhauser (2004), p. 3
32. ↑ "Monarch Butterfly Life Cycle and Migration". *National Geographic Education*. 24 October 2008. Retrieved 15 August 2013.
33. ↑ "Egg". Monarch Joint Venture. 2021. Archived from the original on July 11, 2021. Retrieved October 6, 2021.
34. ↑ Oberhauser (2004), p. 23
35. ↑ Lefevre, T.; Chiang, A.; Li, H; Li, J; de Castillejo, C.L.; Oliver, L.; Potini, Y.; Hunter, M. D.; de Roode, J.C. (2012). "Behavioral resistance against a protozoan parasite in the monarch butterfly" (PDF). *Journal of Animal Ecology*. **81** (1): 70–9. doi:10.1111/j.1365-2656.2011.01901.x . hdl:2027.42/89483. PMID 21939438.
"The other butterfly effect – A youth reporter talks to Jaap de Roode". TED Blog. 25 November 2014. Retrieved 12 December 2014.
37. ↑ Oberhauser (2004), p. 51
38. ↑ 38.0 38.1 38.2 38.3 38.4 38.5 38.6 "Guide to Monarch Instars". Monarch Joint Venture. 2021. Archived from the original on August 1, 2021. Retrieved October 1, 2021.
39. ↑ Collie, Joseph; Granela, Odelvys; Brown, Elizabeth B.; Keene, Alex C. (November 2020). "Aggression Is Induced by Resource Limitation in the Monarch Caterpillar". *iScience*. **23** (12): 101791. Bibcode:2020iSci...23j1791C. doi:10.1016/j.isci.2020.101791 . PMC 7756136  Check `|pmc=` value (help). PMID 33376972 Check `|pmid=` value (help).
40. ↑ Petersen, B. (1964). "Humidity, Darkness, and Gold Spots as Possible Factors in Pupal Duration of Monarch Butterflies". *J. Lepidopterists' Soc*. **18**: 230–232.
41. ↑ (1)"Pupa". Monarch Joint Venture. 2021. Archived from the original on July 11, 2021. Retrieved October 5, 2021.
(2) Pocius, V M; Debinski, D M; Pleasants, J M; Bidne, K G; Hellmich, R L; Brower, L P (2017-09-07). "Milkweed Matters: Monarch Butterfly (Lepidoptera: Nymphalidae) Survival and Development on Nine Midwestern Milkweed Species". *Environmental Entomology*. **46** (5): 1098–1105. doi:10.1093/ee/nvx137 . ISSN 0046-225X. PMC 5850784 . PMID 28961914.
42. ↑ "Reproduction". *Monarch Lab*. Regents of the University of Minnesota. Archived from the original on July 16, 2019. Retrieved 13 December 2014.
43. ↑ 43.0 43.1 Braby, Michael F. (2000). *Butterflies of Australia: Their Identification, Biology and Distribution*. CSIRO Publishing. pp. 597–599. ISBN 978-0-643-06591-8.
44. ↑ Satterfield, Dara A.; Davis, Andrew K. (April 2014). "Variation in wing characteristics of monarch butterflies during migration: Earlier migrants have redder and more elongated wings". *Animal Migration*. **2** (1). doi:10.2478/ami-2014-0001 .
45. ↑ Davis, A. K.; Holden, Michael T. (2015). "Measuring Intraspecific Variation in Flight-Related Morphology of Monarch Butterflies (Danaus plexippus): Which Sex Has the Best Flying Gear?" (PDF). *Journal of Insects*. Hindawi Publishing Corporation. **2015** (59170): 1–6. doi:10.1155/2015/591705 . Retrieved October 17, 2020.
46. ↑ "Monarch, *Danaus plexippus*". Archived from the original on 15 December 2012. Retrieved 27 August 2008.
47. ↑ (1) "Adult". Monarch Joint Venture. 2021. Archived from the original on July 21, 2021. Retrieved October 5, 2021.
(2) "Sensory Systems". *Biology*. Monarch Watch. Archived from the original on March 19, 2018. Retrieved October 5, 2021.
(3) "Sexing Monarchs". *Biology*. Monarch Watch. Archived from the original on May 5, 2021. Retrieved October 5, 2021. }
48. ↑ Darby, Gene (1958). *What is a Butterfly*. Chicago: Benefic Press. p. 10.
49. ↑ Flockhart, D. T. Tyler; Martin, Tara G.; Norris, D. Ryan (2012). "Experimental Examination of Intraspecific Density-Dependent Competition during the Breeding in Monarch Butterflies (*Danaus plexippus*)". *PLOS ONE*. **7** (9): e45080. Bibcode:2012PLoSO...745080F. doi:10.1371/journal.pone.0045080 . PMC 3440312 . PMID 22984614.
50. ↑ Klots, Alexander B. (1951). *A Field Guide to the Butterflies of North America, East of the Great Plains* (Tenth ed.). Boston: Houghton Mifflin Company. pp. 78, 79. ISBN 978-0395078655.
51. ↑ "monarchscience". Akdavis6.wixsite.com. 31 December 2016. Retrieved 6 January 2017.
52. ↑ Emmel, Thomas C. (1997). *Florida's Fabulous Butterflies.* p. 44, World Publications, ISBN 0-911977-15-5
53. ↑ Oberhauser (2004), pp. 61–68.
54. ↑ Frey, D.; Leong, K. L. H.; Peffer, E.; Smidt, R. K.; Oberhauser, K. S. (1998). "Mating patterns of overwintering monarch butterflies (*Danaus plexippus* (L.)) in California" (PDF). *J. Lepid. Soc*. **52**: 84–97.
55. ↑ Solensky, M.J.; K.S. Oberhauser (2009). "Sperm Precedence in Monarch Butterflies (*Danaus plexippus*)". *Behavioral Ecology*. **20** (2): 328–34. doi:10.1093/beheco/arp003 .
56. ↑ Oberhauser, K. S. (1989). "Effects of spermatophores on male and female monarch butterfly reproductive success". *Behavioral Ecology and Sociobiology*. **25** (4): 237–246. doi:10.1007/bf00300049.
57. ↑ 57.0 57.1 "ADW: *Danaus plexippus*: Information". Retrieved 27 August 2008.
58. ↑ Solensky, Michelle J. (November 2004). "The Effect of Behavior and Ecology on Male Mating Success in Overwintering Monarch Butterflies (*Danaus plexippus*)". *Journal of Insect Behavior*. **17** (6): 723–743. doi:10.1023/b:joir.0000048985.58159.0d. ISSN 0892-7553.
59. ↑ Gerald McCormack (7 December 2005). "Cook Islands' Largest Butterfly – the Monarch". Cook Islands Biodiversity.
60. ↑ 60.0 60.1 Scott, James A. (1986). *The Butterflies of North America.* Stanford University Press, Stanford, CA. ISBN 0-8047-2013-4
61. ↑ Brower, Lincoln P.; Malcolm, Stephen B. (1991). "Animal Migrations: Endangered Phenomena". *Am. Zool*. **31** (1): 265–276. doi:10.1093/icb/31.1.265 .
62. ↑ Davis, Donald (27 November 2014). "DPLEX-L:59250 THE possibility of a trans-Gulf migration, oil rigs, Dr. Gary Ross, and more". *Monarch Watch*. University of Kansas.
63. ↑ "Monarch Sightings Map". Monarch Butterfly New Zealand Trust. Archived from the original on 12 February 2021. Retrieved 15 December 2014.
64. ↑ "The lonely flight of the monarch butterfly". NewsAdvance.com, Lynchburg, Virginia Area. Retrieved 7 October 2014.
65. ↑ "Provisional species list of the Lepidoptera". Gibraltar Ornithological and Natural History Society. Archived from the original on 25 September 2015.
66. ↑ Pais, Miguel. "Northwestern African sightings of *D. plexippus*, Maroc>Pappilons>*Danaus plexippus*". Google Maps. Retrieved 19 September 2014.
67. ↑ Coombes, Simon. "1995 Monarch Invasion of the UK". butterfly-guide.co.uk.
68. ↑ 68.0 68.1 Cech, Rick and Tudor, Guy (2005). *Butterflies of the East Coast*. Princeton University Press, Princeton, NJ. ISBN 0-691-09055-6
69. ↑ 69.0 69.1 69.2 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. ISBN 0-86727-107-8
70. ↑ "Monarch Butterfly Journey North". Annenberg Learner. Archived from the original on 14 October 2017. Retrieved 16 July 2017.
71. ↑ Pyle, Robert Michael (2014). *Chasing monarchs: Migrating with the butterflies of passage*. Yale University Press. p. 2. ISBN 978-0395828205.
72. ↑ Halpern, Sue (2002). *Four Wings and a Prayer*. Kindle edition location 1594. New York, New York: Random House. ISBN 978-0-307-78720-0.
73. ↑ 73.00 73.01 73.02 73.03 73.04 73.05 73.06 73.07 73.08 73.09 73.10 73.11 73.12 73.13 73.14 73.15 73.16 73.17 73.18 "Plant Milkweed for Monarchs" (PDF). *Monarch Joint Venture Partnering across the U.S. to conserve the monarch migration*. Monarch Joint Venture. Archived from the original (PDF) on 21 May 2015. Retrieved 7 July 2015.
74. ↑ (1) USDA, NRCS (n.d.). "*Asclepias incarnata*". *The PLANTS Database (plants.usda.gov)*. Greensboro, North Carolina: National Plant Data Team.
(2) Kirk, S.; Belt, S. "Plant fact sheet for swamp milkweed (Asclepias incarnata)" (PDF). Beltsville, Maryland: United States Department of Agriculture: Natural Resources Conservation Service: Norman A. Berg National Plant Materials Center. Archived from the original (PDF) on July 9, 2021. Retrieved July 9, 2021.
(3) Holmes, Forest Russell. "Swamp Milkweed (Asclepias incarnata L.)". *Plant of the Week*. Washington, D.C.: United States Department of Agriculture: United States Forest Service. Archived from the original on March 28, 2021. Retrieved July 9, 2021.
(4) "Northeast Region Milkweed Species: Swamp Milkweed: Asclepias incarnata" (PDF). *Plant Milkweed for Monarchs*. Monarch Joint Venture. Archived from the original (PDF) on 21 May 2015. Retrieved 7 July 2015.
75. ↑ "*Asclepias nivea*". *Butterfly gardening & all things milkweed*. Archived from the original on 7 July 2015. Retrieved 7 July 2015.
76. ↑ Stevens, Michelle (May 30, 2006). "Plant guide for *Asclepias speciosa*" (PDF). United States Department of Agriculture: Natural Resources Conservation Service. Archived from the original (PDF) on July 12, 2021. Retrieved July 12, 2021.
(2) Young-Mathews, A.; Eldredge, E. (2012). "Plant fact sheet for showy milkweed (Asclepias speciosa)" (PDF). United States Department of Agriculture: Natural Resources Conservation Service, Corvallis Plant Materials Center, Oregon, and Great Basin Plant Materials Center, Fallon, Nevada. Archived from the original (PDF) on April 1, 2021. Retrieved July 12, 2021.
(3) "Asclepias speciosa". Washington, D.C.: United States Department of Agriculture: United States Forest Service. Archived from the original on March 7, 2021. Retrieved July 12, 2021.
(4) Wiese, Karen (2000). "Showy Milkweed: *Asclepias speciosa*". *Sierra Nevada wildflowers: a field guide to common wildflowers and shrubs of the Sierra Nevada, including Yosemite, Sequoia, and Kings Canyon National Parks*. Helena, Montana: Falcon Publishing, Inc. p. 50. ISBN 0585362831. LCCN 00022385. OCLC 47011272. Retrieved July 12, 2021 – via Internet Archive.
77. ↑ (1) Stevens, Michelle. "Plant guide for common milkweed (Asclepias syriaca)" (PDF). Washington, D.C.: United States Department of Agriculture: Natural Resources Conservation Service: National Plant Data Center. Archived from the original (PDF) on July 5, 2021. Retrieved July 5, 2021.
(2) Taylor, David. "Common Milkweed (Asclepias syriaca L.)". *Plant of the Week*. United States Department of Agriculture: United States Forest Service. Archived from the original on June 4, 2021. Retrieved July 9, 2021.
(3) Higgins, Adrian (27 May 2015). "A gardener's guide to saving the monarch". *Home & Garden* (The Washington Post). http://www.washingtonpost.com/lifestyle/home/creating-a-rest-stop-for-the-monarch/2015/05/26/cd81a75c-ffcb-11e4-805c-c3f407e5a9e9\_story.html.
(4) Higgins, Adrian (27 May 2015). "7 milkweed varieties and where to find them". *Home & Garden* (The Washington Post). https://www.washingtonpost.com/lifestyle/home/a-world-of-milkweeds/2015/05/26/43fba7d6-fe6c-11e4-833c-a2de05b6b2a4\_story.html.
(5) Gomez, Tony. "*Asclepias syriaca*: Common Milkweed for Monarch Caterpillars". *Monarch Butterfly Garden*. MonarchButterflyGarden.net. Archived from the original on 16 March 2015. Retrieved 5 July 2021.
(6) "*Asclepias syriaca*". *Butterfly gardening & all things milkweed*. Archived from the original on 7 July 2015. Retrieved 7 July 2015.
(7) "Northeast Region Milkweed Species: Common Milkweed: Asclepias syriaca" (PDF). *Plant Milkweed for Monarchs*. Monarch Joint Venture. Archived from the original (PDF) on 21 May 2015. Retrieved 7 July 2015.
78. ↑ (1) Davis, Lee (May 31, 2006). "Plant guide for Green Milkweed: *Asclepias viridis* Walt." (PDF). Washington, D.C.: United States Department of Agriculture: Natural Resources Conservation Service. Archived from the original (PDF) on July 11, 2021. Retrieved July 11, 2021.
(2) Taylor, David. "Green Antelopehorn (*Asclepias viridis*)". *Plant of the Week*. Washington, D.C.: United States Department of Agriculture: United States Forest Service. Archived from the original on March 27, 2021. Retrieved July 11, 2021.
(3) Borders, Brianna, The Xerces Society; Casey, Allen, USDA-NRCS Missouri; Row, John M., USDA-NRCS Kansas; Wynia, Rich, USDA-NRCS Kansas; King, Randy, USDA-NRCS Arkansas; Jacobs, Alayna, USDA-NRCS Arkansas; Taylor, Chip, Monarch Watch; Mader, Eric, The Xerces Society (June 24, 2013). Walls, Hailey, The Xerces Society; Rich, Kaitlyn, The Xerces Society, eds. "*Asclepias viridis* Green antelopehorn" (PDF). *Pollinator Plants of the Central United States: Native Milkweeds (Asclepias spp.)*. Washington, D.C.: United States Department of Agriculture: Natural Resources Conservation Service. Archived from the original (PDF) on March 31, 2021. Retrieved July 11, 2021.
(4) "Asclepias viridis: Spider Milkweed". *NatureServe*. Archived from the original on September 19, 2021. Retrieved July 11, 2021.
79. ↑ "Butterfly Society of Hawaii". Butterfly Society of Hawaii. Retrieved 6 January 2017.
80. ↑ Butterfly Gardening. kansasnativeplants.com
81. ↑ Wagner, David L. (2005). *Caterpillars of Eastern North America*. Princeton University Press, Princeton, NJ. ISBN 0-691-12144-3
82. ↑ Howard, Elizabeth; Aschen, Harlen; Davis, Andrew K. (2010). "Citizen Science Observations of Monarch Butterfly Overwintering in the Southern United States". *Psyche: A Journal of Entomology*. **2010**: 1. doi:10.1155/2010/689301 .
83. ↑ Satterfield, D. A.; Maerz, J. C.; Altizer, S (2015). "Loss of migratory behaviour increases infection risk for a butterfly host". *Proceedings of the Royal Society B: Biological Sciences*. **282** (1801): 20141734. doi:10.1098/rspb.2014.1734. PMC 4308991 . PMID 25589600.
84. ↑ Majewska, Ania A.; Altizer, Sonia (16 August 2019). "Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies". *Insects*. **10** (8): 253. doi:10.3390/insects10080253 . PMC 6724006  Check `|pmc=` value (help). PMID 31426310.
85. ↑ "Nectar Plants for Butterflies & Other Pollinators" (PDF). *Plants for Butterfly and Pollinator Gardens: Native and Non-native Plants Suitable for Gardens in the Northeastern United States*. Monarch Watch. Archived from the original (PDF) on October 1, 2021. Retrieved October 1, 2021.
86. ↑ "North American Monarch Conservation Plan" (PDF). Commission for Environmental Cooperation. Retrieved 17 October 2014.
87. ↑ Taylor, O. R. (3 August 2000). "Monarch Watch 1999 Season Recoveries" (PDF). pp. 1–11. Archived from the original (PDF) on 6 January 2014. Retrieved 5 July 2021.
88. ↑ 88.0 88.1 Steffy, Gayle (2015). "Trends observed in fall migrant Monarch butterflies (Lepidoptera: Nymphalidae) east of the Appalachian Mountains at an inland stopover in southern Pennsylvania over an eighteen year period". *Annals of the Entomological Society of America*. **108** (5): 718. doi:10.1093/aesa/sav046.
"Monarch butterflies are a steady presence in Arizona". *Arizona Daily Star*. http://tucson.com/news/local/monarch-butterflies-are-a-steady-presence-in-arizona/article\_efe1d0f4-78de-51a7-a173-00b3545be057.html.
90. ↑ "Butterfly genomics: Monarchs migrate and fly differently, but meet up and mate". *phys.org*. Retrieved 2020-07-31.
91. ↑ 91.0 91.1 91.2 Blackiston, Douglas; Briscoe, Adriana D.; Weiss, Martha R. (1 February 2011). "Color vision and learning in the monarch butterfly, *Danaus plexippus* (Nymphalidae)". *The Journal of Experimental Biology*. **214** (Pt 3): 509–520. doi:10.1242/jeb.048728 . ISSN 1477-9145. PMID 21228210.
92. ↑ Stalleicken, Julia; Labhart, Thomas; Mouritsen, Henrik (March 2006). "Physiological characterization of the compound eye in monarch butterflies with focus on the dorsal rim area". *Journal of Comparative Physiology A*. **192** (3): 321–331. doi:10.1007/s00359-005-0073-6. ISSN 0340-7594. PMID 16317560.
93. ↑ Sauman, Ivo; Briscoe, Adriana D.; Zhu, Haisun; Shi, Dingding; Froy, Oren; Stalleicken, Julia; Yuan, Quan; Casselman, Amy; Reppert, Steven M. (5 May 2005). "Connecting the Navigational Clock to Sun Compass Input in Monarch Butterfly Brain". *Neuron*. **46** (3): 457–467. doi:10.1016/j.neuron.2005.03.014 . ISSN 0896-6273. PMID 15882645.
94. ↑ 94.0 94.1 Cepero, Laurel C.; Rosenwald, Laura C.; Weiss, Martha R. (1 July 2015). "The Relative Importance of Flower Color and Shape for the Foraging Monarch Butterfly (Lepidoptera: Nymphalidae)". *Journal of Insect Behavior*. **28** (4): 499–511. doi:10.1007/s10905-015-9519-z. ISSN 1572-8889.
95. ↑ "monarchscience". Akdavis6.wixsite.com. 5 April 2016.
96. ↑ 96.0 96.1 Barbosa, Pedro; Deborah Kay Letourneau (1988). "5". *Novel Aspects of Insect-plant Interactions*. Wiley-Interscience. pp. 29–31. ISBN 978-0-471-83276-8.
97. ↑ (1) "Butterfly Weed: *Asclepias tuberosa*" (PDF). Becker County, Minnesota: Becker Soil and Water Conservation District. Archived from the original (PDF) 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).
(2) Mikkelsen, Lauge Hjorth; Hamoudi, Hassan; Altuntas Gül, 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*.
(3) 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.
98. ↑ 98.0 98.1 (1) 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.
(2) Abugattas, Alonzo (3 January 2017). "Monarch Way Stations". *Capital Naturalist*. Archived from the original on 5 June 2017. Retrieved 5 June 2017 – via Blogger. (*A. tuberosa*) is the least favored by monarch caterpillars .... because it has very little toxin (cardiac glycosides) in its leaves, .... .
(3) Gomez, Tony. "*Asclepias tuberosa*: Butterfly Weed for Monarchs and More". *Monarch Butterfly Garden*. MonarchButterflyGarden.net. Archived from the original on 16 August 2017. Retrieved 17 October 2010. Rough leaves for monarch caterpillars, not typically a heavily used host plant
(4) 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 (ESA). **9** (1): 1–13. doi:10.1002/ecs2.2064. Retrieved July 6, 2021 – via Wiley Online Library. 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)
99. ↑ 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 (ESA). **9** (1): 1–13. doi:10.1002/ecs2.2064. Retrieved July 6, 2021 – via Wiley Online Library. 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)
100. ↑ 100.0 100.1 Brower, Lincoln (1988). "Avian Predation on the Monarch Butterfly and Its Implications for Mimicry Theory". *The American Naturalist*. **131**: S4–S6. doi:10.1086/284763.
101. ↑ Stimson, John; Mark Berman (1990). "Predator induced colour polymorphism in *Danaus plexippus* L. (Lepidoptera: Nymphalidae) in Hawaii". *Heredity*. **65** (3): 401–406. doi:10.1038/hdy.1990.110 . Lay summary.  Cite uses deprecated parameter `|lay-url=` (help)
102. ↑ 102.0 102.1 Álvarez-Castañeda, Sergio Ticul (2005). "Peromyscus melanotis". *Mammalian Species*. **2005** (764): 1–4. doi:10.1644/1545-1410(2005)764[0001:PM]2.0.CO;2.
103. ↑ Koch, R. L.; W. D. Hutchison; R. C. Venette; G. E. Heimpel (October 2003). "Susceptibility of immature monarch butterfly, *Danaus plexippus* (Lepidoptera: Nymphalidae: Danainae), to predation by *Harmonia axyridis* (Coleoptera: Coccinellidae)". *Biological Control*. **28** (2): 265–270. doi:10.1016/S1049-9644(03)00102-6.
104. ↑ Rafter, Jamie; Anurag Agruwal; Evan Preisser (2013). "Chinese mantids gut caterpillars: avoidance of prey defense?". *Ecological Entomology*. **38** (1): 78–82. doi:10.1111/j.1365-2311.2012.01408.x.
105. ↑ Zalucki, Myron P.; Malcolm, Stephen B.; Paine, Timothy D.; Hanlon, Christopher C.; Brower, Lincoln P.; Clarke, Anthony R. (2001). "It's the first bites that count: Survival of first-instar monarchs on milkweeds". *Austral Ecology*. **26** (5): 547–555. doi:10.1046/j.1442-9993.2001.01132.x.
106. ↑ Oberhauser (2004), p. 44
107. ↑ Karageorgi, Marianthi; Groen, Simon C.; Sumbul, Fidan; Pelaez, Julianne N.; Verster, Kirsten I.; Aguilar, Jessica M.; Hastings, Amy P.; Bernstein, Susan L.; Matsunaga, Teruyuki; Astourian, Michael; Guerra, Geno (October 2019). "Genome editing retraces the evolution of toxin resistance in the monarch butterfly". *Nature*. **574** (7778): 409–412. doi:10.1038/s41586-019-1610-8. ISSN 1476-4687. PMC 7039281  Check `|pmc=` value (help). PMID 31578524.
108. ↑ 108.0 108.1 Parsons, J.A. (1965). "A Digitallis-like Toxin in the Monarch Butterfly *Danaus plexippus* L". *The Journal of Physiology*. **178** (2): 290–304. doi:10.1113/jphysiol.1965.sp007628. PMC 1357291 . PMID 14298120.
109. ↑ Malcolm, S. B.; L. P. Brower (1989). "Evolutionary and ecological implications of cardenolide sequestration in the monarch butterfly". *Experientia*. **45** (3): 284–295. doi:10.1007/BF01951814.
110. ↑ 110.0 110.1 de Rood, J. C.; De Castillejo, C. L.; Faits, T.; Alizon, S. (2011). "Virulence evolution in response to anti-infection 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.
111. ↑ "Is tropical milkweed really medicinal? (answer: yes, and that's really really bad for your garden)". *monarchscience*. 16 March 2017. Retrieved 12 December 2019.
112. ↑ 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.
113. ↑ 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. Viceroys are as unpalatable as monarchs, and significantly more unpalatable than queens from representative Florida populations.
114. ↑ "Official Alabama Insect". *Alabama Emblems, Symbols and Honors*. Alabama Department of Archives & History. 12 July 2001. Retrieved 19 March 2007.
115. ↑ "Idaho Symbols, Insect: Monarch Butterfly". *Idaho State Symbols, Emblems, and Mascots*. SHG resources, state handbook & guide. Retrieved 26 March 2008.
116. ↑ "State Symbol: Illinois Official Insect — Monarch Butterfly (*Danaus plexippus*)". *[Illinois] State Symbols*. Illinois State Museum. Retrieved 26 March 2008.
117. ↑ "Minnesota State Symbols" (PDF). Minnesota House of Representatives. Retrieved 26 March 2008.
118. ↑ "Texas State Symbols". The Texas State Library and Archives. Retrieved 26 March 2008.
119. ↑ "(Vermont) State Butterfly". Vermont Department of Libraries. Archived from the original on 18 May 2008. Retrieved 26 March 2008.
120. ↑ "West Virginia Statistical Information, General State Information" (PDF). Official West Virginia Web Portal. Archived from the original (PDF) on 11 April 2008. Retrieved 26 March 2008.
121. ↑ Wade, Nicholas (1 June 1990). "Choosing a National Bug". *The New York Times*. https://www.nytimes.com/1990/06/01/opinion/the-editorial-notebook-choosing-a-national-bug.html.
122. ↑ "Designating the monarch butterfly as the national insect. (1989 - H.J.Res. 411)". *GovTrack.us*.
123. ↑ "Designating the monarch butterfly as the national insect. (1991 - H.J.Res. 200)". *GovTrack.us*.
124. ↑ "Monarch Watch: Monarch Waystation Program". *University of Kansas, Entomology Department*. Archived from the original on 18 November 2019. Retrieved 26 February 2019.
125. ↑ "Flight of the Butterflies". *Reuben H. Fleet Science Center*. Archived from the original on 17 February 2013. Retrieved 18 February 2013.
126. ↑ "Saving Butterflies: Insect Ecologist Spearheads Creation of Oases for Endangered Butterflies". ScienceDaily. 1 January 2005. Archived from the original on 4 June 2008. Retrieved 27 May 2008.
127. ↑ Nicoletti, Mélanie; Gilles, Florent; Galicia-Mendoza, Ivette; Rendón-Salinas, Eduardo; Alonso, Alfonso; Contreras-Garduño, Jorge (2020). "Physiological Costs in Monarch Butterflies Due to Forest Cover and Visitors". *Ecological Indicators*. **117**: 106592. doi:10.1016/j.ecolind.2020.106592 .
128. ↑ "Monarch Monitoring Project". Cap May Bird Observatory. 2008. Archived from the original on 20 December 2008. Retrieved 5 December 2008.
129. ↑ HarperCollins Inc; UK, Faber and Faber
130. ↑ (1)
"Live butterfly release for funerals and butterfly weddings". Fragrant Acres Butterfly Farm. Retrieved 14 November 2014.
131. ↑ "In Memory of 9/11 "Wings of Hope"". gayandciha.com. 4 September 2014. Retrieved 14 November 2014.
(2) Johnson, Pam (24 August 2010). "Join Branford Rotary's 9/11 Town Green Event/Butterfly Release". The Day. Shure Publishing. http://www.theday.com/article/20110824/NWS01/308259715.
132. ↑ "Ormond Beach Flying US Flags On Granada Bridge T0 Mark 9\17". WNDB Local News First. NewsDaytonaBeach.com. 2013. http://newsdaytonabeach.com/ormond-beach-placing-u-s-flags-on-granada-bridge-to-mark-911-anniversary/.
133. ↑ "Monarch Butterfly release at Children's Museum of Fond du Lac". FDL Reporter. Retrieved 14 November 2014.
134. ↑ 134.0 134.1 "Monarch Watch". *University of Kansas, Entomology Department*. Archived from the original on 20 July 2012. Retrieved 20 February 2014.
135. ↑ (1) John Platt TakePart (14 October 2015). "When Butterflies Shouldn't Fly Free". *The Huffington Post*. Retrieved 12 January 2017.
(2) "Are We Loving Monarchs to Death? – The Crux". Blogs.discovermagazine.com. 21 June 2016. Archived from the original on 14 April 2020. Retrieved 12 January 2017.
136. ↑ Love, Orlan (25 August 2016). "Monarch Moonshot: Officials hope to make Linn County center of butterfly production and habitat". The Gazette. Retrieved 12 January 2017.
137. ↑ Rearing Monarchs Responsibly: A conservationist's guide to raising monarchs for science and education. Monarch Joint Venture, University of Minnesota
138. ↑ "monarchscience". Akdavis6.wixsite.com. 7 September 2015.
139. ↑ Tenger-Trolander, Ayşe; Lu, Wei; Noyes, Michelle; Kronforst, Marcus R. (16 July 2019). "Contemporary loss of migration in monarch butterflies". *Proceedings of the National Academy of Sciences*. **116** (29): 14671–14676. doi:10.1073/pnas.1904690116 . ISSN 0027-8424. PMC 6642386  Check `|pmc=` value (help). PMID 31235586.
140. ↑ Maeckle |, Monika (2 July 2019). "Study of "genetic franken monarchs" provokes online ire and debate". *texasbutterflyranch*. Retrieved 12 December 2019.
141. ↑ "Effects of captive-rearing on caterpillar anti-predator behavior - an inside look at some preliminary data". *monarchscience*. 10 August 2019. Retrieved 12 December 2019.
142. ↑ Fears, Darryl (26 August 2015). "As pesticides wipe out Monarch butterflies in the U.S., illegal logging is doing the same in Mexico". *The Washington Post*.
143. ↑ "The Monarch butterfly population in California has plummeted 86% in one year".
144. ↑ "Monarch butterfly population moves closer to extinction". *phys.org*. Retrieved 2021-01-21.
145. ↑ 145.0 145.1 Semmens, Brice X.; Semmens, Darius J.; Thogmartin, Wayne E.; Wiederholt, Ruscena; López-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.
146. ↑ Conniff, Richard (1 April 2013). "Tracking the Causes of Sharp Decline of the Monarch Butterfly". Yale University.
147. ↑ Wines, Michael (13 March 2013) *Monarch Migration Plunges to Lowest Level in Decades*. *The New York Times*
148. ↑ 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. Archived from the original (PDF) on 4 September 2014.
149. ↑ 149.0 149.1 Brennen, Shannon. "For Love of Nature: Annual monarch butterfly migration in peril". The News & Advance, Lynchburg, Virginia. Retrieved 4 July 2014.
150. ↑ "NRDC Sues EPA Over Demise of Monarch Butterfly Population". NBC. 2015.
151. ↑ Puzey, J. R.; Dalgleish, H. J.; Boyle, J. H. (5 February 2019). "Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops". *Proceedings of the National Academy of Sciences*. **116** (8): 3006–3011. doi:10.1073/pnas.1811437116 . ISSN 0027-8424. PMC 6386695  Check `|pmc=` value (help). PMID 30723147.
152. ↑ 152.0 152.1 Ries, Leslie; Taron, Douglas J.; Rendón-Salinas, Eduardo (2015). "The Disconnect Between Summer and Winter Monarch Trends for the Eastern Migratory Population: Possible Links to Differing Drivers". *Annals of the Entomological Society of America*. **108** (5): 691. doi:10.1093/aesa/sav055.
153. ↑ 153.0 153.1 Inamine, Hidetoshi; Ellner, Stephen P.; Springer, James P.; Agrawal, Anurag A. (2016). "Linking the continental migratory cycle of the monarch butterfly to understand its population decline". *Oikos*. **125** (8): 1081. doi:10.1111/oik.03196 .
154. ↑ 154.0 154.1 Davis, Andrew K. (2012). "Are migratory monarchs really declining in eastern North America? Examining evidence from two fall census programs". *Insect Conservation and Diversity*. **5** (2): 101. doi:10.1111/j.1752-4598.2011.00158.x .
155. ↑ 155.0 155.1 "monarchscience". Akdavis6.wixsite.com. 24 August 2016. Retrieved 6 January 2017.
156. ↑ Mora Alvarez, Blanca Xiomara; Carrera-Treviño, Rogelio; Hobson, Keith A. (2019). "Mortality of Monarch Butterflies (*Danaus plexippus*) at Two Highway Crossing "Hotspots" During Autumn Migration in Northeast Mexico". *Frontiers in Ecology and Evolution*. **7**. doi:10.3389/fevo.2019.00273 . ISSN 2296-701X.
157. ↑ Paz, Fátima (18 June 2014) En espera de aprobación de la Profepa por tala ilegal en la Reserva de la Mariposa Monarca. cambiodemichoacan.com.mx
158. ↑ "Habitat Loss on Breeding Grounds Cause of Monarch Decline, U of G Study Finds". University of Guelph. 4 June 2014. Retrieved 17 March 2015.
159. ↑ Clarke, A. R.; Zalucki, M. P. (2001). "*Taeniogonalos raymenti* Carmean & 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.
160. ↑ 160.0 160.1 Brewer, Jo; Gerard M. Thomas (1966). "Causes of death encountered during rearing of *Danaus plexippus* (Danaidae)" (PDF). *Journal of the Lepidopterists' Society*. **20** (4): 235–238. Archived from the original (PDF) on 25 March 2009. Retrieved 13 April 2008. Lay summary.  Cite uses deprecated parameter `|lay-url=` (help)
161. ↑ 161.0 161.1 Stenoien, Carl; McCoshum, Shaun; Caldwell, Wendy; De Anda, Alma; Oberhauser, Karen (January 2015). "New reports that Monarch butterflies (Lepidoptera: Nymphalidae, Linnaeus) are hosts for a pupal parasitoid (Hymenoptera: Chalcidoidea, Walker)". *Journal of the Kansas Entomological Society*. **88** (1): 16–26. doi:10.2317/JKES1402.22.1.
162. ↑ Leong, K. L. H.; M. A. Yoshimura, H. K. Kaya and H. Williams (1997). "Instar susceptibility of the Monarch butterfly (*Danaus plexippus*) to the neogregarine parasite, *Ophryocystis elektroscirrha*". *Journal of Invertebrate Pathology*. **69** (1): 79–83. CiteSeerX 10.1.1.494.9827 . doi:10.1006/jipa.1996.4634. PMID 9028932.
163. ↑ Bartel, Rebecca; Oberhauser, Karen; De Roode, Jacob; Atizer, Sonya (February 2011). "Monarch butterfly migration and parasite transmission in eastern North America". *Ecology*. **92** (2): 342–351. doi:10.1890/10-0489.1. PMC 7163749  Check `|pmc=` value (help). PMID 21618914.
164. ↑ "Do My Monarch Butterflies Have OE? Ophryocystis elektroscirrha". Butterfly Fun Facts. Retrieved 24 March 2015.
165. ↑ Jepsen, S.; Schweitzer, D. F.; Young, B.; Sears, N.; Ormes, M.; Black, S. H. (2015). *Conservation status and ecology of the monarch butterfly in the United States*. NatureServe. pp. 23–24.
166. ↑ Invasive species alert: Black swallow-wort (*Cynanchum louisea*) and pale swallow-wort (*Cynanchum rossicum*). monarchjointventure.org]
167. ↑ Monarch Population Hits Lowest Point in More Than 20 Years. WWF (29 January 2014)
168. ↑ "Basic Facts About Monarch Butterflies".
169. ↑ Lemoine, Nathan P. (2015). "Climate Change May Alter Breeding Ground Distributions of Eastern Migratory Monarchs (*Danaus plexippus*) via Range Expansion of *Asclepias* Host Plants". *PLOS ONE*. **10** (2): e0118614. Bibcode:2015PLoSO..1018614L. doi:10.1371/journal.pone.0118614 . PMC 4338007 . PMID 25705876.
170. ↑ "monarchscience". Akdavis6.wixsite.com. 10 August 2015.
171. ↑ Hahn, Philip G.; Agrawal, Anurag A.; Sussman, Kira I.; Maron, John L. (January 2019). "Population Variation, Environmental Gradients, and the Evolutionary Ecology of Plant Defense against Herbivory". *The American Naturalist*. **193** (1): 20–34. doi:10.1086/700838. ISSN 1537-5323. PMID 30624107.
172. ↑ "Climate change, pesticides put monarch butterflies at risk of extinction". National Geographic. 21 December 2018. Retrieved 31 December 2018.
173. ↑ "Monarch Butterfly". fws.gov.
174. ↑ Frazin, Rachel (December 15, 2021). "Trump administration punts on protections for monarch butterfly". The Hill. https://thehill.com/policy/energy-environment/530298-trump-administration-punts-on-protections-for-monarch-butterfly. "The Fish and Wildlife Service (FWS) determined that adding the butterfly to the list of threatened and endangered species was “warranted” but that it is unable to do so because it needs to devote its resources to higher-priority species.
The FWS said that its “warranted-but-precluded” 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 aren’t warranted."
175. ↑ (1) Howard, Elizabeth (26 February 2016). "Monarch Population Size Announced". *Journey North*. Archived from the original on 28 February 2016. Retrieved 5 June 2017.
(2) "Eastern Monarch Population Numbers Drop 27%". *News*. The Monarch Joint Venture. 16 February 2017. Archived from the original on 5 June 2017. Retrieved 5 June 2017.
(3) "Where Are All The Monarchs?". *Monarch Lab*. University of Minnesota Extension. 14 July 2016. Archived from the original on 22 August 2016. Retrieved 5 June 2017.
176. ↑ "Another monarch study published showing the spring migration holds the key to everything". *monarchscience*. 4 November 2019. Retrieved 12 December 2019.
"Monarch". Government of Ontario. Retrieved 16 September 2015.
178. ↑ "monarchscience". Akdavis6.wixsite.com. 18 December 2016. Retrieved 12 January 2017.
179. ↑ "Monarchs now listed as an endangered species in Nova Scotia Canada - a prelude for things to come elsewhere". *monarchscience*. 30 September 2019. Retrieved 12 December 2019.
180. ↑ Crewe, Tara L.; Mitchell, Greg W.; Larrivée, 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.
181. ↑ Flockhart, D. T. Tyler; Larrivée, Maxim; Prudic, Kathleen L.; Norris, D. Ryan (21 June 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 .
182. ↑ Obama, President Barack (20 June 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 2 May 2018.
183. ↑ 183.0 183.1 Pollinator Health Task Force (19 May 2015). "National Strategy to Promote the Health of Honey Bees and Other Pollinators" (PDF). Washington, D.C.: The White House. Retrieved 2 May 2018.
184. ↑ (1) "PBS-P100: Facilities Standards for the Public Buildings Service" (PDF). Washington, D.C.: U.S. General Services Administration. March 2015. pp. 42–47. Archived from the original (PDF) on March 19, 2021. Retrieved July 7, 2021.
(2) "P100 Facility Standards For The Public Buildings Service" (PDF). Washington, D.C.: U.S. General Services Administration: Public Buildings Service: Office of the Chief Architect. July 2018. pp. 43–49. Archived from the original (PDF) on July 7, 2021. Retrieved July 7, 2021.
(3) "PBS-P100 Facilities Standards For The Public Buildings Service". *WBDG: Whole Building Design Guide*. Washington, D.C.: National Institute of Building Sciences. July 1, 2018. Archived from the original on April 22, 2021. Retrieved July 7, 2021. 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.
185. ↑ "Public Law 114–94: 114th Congress (129 Stat. 1312–1801)" (PDF). United States Government Publishing Office. Archived from the original (PDF) on June 25, 2021. Retrieved July 7, 2021.
186. ↑ 186.0 186.1 (1) "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 from the original (PDF) on June 25, 2021. Retrieved July 7, 2021. ,
(2) "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 the 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.
(3) 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. Template:PD-notice
187. ↑ (1) "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 from the original (PDF) on September 13, 2021. Retrieved October 6, 2021. }}
(2) "Conservation Reserve Program". United States Department of Agriculture: Farm Service Agency. 2021. Archived from the original on September 17, 2021. Retrieved October 6, 2021.
(3) "Pollinators and monarchs SAFE in Wisconsin". *Newsroom*. United States Department of the Interior: Fish and Wildlife Service. December 29, 2016. Archived from the original on December 23, 2017. Retrieved October 6, 2021.
(4) "Incentive Programs: Conservation Reserve Program (CRP): United States Department of Agriculture Farm Service Agency (FSA)". *Monarch Conservation Toolbox*. Montreal, Quebec, Canada: Commission for Environmental Cooperation. Archived from the original on January 15, 2020. Retrieved October 6, 2021.
188. ↑ (1) Hopwood, Jennifer; Black, Scott; Fleury, Scott (December 2015). *Pollinators and Roadsides: Best Management Practices for Managers and Decision Makers* (PDF). Washington, D.C.: United States Department of Transportation: Federal Highway Administration. OCLC 1252634388. FHWA-HEP-16-020. Archived from the original (PDF) on June 2, 2021. Retrieved July 9, 2021.
(2) Hopwood, Jennifer; Black, Scott; Fleury, Scott (December 2015). *Roadside Best Management Practices that Benefit Pollinators: Handbook for Supporting Pollinators through Roadside Maintenance and Landscape Design* (PDF). Washington, D.C.: United States Department of Transportation: Federal Highway Administration. OCLC 1252634401. FHWA-HEP-16-059. Archived from the original (PDF) on June 1, 2021.
(3) Remley, Deirdre; Redmon, Allison (September 2017). "Save The Bees and Butterflies!". *Public Roads*. Washington, D.C.: United States Department of Transportation: Federal Highway Administration. **81** (2). FHWA-HRT-17-006. Archived from the original on November 12, 2020.
(4) Renkl, Margaret (September 16, 2019). "Tennessee Makes Way for Monarchs". *The New York Times*. https://www.nytimes.com/2019/09/16/opinion/tennessee-wildflowers-nature.html.
189. ↑ (1) National Academies of Sciences, Engineering, and Medicine (2020). *Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies*. Washington, D.C.: National Academies Press. doi:10.17226/25693. ISBN 9780309481328. LCCN 2020935714. OCLC 1229163481. National Cooperative Highway Research Program (NCRHP) Research Report 942. Archived from the original on July 29, 2020. Retrieved July 8, 2021. CS1 maint: Multiple names: authors list (link)
(2) Cariveau, A.B.; Caldwell, W.; Lonsdorf, E.; Nootenboom, C.; Tuerk, K.; Snell-Rood, E.; Anderson, E.; Baum, K. A.; Hopwood, J.; Oberhauser, K. (2019). "Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies" (PDF). Washington, D.C: Transportation Research Board. OCLC 1152199695. Pre-publication draft of NCHRP Research Report 942. Archived from the original (PDF) on July 8, 2021. Retrieved July 8, 2021 – via Northwestern University Library.
190. ↑ Davis, Andrew K.; Schroeder, Hayley; Yeager, Ian; Pearce, Jana (31 May 2018). "Effects of simulated highway noise on heart rates of larval monarch butterflies, *Danaus plexippus*: implications for roadside habitat suitability". *Biology Letters*. **14** (5): 20180018. doi:10.1098/rsbl.2018.0018. PMC 6012697  Check `|pmc=` value (help). PMID 29743264.
191. ↑ 191.0 191.1 Cariveau, A.B.; Caldwell, W.; Lonsdorf, E.; Nootenboom, C.; Tuerk, K.; Snell-Rood, E.; Anderson, E.; Baum, K. A.; Hopwood, J.; Oberhauser, K. (2019). "Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies" (PDF). Washington, D.C: Transportation Research Board. pp. 2–3. OCLC 1152199695. Pre-publication draft of NCHRP Research Report 942. Archived from the original (PDF) on July 8, 2021. Retrieved July 8, 2021 – via Northwestern University Library.
192. ↑ (1) Glassberg, J. (1995). *Enjoying butterflies more: attract butterflies to your backyard*. Marietta, Ohio: Bird Watcher's Digest Press. ISBN 1880241080. LCCN 96202681. OCLC 35808599. Retrieved 9 March 2020 – via Google Books.
(2) "Butterfly Gardening: Introduction". University of Kansas: Monarch Watch. Archived from the original on 2 February 2020. Retrieved 9 March 2020.
(3) "Monarch Garden Plants" (PDF). San Francisco, California: Pollinator Partnership. Archived from the original (PDF) on 9 March 2020. Retrieved 9 March 2020.
(4) "Monarch Waystation Program". University of Kansas: Monarch Watch. Archived from the original on 2 June 2017. Retrieved 5 June 2017.
(5) Abugattas, Alonzo (3 January 2017). "Monarch Way Stations". Archived from the original on 5 June 2017. Retrieved 5 June 2017 – via Blogger.
(6) "Plants for Butterfly and Pollinator Gardens: Native and Non-native Plants Suitable for Gardens in the Northeastern United States" (PDF). Monarch Watch. Archived from the original (PDF) on 9 August 2020. Retrieved 18 October 2020.
(7) Wheeler, Justin (November 21, 2017). "Picking Plants for Pollinators: The Cultivar Conundrum". *Xerces Blog*. The Xerces Society for Invertebrate Conservation. Archived from the original on April 14, 2021. Retrieved August 1, 2021.
193. ↑ (1) Borders, Brianna; Lee–Mäder, Eric (2014). "Milkweed Propagation and Seed Production" (PDF). *Milkweeds: A Conservation Practitioner's Guide: Plant Ecology, Seed Production Methods, and Habitat Restoration Opportunities*. Portland, Oregon: The Xerces Society for Invertebrate Conservation. pp. 21–95. Archived from the original (PDF) on July 4, 2021. Retrieved July 12, 2021.
(2) Landis, Thomas D.; Dumroese, R. Kasten (2015). "Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat" (PDF). *International Plant Propagators' Society, Combined Proceedings (2014)*. **64**: 299–307. Archived from the original (PDF) on March 8, 2021. Retrieved July 11, 2021 – via United States Department of Agriculture: United States Forest Service.
194. ↑ (1) National Academies of Sciences, Engineering, and Medicine (2020). *Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies*. Washington, D.C.: National Academies Press. pp. 79–80. doi:10.17226/25693. ISBN 9780309481328. LCCN 2020935714. OCLC 1229163481. National Cooperative Highway Research Program (NCRHP) Research Report 942. Archived from the original on July 29, 2020. Retrieved July 8, 2021. ***Could roadside mowing stimulate milkweed growth and support monarch breeding?*** Limited research in eastern North America has shown that spring or summer mowing can promote new growth and extend the availability of milkweed plants for monarch breeding. Mowing may stimulate growth of some milkweed species, particularly those that spread through rhizomes like common milkweed (*A. syriaca*) and showy milkweed (*A. speciosa*). Summer (June or July) mowing in Michigan resulted in more monarch eggs on regenerated stems than unmowed stems. Summer (July) mowing and burning can increase green antelopehorn milkweed (*A. viridis*) availability in the late summer and early fall in the Southern Great Plains, whereas in areas without mowing, the milkweed has senesced by August. In the West, showy milkweed will regrow after summer mowing and continue to support monarch breeding (Stephanie McKnight, personal observation). However, more research is needed in other areas to determine the optimal timing and frequency of mowing that promotes not only milkweed but also nectar plants. It is also unknown if the benefit of additional milkweed availability in the fall outweighs the costs of the larval mortality caused by summer mowing. The benefits are likely greater in areas that primarily have breeding monarchs in the spring and fall and where the dominant species of milkweed spread by rhizomes. *Sources: Alcock et al. 2016; Baum and Mueller, 2015; Bhowick 1994; Haan and Landis 2019; Fischer et al. 2015* CS1 maint: Multiple names: authors list (link)
(2) Higgins, Adrian (27 May 2015). "A gardener's guide to saving the monarch". *Home & Garden* (The Washington Post). http://www.washingtonpost.com/lifestyle/home/creating-a-rest-stop-for-the-monarch/2015/05/26/cd81a75c-ffcb-11e4-805c-c3f407e5a9e9\_story.html. ""The monarch doesn't care where the milkweed grows, and putting it in residential neighborhoods makes perfect sense," said Doug Tallamy, an entomologist at the University of Delaware, author and expert on wildlife habitat gardens. ....
The Smithsonian Institution's Butterfly Habitat Garden .... and the Ripley Garden .... are both good places to see milkweed integrated into a garden setting.
 At the butterfly garden, you can see the common milkweed ... now looking pretty good in fresh, unblemished clumps. By late summer, it looks tall, tired and tough. Tallamy says if you grow it, you should cut it back at least by half in June to produce soft foliage in late summer that will be more munchable for the caterpillars. If you do that, make sure there are no larvae on the plant before you chop it."
(3) Abugattas, Alonzo (3 January 2017). "Monarch Way Stations". *Capital Naturalist*. Archived from the original on 8 March 2021. Retrieved 5 July 2021 – via Blogger. Virginia is blessed for instance with 13 native Asclepias species plus 4 climbing vines that Monarch caterpillars can feed on. For the best results, cut the some of the stems back in late summer after they've bloomed. Fall is the when we get the most Monarchs laying eggs on our milkweeds. Since the mother butterflies prefer young, more tender growth, you can provide this by timing your pruning so there are new leaves by September or so for the arriving Monarchs. Just make sure to leave a few to produce pods for seeds. The local monarch favorite is Common Milkweed (A. syriaca), .....
(4) Gomez, Tony. "*Asclepias syriaca*: Common Milkweed for Monarch Caterpillars". *Monarch Butterfly Garden*. MonarchButterflyGarden.net. Archived from the original on 16 March 2015. Retrieved 17 October 2010. Cut- At mid season after the blooms have faded, cut some common plants back by about a third. This promotes fresh plant growth and could get you an extra generation of monarchs on the fresh new leaves. Leave some plants uncut if you want to harvest milkweed seeds in fall. .
(5) Stevens, Michelle. "Plant guide for common milkweed (Asclepias syriaca)" (PDF). United States Department of Agriculture: Natural Resources Conservation Service: National Plant Data Center. Archived from the original (PDF) on July 5, 2021. Retrieved July 5, 2021.
195. ↑ (1) Borders, Brianna; Lee–Mäder, Eric (2014). "Milkweed Propagation and Seed Production: Stratification" (PDF). *Milkweeds: A Conservation Practitioner's Guide: Plant Ecology, Seed Production Methods, and Habitat Restoration Opportunities*. Portland, Oregon: The Xerces Society for Invertebrate Conservation. pp. 28–29. Archived from the original (PDF) on July 4, 2021. Retrieved July 12, 2021.
(2) Landis, Thomas D.; Dumroese, R. Kasten (2015). "Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat" (PDF). *International Plant Propagators' Society, Combined Proceedings (2014)*. **64**: 302. Archived from the original (PDF) on March 8, 2021. Retrieved July 11, 2021 – via United States Department of Agriculture: United States Forest Service. Many sources of milkweed seeds require stratification (cold, moist treatment) before sowing. In a review of stratification requirements for common milkweed, recommendations varied from as short as 7 days to as long as 11 months at 5°C (41°F) (Luna and Dumroese, 2013). Butterfly milkweed (A. tuberosa) germination increased from 29 to 48 to 62% as stratification duration increased from 0 to 30 to 60 days, respectively (Bir, 1986). Our informal natural stratification trial with showy (milkweed) and narrow leaf milkweed (A. fascicularis) in southern Oregon revealed that seeds began to germinate after 15 weeks in stratification (Fig. 3A).
(3) Higgins, Adrian (27 May 2015). "7 milkweed varieties and where to find them". *Home & Garden* (The Washington Post). https://www.washingtonpost.com/lifestyle/home/a-world-of-milkweeds/2015/05/26/43fba7d6-fe6c-11e4-833c-a2de05b6b2a4\_story.html. "Seed may be stubborn to germinate and may need a period of cold treatment." .
(4) Gomez, Tony. "*Asclepias syriaca*: Common Milkweed for Monarch Caterpillars". *Monarch Butterfly Garden*. MonarchButterflyGarden.net. Archived from the original on March 16, 2015. Retrieved October 17, 2010. Start seeds indoors 2 months before final frost- seeds must be cold stratified. .
(5) Stevens, Michelle. "Plant guide for common milkweed (Asclepias syriaca)" (PDF). United States Department of Agriculture: Natural Resources Conservation Service: National Plant Data Center. Archived from the original (PDF) on July 5, 2021. Retrieved July 5, 2021. If planting in flats or in a greenhouse, common milkweed seeds should be cold-treated for three months.
(6) "*Asclepias syriaca*". *Butterfly gardening & all things milkweed*. Archived from the original on 7 July 2015. Retrieved July 7, 2015. germination: seed requires cold moist period.
196. ↑ (1) Mader, Eric; Shepherd, Mathew; Vaughan, Mace; Black, Scott Hoffman; LeBuhn, Gretchen (2011). *Attracting Native Pollinators: Protecting North America's Bees and Butterflies: The Xerces Society guide*. North Adams, Massachusetts: Storey Publishing. pp. 113–114. ISBN 9781603427470. LCCN 2010043054. OCLC 776997073. Retrieved July 7, 2021 – via Internet Archive.
(2) Landis, Thomas D.; Dumroese, R. Kasten (2015). "Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat" (PDF). *International Plant Propagators' Society, Combined Proceedings (2014)*. **64**: 302. Archived from the original (PDF) on March 8, 2021. Retrieved July 11, 2021 – via United States Department of Agriculture: United States Forest Service. Any of the standard seed propagation methods (Landis et al., 1999) are effective with milkweed. Direct sowing of non-stratified seeds during the fall followed by exposure to ambient winter conditions can be effective, but the seeds must be mulched and protected. Cover sown seeds with a thin mulch; research has found that common milkweed seeds germinated better when planted 1 to 2 cm (0.4 to 0.8 in.) deep than when at the soil surface (Jeffery and Robison, 1971).
197. ↑ Bush-Brown, James; Bush-Brown, Louise (1958). "Chapter 32: Mulches". *America's garden book*. New York: Charles Scribner's Sons. p. 768. LCCN 58005738. OCLC 597041748 – via Internet Archive.
198. ↑ 198.0 198.1 Gomez, Tony. "*Asclepias tuberosa*: Butterfly Weed for Monarchs and More". *Monarch Butterfly Garden*. MonarchButterflyGarden.net. Archived from the original on July 29, 2016. Retrieved 17 October 2010. Rough leaves for monarch caterpillars, not typically a heavily used host plant
199. ↑ (1) 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 (ESA). **9** (1): 1–13. doi:10.1002/ecs2.2064. Retrieved July 6, 2021 – via Wiley Online Library.
(2) "Asclepias incarnata". *North Carolina Extension Gardener Plant Toolbox*. Raleigh, North Carolina: North Carolina State University: N.C. Cooperative Extension. Archived from the original on November 28, 2020. Use in a naturalized area, pollinator garden or along a pond or stream in full sun to partial shade.
(3) "Asclepias incarnata". St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on February 25, 2021. Retrieved July 5, 2021. **Uses**: Sunny borders, stream/pond banks, butterfly gardens.
(4) Gomez, Tony. "Asclepias Incarnata: Swamp Milkweed for Monarch Butterflies and Caterpillars". *Monarch Butterfly Garden*. Archived from the original on April 22, 2021. Retrieved July 5, 2021.
(5) Vogt, Benjamin (February 19, 2015). "Great Design Plant: Asclepias Incarnata for a Butterfly Garden: Beautiful swamp milkweed makes it easy to help monarchs and other pollinators in eastern U.S. gardens". Palo Alto, California: Houzz. Archived from the original on May 7, 2021. Retrieved July 5, 2021.
(6) Abugattas, Alonzo (3 January 2017). "Monarch Way Stations". *Capital Naturalist*. Archived from the original on 8 March 2021. Retrieved 5 July 2021 – via Blogger. A better option for most gardeners might be Swamp Milkweed (*A. incarnata*) which, despite its name, does fine in regular garden soil and doesn’t spread by runners.
200. ↑ Abugattas, Alonzo (3 January 2017). "Monarch Way Stations". *Capital Naturalist*. Archived from the original on 8 March 2021. Retrieved 5 July 2021 – via Blogger. A better option for most gardeners might be Swamp Milkweed (*A. incarnata*) which, despite its name, does fine in regular garden soil and doesn’t spread by runners.
201. ↑ 201.0 201.1 "Asclepias incarnata". *Bring Back The Monarchs*. Monarch Watch. Archived from the original on June 12, 2021. Retrieved July 5, 2021. **Life span**: In gardens most plants live two-five years but known to survive up to 20 years. ....  **Propagation**: Slow to spread via seeds. .... '**Overhead Conditions**: Not shade tolerant. An early successional plant that tends to grow at the margins of wetlands and in seasonally flooded areas. It is not a good vegetative competitor and tends to disappear as vegetative density increases and habitats dry out.

## 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