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Overview

Brief Summary

Introduction

The monarch is one of the best known butterfly species. Although native to North and South America, it has expanded its distribution to Australia, many Pacific islands, and a few places in Europe. Monarch larvae, like those of many other Danaini, feed on milkweeds of the family Asclepiadaceae, from which they sequester cardiac glycosides that often render them unpalatable to potential predators. The species is perhaps best known for its annual migrations, from eastern North America to the mountains of central Mexico, and from western North America to the coast of California. The butterflies rest for the cool winter months in large aggregations which may contain tens of millions of individuals.

Left: Monarch larva feeding on milkweed host plant at Poco Sol (Caribbean slope below Monteverde), Costa Rica. Right: Overwintering monarchs covering a tree branch at Alpha Monarch research site, Mexico. Images © Greg and Marybeth Dimijian

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North American Ecology (US and Canada)

Danaus plexippus is a year-round resident in Calif. and s. Fla. and migratory through most of North America (Scott 1986). The eastern population exhibits a fantastic and unique migratory habit, with adults overwintering in a small forest are in central Mexico and spring migrants laying eggs and expanding over several generations until they reach Canada in late summer. California populations overwinter in forest stands along the coast and migrate inward. Populations in south Florida do not migrate. Breeding habitats are mostly open places, esp. moist valley bottoms, breeding from the subtropics to the lower Canadian zone. Host plants are herbaceous and include many species but restricted mostly to family Asclepiadaceae. Eggs are laid on the host plant singly. Individuals overwinter as adults, by roosting in trees. There are five or more flights all year in Calif. and s. Fla.; in New Mexico and s. Nev. several flights Mar.10-Nov.30; in the northeast May1-Oct31; in Nfld, Aug1-Oct.31. (Scott 1986).
  • Scott, J. A. 1986. The butterflies of North America. Stanford University Press.
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Comprehensive Description

General Description

The black-veined, orange upperside with a white-spotted black border is unique. The Viceroy (Limenitis archippus) though similar, has a black hindwing median line. Monarchs are easy to recognize by their distinctive leisurely, floating flight, holding their wings V-shaped above the body when gliding; Viceroys hold their wings in a flat plane when gliding, a behaviour characteristic of the genus Limenitis.
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Distribution

Globally widespread, with the centre of the range in North America from BC east to Newfoundland, north to the southern NWT south to Argentina (Layberry et al 1998).
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) The Monarch butterfly is attaining near worldwide distribution in suitable places, but is primarily a species of the Americas. Autumnal migrants occasionally stray to Europe including England; the species has been spread widely in the Pacific Ocean area and is well-established in Australia. However, the seasonal ranges in North America are vastly different, by millions of square kilometers. Essential overwintering areas for North American populations are limited to a few dozen places in coastal California and the mountains of Mexico. Specifically that means that the summer range includes portions of up to 49 of the 50 US states and southern portions of all Canadian Provinces bordering the US where milkweeds occur. However the winter range includes none of Canada and in the US only a few dozen square kilometers in California, and at least some years a bit of south Florida. Florida winter populations may be non-migratory and if so contribut little to summer populations. Some winters a few may persist in sothern Arizona.

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Geographic Range

Monarch butterflies are found in North America, South America, the Caribbean, Australia, New Zealand, islands in the Pacific Ocean, Mauritius, the Canary Islands of the Atlantic, and Western Europe.

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Physical Description

Morphology

Physical Description

Both male and female monarchs are bright orange with black borders and black veins. The veins on the female are thicker than those of the male. Male monarchs also have a swollen pouch on both of their hind wings.

Monarchs are poisonous to vertebrates. Their poison comes from the milkweed they feed on.

Monarchs also use their appearance to ward off predators. Orange is considered a warning color, which will warn predators that monarchs are poisonous, and not to attack them. From a distance, monarchs can blend into their surroundings. Sometimes, their spots will appear to be the eyes of a larger animal, and will ward off predators.

Range wingspan: 8.6 to 12.4 cm.

Other Physical Features: ectothermic ; bilateral symmetry ; poisonous

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Diagnostic Description

Monarch butterflies have a wingspan of 3-4 1/2 inches (75-114 mm). The male is bright orange and has a black scent patch in the middle of the upper hind wing. The female is dull orange or brown with more thickly scaled black veins. The underside of the hind wing is light orange with black veins and a marginal black border with two rows of white spots. The upper front wing has a black apex (tip) with white spots. The sub-apex has light orange spots on a dark background. The underside of the front wing has white spots and yellow ovals in the outer portion.

  • Opler, P. A. and A. Bartlett Wright. 1999. Western Butterflies. Peterson Field Guides. Houghton Mifflin Co., Boston, New York.
  • Stewart, B., P. Brodkin, and H. Brodkin. 2001. Butterflies of Arizona. A Photographic Guide. West Coast Lady Press, Arcata, CA.
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Ecology

Habitat

Comments: Habitat is a complex issue for this species. In general breeding areas are virtually all patches of milkweed in North America and some other regions. The critical conservation feature for North American populations is the overwintering habitats, which are certain high altitude Mexican conifer forests or coastal California conifer or Eucalyptus groves as identified in literature. It appears virtually all North American monarchs overwinter in one of these two areas. Lethal cold would preclude successful overwintering in places like the Gulf Coast and much of Florida some years and it appears thse are not major wintering regions as used to be assumed. In addition certain major coastal migratory stopovers may be important conservation sites especially those in along Delaware Bay in New Jersey including Cape May where adults may holdover for several days awaiting suitable conditions for crossing the Bay. There are major, but probably less important, roosting sites farther north such as east of New Haven and probably others farther south perhaps even as far as Cuba. Coastal regions are important flyways and so nectar (wild or in gardens) is an important reseource in such places. In places like Hawaii and some others the species simply breeds year round and is not really migratory.

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Monarch butterflies prefer warmer climates; they cannot tolerate frost. They like open country. Females spend much of their time around searching for or staying near the main food plant for the caterpillars (see food habits section). Monarch butterflies require thick tree covering during the winter. In California, they live in eucalyptus trees. These eucalyptus trees are not normally found in California, but were put there to replace trees that had been cut down.  Biomes: temperate forest and rainforest, temperate grassland, chaparral, tropical rainforest, tropical deciduous forest, tropical scrub forest, tropical savanna and grasslands, mountains

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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

The main larval host in Alberta is Showy Milkweed (Asclepias speciosa), and larvae have also been recorded on A. ovalifolia in Edmonton (Bird et al. 1995). Adults prefer nectaring at milkweed flowers and composites (Klassen et al. 1989).
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Comments: Larval foodplants are milkweeds.

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Food Habits

Monarch females lay their eggs on milkweed plants (Asclepias), these plants are then the main food for the caterpillars. Adult monarchs feed on nectar from many kinds of flowers.

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Associations

Flowering Plants Visited by Danaus plexippus in Illinois

Danaus plexippus Linnaeus: Nymphalidae, Lepidoptera
(observations are from Robertson, Graenicher, Betz et al., Reed, Hilty, Clinebell, Smith & Snow, Hapeman, Macior, Broyles & Wyatt, Willson & Bertin, Fothergill & Vaughn; this is the Monarch butterfly)

Apiaceae: Eryngium yuccifolium sn (Rb), Pastinaca sativa sn (Rb), Sium suave sn (Rb), Torilis arvensis sn (FV); Asclepiadaceae: Ampelamus albidus [plup sn] (H), Asclepias exaltata [plup sn] (BW), Asclepias incarnata [plpr sn] [plup sn] (Rb, Btz), Asclepias syriaca [plpr sn] (Rb), Asclepias tuberosa [plab] [plup] (Rb, Btz, H), Asclepias verticillata [plpr sn] [plup sn] (Rb, WB); Asteraceae: Aster drummondii sn (Gr), Aster furcatus sn (Gr), Aster laevis sn (Gr), Aster lanceolatus sn (Gr), Aster macrophyllus sn (Gr), Aster novae-angliae sn (Rb, Gr, H), Aster pilosus sn (Rb), Aster puniceus sn (Gr), Aster salicifolius sn (Rb), Bidens aristosa sn (Rb), Bidens cernua sn fq (Rb), Boltonia asterioides sn (Rb), Cirsium altissimum sn (Gr), Cirsium discolor sn (Rb, H), Cirsium hillii sn (Rb), Cirsium vulgare sn (Rb, Gr), Conoclinium coelestinum sn (Rb), Coreopsis tripteris sn (Rb), Echinacea pallida sn (Rb), Echinacea purpurea sn (Rb, H), Eupatoriadelphus purpureus sn (Rb, Gr, H), Eupatorium altissimum sn (H), Eupatorium perfoliatum sn (Rb, Gr), Euthamia graminifolia sn (Gr), Helianthus annuus sn (Rb, H), Helianthus grosseserratus sn fq (Rb), Helianthus mollis sn (H), Helianthus strumosus sn (Gr), Heliopsis helianthoides sn (Gr), Liatris aspera sn (Rb, H), Liatris pycnostachya sn (Rb), Liatris spicata sn (Gr), Oligoneuron rigidum sn (H, Re), Rudbeckia laciniata sn (Gr), Silphium integrifolium sn (H), Silphium laciniatum sn (Rb), Silphium perfoliatum sn (Rb), Silphium terebinthinaceum sn (H), Solidago canadensis sn (Rb, Gr), Solidago nemoralis sn (Rb), Taraxacum officinale sn (FV), Vernonia fasciculata sn (Rb); Boraginaceae: Mertensia virginica sn (Rb); Campanulaceae: Lobelia siphilitica sn (Rb); Caprifoliaceae: Symphoricarpos albus sn (Gr), Symphoricarpos occidentalis sn (Gr); Dipsacaceae: Dipsacus fullonum sn (Rb); Fabaceae: Melilotus alba sn (Rb), Robinia pseudoacacia sn np (Rb), Trifolium pratense sn (Rb), Trfiolium repens sn (FV); Lamiaceae: Agastache nepetoides sn (Rb), Blephilia hirsuta sn (Rb), Monarda fistulosa sn (Rb, Cl), Physostegia virginiana sn np (Rb), Salvia azurea sn np (H); Liliaceae: Lilium michiganense sn (Rb); Orchidaceae: Platanthera blephariglottis sn (SS), Platanthera ciliaris sn (SS), Platanthera peramoena sn (Hpm); Polemoniaceae: Phlox divaricata laphamii sn (Rb), Phlox glaberrima sn (Rb); Polygonaceae: Persicaria pensylvanica sn (H); Ranunculaceae: Delphinium tricorne sn np (Rb, Mc); Rosaceae: Crataegus crus-galli sn (Rb), Crataegus intricata sn (Rb), Malus coronaria sn (Rb), Prunus americana sn (Rb), Prunus serotina [flwr sn] (Rb); Rubiaceae: Cephalanthus occidentalis sn fq (Rb); Verbenaceae: Verbena stricta sn (Rb); Violaceae: Viola sororia sn (FV)

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: This refers to global occurrences for the species as a whole and includes introduced populations in Hawaii, Australia etc., as well as central and South America. In these places and where non-migratory native populations occur, habitat may be more or less used all year. North American populations also have a lot of breeding habitat, most of it patchy and suboptimally managed for Monarch survival, but still producing millions of adults each summer. These face an annual bottleneck in terms of dependence on a few dozen overwintering areas. Western North American populations may also be under pressure from scarcity of good breeding sites, especially in dry years, and incompatible management.

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Global Abundance

>1,000,000 individuals

Comments: At least millions of individuals, probably more than a billion in many years, worldwide.

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General Ecology

Can contain poison derived from their larval foodplant that helps avoid predation by birds (Scott, 1986).

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Life History and Behavior

Behavior

Adults feed mainly on flower nectar. Males patrol for females (Scott, 1986).
  • Scott, J. A. 1986. The butterflies of North America. Stanford University Press.
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Cyclicity

Migrants reach southern Alberta in late May to June, offspring emerging in Aug. to Sep.
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Life Cycle

Migrants from the southern US appear in the spring, and lay eggs on a number of milkweed species, particularly along prairie river valleys. Larvae are like no other in Alberta, boldly banded with alternating black, white and yellow stripes. There are two long, black fleshy 'horns' near the front and rear. Pupae are bright blue-green with golden spots. This is undoubtedly one of the most familiar butterflies in North America, and much research has been carried out on its ecology and remarkble migration. Surprisingly, the Monarch's wintering grounds in Mexico were not discovered until 1975, largely as a result of the research efforts of Fred Urquhart (Layberry et al. 1998). Almost all of the North American Monarchs overwinter in a handful of sites in the Mexican highlands, and conservation efforts for this species are largely dependent on the welfare of these sites. For more detailed accounts of the Monarch's ecology, see Brower (1995) and references therein.
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Development

Small caterpillars hatch from eggs laid by female Monarchs. They grow, shedding their skin to get bigger. Eventually each caterpillar stops growing and forms a case around itself called a chrysalis. Inside the chrysalis it changes its body its body in a process called metamorphosis. When it is done it emerges as an adult butterfly.

Development - Life Cycle: metamorphosis

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Reproduction

In Baja California may be encountered throughout the year (November-April in coastal regions and June-October in the Mountains) (Brown et al., 1992)

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The mating period occurs in the spring, just prior to migration from the overwintering sites. The courtship of Danaus plexippus is fairly simple and less dependent on chemical pheromones in comparison with other species in its genus. Courtship is composed of two distinct stages, the aerial phase and the ground phase. During the aerial phase, the male pursues, nudges, and eventually takes down the female. Copulation occurs during the ground phase and involves the transfer of a spermatophore from the male to female. Along with sperm, the spermatophore is thought to provide the female with energy resources that aid her in carrying out reproduction and remigration.

Breeding interval: Monarch butterflies mate in the spring before they migrate.

Key Reproductive Features: semelparous ; sexual ; fertilization (Internal ); oviparous

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Danaus plexippus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 18
Specimens with Barcodes: 82
Species With Barcodes: 1
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Barcode data: Danaus plexippus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 39 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

CGAATAAATAATATAAGATTTTGACTTTTACCCCCATCATTAATTYTATTAATTTCAAGAAGAATCGTAGAAAATGGTGCAGGAACAGGATGAACAGTTTACCCCCCACTTTCATCAAATATTGCTCATAGAGGATCTTCTGTAGATCTA---GCTATTTTTTCTTTACATTTAGCTGGAATTTCATCTATTTTAGGAGCTATTAATTTTATTACTACAATCTTAAATATACGAATTAATAATATAACATTTGATCAAATACCTTTATTTGTTTGAGCAGTAGGTATTACAGCTCTTCTTTTATTACTTTCTTTACCAGTTTTAGCAGGA---GCAATTACTATACTTCTTACTGATCGAAATTTAAATACTTCTTTTTTTGATCCTGCTGGTGGAGGAGACCCTATTTTATATCAACATTTATTTTGATTTTTCGGTCATCCTGAAGTTTATATTTTAATTTTACCAGGATTTGGAATAATTTCTCATATTATTTCTCAAGAAAGAGGAAAAAAA---GAAACCTTTGGTTCTTTAGGAATAATTTATGCTATAATAGCAATTGGTCTTCTTGGATTTATTGTTTGAGCTCATCATATATTTACTGTTGGTATAGATATTGATACTCGAGCTTATTTCACTTCTGCAACTATAATTATTGCTGTACCAACAGGAATTAAAATTTTTAGATGATTA---GCTACTATTCACGGAACA---CAAATTAATTACAGACCTTCTATTTTATGAAGACTTGGATTTGTATTTTTATTTACTGTAGGAGGATTAACAGGAGTAGTTTTAGCCAATTCTTCTATTGATATTACTCTTCATGATACTTATTATGTAGTAGCTCATTTTCATTATGTT---TTATCTATAGGAGCTGTATTTGCTATTTTAGGAGGATTTATTCACTGATATCCTCTTTTTACAGGTTTAACTCTTAATCCTTAYTTATTAAAAATTCAATTTATTTCTATATTCTTAGGAGTAAAT
-- end --

Download FASTA File
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Conservation

Conservation Status

The Monarch is of special concern in Canada (COSEWIC 2002).
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National NatureServe Conservation Status

Canada

Rounded National Status Rank: N5B - Secure

United States

Rounded National Status Rank: N5B,N2N : N5B: Secure - Breeding, N2N: Imperiled - Nonbreeding

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

Reasons: The Monarch is globally secure, because it is doing well in many places where populations are not native and/or not strongly migratory, which drives the G5 rank. However, this is misleading in North America where the Monarch is no longer secure because of serious threats to their obligate overwintering areas in Mexico (mostly) and and a recent order of magnitude decline in California based population, which apparently reflects threats in the western breeding range. Threats also exist in the eastern spring migration route (especially in Texas). The migratory North American populations have been declining in recent years with 2009 among the worst ever (2010 data not evaluated) for California winter population. Deteriorating spring climate conditions in Texas appear to be a major contributor to recently declining numbers in the eastern US in the 2000s. Western North American populations are probably more threatened than eastern ones because suitable milkweeds are less reliable in generally more arid western regions in dry periods. Rank Calculator v3.0 is also G5. Regardless of the fate of North american populations, the species as a whole is globally secure.

Environmental Specificity: Broad. Generalist or community with all key requirements common.

Comments: Very broad as a breeder everywhere and globally overall, but very narrow for overwintering populations in North America.

Other Considerations: Elimination of Mexican sites would mean virtual extinction of eastern North American populations. Nearly all western individuals had been thought to winter in California, but some of these also go to th mountains of Mexico. This species has become a significant ecotourism resource locally in Mexico.

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The places where monarchs spend the winter are threatened. The United States and Mexico are trying to help the areas where monarch butterflies migrate.

IUCN Red List of Threatened Species: no special status

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

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Global Short Term Trend: Increase of 10-25% to decline of 30%

Comments: Difficult to assess globally. Stable to increasing in many places where it is not native and in some Neotropical places where it is. North American populations, which are still a large portion of the global total, are well documented to be declining, but fluctuate from year to year. California based populations may be down more than 90% from 1997-2009.

Global Long Term Trend: Increase of >25% to decline of 50%

Comments: See short term.

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Threats

Degree of Threat: Medium

Comments: The species as a whole is not seriously threatened, but the typical subspecies may be secure mostly where it is not native. The monarch appears to be doing well or even increasing in may places, but not in its core North American range. The native eastern North American populations are in trouble at their overwintering grounds. Overwintering habitats in Mexico are primarily in a few hectares each and have been under pressure from logging, agricultural and urban development. California based populations are declining more due to problems in the breeding areas. Climate change is emerging as a current, rather than an expected, threat in Mexico, California, and Texas at least. There was some improvement in the eastern, as well as western, USA in 2010 so at least populations can still respond quickly to temporarily good conditions. Regardless of what happens in North America this species is at virtually no risk of global extinction in the forseeable future.

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Management

Biological Research Needs: The basics of Monarch biology, migration, etc. are now rather well known, although some of the details regarding western US populations may still need resolution. Main needs now appear to be understanding impacts of and how to prevent or mitigate habitat changes and climate change primarily in overwintering areas and during spring migration particularly in Texas. Accurate information for Central and South America needs to be compiled, because this is globally significant to the species even if unrelated to its status in North America.

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Global Protection: Unknown whether any occurrences are appropriately protected and managed

Comments: Too difficult to assess because needs vary so widely with local ecology.

Needs: Winter habitats in California and Mexico need protection from logging, development, etc. This need has been known for decades. In the near term mitigation of climate change impacts could become an urgent need.

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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Positive

Some milkweed plants are poisonous to cattle. Monarch butterflies help reduce the amount of these plants.

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Pollinator

Compared to bees, butterflies are often less efficient at transferring pollen between plants because pollen often does not stick to their bodies and they lack specialized structures for collecting pollen. However, on the occasions in which pollen does stick to the butterflies' bodies, it is often inadvertently transferred to another flower while the butterflies are nectaring, earning them the title of pollinators.

Research has shown that most butterfly species do indeed end up pollinating some of the flowers they visit, and because monarch butterflies have such a long migration route they are potential pollinators to plants across the country! Studies have found that monarch butterflies do carry pollen from swamp milkweed (Asclepias incarnata) and are, therefore, potential pollinators. Monarch butterflies are known pollinators of common milkweed (Asclepias syriaca), butterfly weed (Asclepias tuberosa), and rattlesnake master (Eryngium yuccifolium). Additionally, monarch butterflies feed on the nectar of many other plants, like rabbitbrush (Ericameria nauseosa), desert broom (Baccharis spp.), aster (Aster spp.), sunflower (Helianthus spp.), goldenrod (Solidago spp.), verbena (Verbena spp.), clover (Trifolium spp.), and other milkweed species (Asclepias spp.).

Although adult monarchs feed on the nectar of many flowers, they will breed only where milkweed plants are found. That is because monarch larvae feed exclusively on milkweed plants. Milkweed plants contain compounds called cardenolide alkaloids that are toxic to most vertebrate herbivores if ingested. However, while monarch larvae feed on milkweed plants they also ingest the toxins. They then sequester the compounds in their bodies, wings, and exoskeletons, making both the larvae and adult butterflies toxic to many predators.

  • The Monarch Butterfly in North America, US Forest Service
  • Diversity and temporal change in the effective pollinators of Asclepias tuberosa, D. L. Venable, Ecology, Vol. 77, No. 4, 1996, p. 1061-1073, Pollinator Conservation Digital Library
  • Migratory Pollinators Program: Monarch Butterfly (Danaus plexippus), Arizona-Sonora Desert Museum
  • Reproductive biology of Eryngium yuccifolium (Apiaceae), a prairie species, Brenda Molano-Flores, Journal of the Torrey Botanical Society, Vol. 128, No. 1, 2001, p. 1-6, Pollinator Conservation Digital Library
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Wikipedia

Monarch butterfly

The monarch butterfly (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. It may be the most familiar North American butterfly. 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.[3] Its wings feature an easily recognizable orange and black pattern, with a wingspan of 8.9–10.2 cm (3½–4 in).[4] (The viceroy butterfly is similar in color and pattern, but is markedly smaller, and has an extra black stripe across the hind wing.) Female monarchs have darker veins on their wings, and the males have a spot called the androconium in the center of each hind wing.[5] Males are also slightly larger than female monarchs.

The eastern North American monarch population is notable for its southward late summer/autumn migration from the United States and southern Canada to Mexico, covering thousands of miles. The western North American population of monarchs west of the Rocky Mountains most often migrate to sites in California but have been found in overwintering Mexico sites.

Taxonomy[edit]

The name 'monarch' may be in honor of King William III of England.[6]

The monarch was originally named by Linnaeus in his Systema Naturae of 1758 and it was placed in the genus Papilio.[7] In 1780, Jan Krzysztof Kluk used the monarch as the type species for a new genus; Danaus.

The monarch is closely related to two very similar species that formed the Danaus (Danaus) subgenus before 2005. The first is the Jamaican monarch (D. cleophile) from Jamaica and Hispaniola. The second is the southern monarch (D. erippus), of South America south of the Amazon river. The southern monarch is almost indistinguishable from the monarch as an adult, though the pupae are somewhat different, and is often considered a subspecies of the monarch proper. But analysis of morphological, mtDNA 12S rRNA, cytochrome c oxidase subunit I, nuclear DNA 18S rRNA and EF1 subunit α sequence data by Smith et al. (2005) indicates it is better considered a distinct species. The separation of the monarch and southern monarch is comparatively recent. In all likelihood, the ancestors of the southern monarch separated from the monarch's population some 2 mya, at the end of the Pliocene. At the time, sea levels were higher and the entire Amazonas lowland was a vast expanse of brackish swamp that offered hardly any butterfly habitat.[8]

Following the review of Smith et al. (2005), two subspecies of the monarch are recognized:[8]

  • D. p. plexippus, the nominate subspecies, described by Linnaeus in 1758, is the migratory subspecies known from most of North America.
  • D. p. megalippe, named in 1826 by Jacob Hübner, is a nonmigratory subspecies, and is found from Florida and Georgia southwards, throughout the Caribbean and Central America to the Amazon River. Three local forms were at first considered other subspecies, but are actually colour varieties of D. p. megalippe:
    • D. p. m. forma leucogyne, named by Arthur G. Butler in 1884
    • D. p. m. forma portoricensis, named in 1941 by A.H. Clark
    • D. p. m. forma tobagi, also named in 1941 by A.H. Clark

Smith et al. did not take up Danaus plexippus nigrippus in their studies. According to Hay-Roe et al. (2007), this taxon is still recognised as a subspecies:[9]

Origin of name[edit]

Danaus (Greek Δαναός), a great-grandson of Zeus, was a mythical king in Egypt or Libya, who founded Argos; Plexippus was one of the 50 sons of Aegyptus, the twin brother of Danaus.

In Homeric Greek plexippos (πληξιππος) means "one who urges on horses", i.e. "rider or charioteer". In the 10th edition of Systema Naturae, at the bottom of page 467,[10] 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.[11][12]

Description[edit]

The monarch’s wingspan ranges from 8.9–10.2 cm (3½–4 in).[4] The upper side of the wings is tawny-orange, the veins and margins are black, and in the margins are two series of small white spots. The fore wings also have a few orange spots near the tip. The underside is similar, but the tip of the fore wing and hind wing are yellow-brown instead of tawny-orange and the white spots are larger.[13]

The male has a black patch of androconial scales on either hind wing (in some butterflies, these patches disperse pheromones, but are not known to do so in monarchs), and the black veins on its wing are narrower than the female’s. The male is also slightly larger.[13] One variation has been observed in Australia, New Zealand, Indonesia and the United States termed nivosus by lepidopterists. It is grayish-white in all areas of the wings that are normally orange and is only about 1% or less of all monarchs, but populations as high as 10% exist on Oahu in Hawaii, possibly due to selective predation.[14]

Like all insects, the monarch has six legs, but uses the four hindlegs as it carries its two front legs against its body.[15]

The eggs are creamy white and later turn pale yellow. They are elongated and subconical, with about 23 longitudinal ridges and many fine traverse lines.[13] A single egg weighs about 0.46 mg (0.0071 gr), and measures about 1.2 mm (47 mils) high and 0.9 mm (35 mils) wide.[16][17]

The caterpillar is banded with yellow, black, and white stripes. The head is also striped with yellow and black. Two pairs of black filaments are seen, one pair on each end of the body. The caterpillar reaches a length of 5 cm (2 in).[18]

The chrysalis is blue-green with a band of black and gold on the end of the abdomen. Other gold spots occur on the thorax, the wing bases, and the eyes.[19]

Range and distribution[edit]

Since the 19th century, it has been found in New Zealand, and in Australia.[20] It is resident in the Caribbean, Canary Islands, the Azores, and Madeira, Portugal, Spain[21] and is found as an occasional migrant in Western Europe and a rare migrant in the United Kingdom.[22] In North America, the monarch ranges from southern Canada to northern South America. It rarely strays to western Europe (rarely as far as Greece) from being transported by US ships or by flying there if weather and wind conditions are right. It has also been found in Bermuda, Cook Islands,[23] Hawaii, the Solomons, New Caledonia, New Zealand, Australia, New Guinea, Sri Lanka, India, Nepal, the Azores, and the Canary Islands.[19]

Migration[edit]

Monarch migration route
Overwintering monarchs cluster on oyamel trees in a preserve outside of Angangueo, Michoacan, Mexico; one tree is completely covered in butterflies.
Monarch Butterflies in Pacific Grove, California
Monarchs migrating during fall in central Texas

The eastern population migrates hundreds to thousands of miles to overwintering sites in Mexico. Southward migrations start in August and end at the first frost. There is a northward migration in the spring.[24] The eastern population migrates both north and south on an annual basis. But no individual makes the entire round trip. Female monarchs lay eggs for the next generation during these migrations.[25]

By the end of October, the population east of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve within the Trans-Mexican Volcanic Belt pine-oak forests in the Mexican states of Michoacán and México. The western population overwinters in various coastal sites in central and southern California, United States, notably in Pacific Grove, Santa Cruz, and Grover Beach.

The length of these journeys exceeds the normal lifespan of most monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a nonreproductive phase known as diapause, which may last seven months or more.[5] During diapause, butterflies fly to one of many overwintering sites. The overwintering generation generally does not reproduce until it leaves the overwintering site sometime in February and March.

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.

Migratory Theory Mechanisms[edit]

The North American Western and Eastern populations (D. plexippus) migrate to established overwintering spots each autumn. In one study monarchs released during the fall migration from Albuquerque, New Mexico were found overwintering in California and in Mexico.[26] The same study tested the ability of commercially bred monarchs (to the 9th generation) to migrate to overwintering areas.[26] Flight navigational patterns may be inherited, based on a combination of the position of the sun in the sky[27] and a time-compensated Sun compass that depends upon a circadian clock based in their antennae.[28][29] These populations may use the earth's magnetic field for orientation. The antennae contain cryptochrome, a photoreceptor protein sensitive to the violet-blue part of the light spectrum. In the presence of violet or blue light, it can function as a chemical compass.[30][31] Studies demonstrate that eastern and western populations do not use an internal ‘map’ to navigate to overwintering locations but instead are guided by a ‘compass’ that compels them to migrate in a southwest direction. This southwest directional migration is affected by large geographical features like the Rocky Mountains and The Gulf of Mexico.[32]

On June 24, 2014, scientists from the University of Massachusetts Medical School and Worcester Polytechnic Institute published the results of their study that confirms that monarch butterflies, like many birds and sea turtles, are aided by a geomagnetic compass[33] They also reported that it was proteins called CRY in the butterflies’ antennae that activate this inclination compass when light of a particular wavelength — the ultra-violet/blue end of the spectrum — fell on it.

New methods of studying the migration include the use of VHF transmitters and commercial aircraft.[34]

Global Migrations[edit]

Monarch butterflies can and have crossed the Atlantic. They are becoming more common in Bermuda and Spain, due to increased use of milkweed as an ornamental plant.[35] Monarch butterflies in Bermuda and Spain do not migrate. Butterflies sometimes appear in Great Britain. In Australia, monarchs make limited migrations in cooler areas,[36] On the islands of Hawaii, no migrations have been noted. The Southern Monarch, D. erippus migrates along the eastern edge of the Andean mountains in the autumn in Bolivia and Peru.[37]

One study examined wing colors of migrating monarchs using computer image analysis, and found migrants had darker orange (reddish-colored) wings than breeding monarchs.[38]

Habitat[edit]

The monarch is not limited to forest sanctuaries but can found in agricultural fields and pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides. The eastern North American overwinters in Mexican conifer groves.[39][40]

Adult food sources[edit]

Monarch butterfly feeding on nectar

Although larvae eat only milkweed, adult monarchs feed on the following nectar plants:

Males also take in 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.[40] Adult butterflies are also attracted to the liquids of foods we consume; they will drink mushy slices of bananas, oranges, and watermelon.

Reproduction[edit]

Monarch butterfly mating

The mating period for the overwinter population occurs in the spring, just prior to migration from the overwintering sites. The courtship is fairly simple and less dependent on chemical pheromones than other species in its genus.[41] Courtship is composed of two distinct stages, the aerial phase and the ground phase. During the aerial phase, the male pursues, nudges, and eventually takes down the female. Copulation occurs during the ground phase, where the male and female remain attached for about 30 to 60 minutes.[42] Only 30% of mating attempts end in copulation, suggesting that females have methods to avoid unwanted matings.[43] Differences in female ability to resist mating affect pairing patterns.[44] A spermatophore is transferred from the male to the female. Along with sperm, the spermatophore is thought to provide the female with energy resources to aid her in carrying out reproduction and remigration. The overwinter population returns only as far north as they need to go to find the early milkweed growth; in the case of the eastern butterflies, that is commonly southern Texas. The life cycle of a monarch includes a change of form called complete metamorphosis. The monarch goes through four radically different stages:

  1. The eggs are laid by the females during spring and summer breeding months onto the leaves of milkweed plants.[45]
  2. The eggs hatch (after four days), revealing worm-like larvae, the caterpillars. The caterpillars consume their egg cases, then feed on milkweed, and sequester substances called cardenolides, a type of cardiac glycoside. During the caterpillar stage, monarchs store energy in the form of fat and nutrients to carry them through the nonfeeding pupal stage. The caterpillar stage lasts around two weeks.
  3. In the pupa or chrysalis stage, the caterpillar spins a silk pad on a twig or leaf, and hangs from this pad by its last pair of prolegs. It hangs upside down in the shape of a 'J', and then molts, leaving itself encased in an articulated green exoskeleton. At this point, hormonal changes occur, leading to the development of a butterfly (metamorphosis). The chrysalis darkens (the exoskeleton becomes transparent) a day before it emerges, and its orange and black wings can be seen.
  4. The mature butterfly emerges after about two pupal weeks, and hangs from the split chrysalis for several hours until its wings are dry (often in the morning). Meanwhile, fluids are pumped into the crinkled wings until they become full and stiff. Some of this orangey fluid (called meconium) drips from the wings. Finally (usually in the afternoon), the monarch spreads its wings, quivers them to be sure they are stiff, and then flies away to feed on a variety of flowers, including milkweed flowers, red clover, and goldenrod.

Monarchs can live two to eight weeks in a garden having their host Asclepias plants and sufficient flowers for nectar.[46] This is especially true if the flower garden happens to be surrounded by native forests that lack flowers.

Sexual selection[edit]

Reproduction does not appear to be influenced by parasite levels. Instead it affected by size, fluctuating asymmetry, and wing condition of females.[citation needed] By the end of the mating season, larger females contain fewer spermatophores. Mating females are more asymmetric than non-mating females which plays a role in determining mate pairing.[citation needed] Females often resist male mating attempts. Studies suggest that damaged wings decrease mating in females.[44] Males who are fit are more likely to mate a greater proportion of days and are also more likely to achieve copulation. Both females and males typically mate more than once.[43] Spermatophore nutrients are absorbed and used in egg production. Females that mate several times laid more eggs than females who only mate once.[47]

Sperm competition[edit]

Male monarchs produce spermatophores, a sperm sac embedded in a gelatinous body, from accessory gland secretions.[48][49] Since male monarchs are highly polyandrous and females store sperm, there is need for sperm competition, selecting for males that gain sperm precedence. The spermatophore size of males increases with increasing time between matings, and larger spermatophores delay female re-mating. Therefore, by waiting to re-mate, males increase their sexual competitiveness, ultimately increasing the number of ova fertilized by their sperm.[47]

In addition, the production of large spermatophores could also benefit the females because spermatophore constituents may be used by females to affect the amount of offspring produced or the quality of offspring produced. By increasing female reproductive success, male reproductive success also increases. Studies have shown that the contents of Lepidopteran spermatophores are incorporated into the eggs and somatic tissue of females. Therefore, an increase in spermatophore size also increases the fecundity of female monarchs.[47] Sperm from males that produce larger spermatophores could also fertilize more female's eggs without increasing her lifetime reproductive success.[50]

Sperm precedence patterns were also observed, where second-male sperm precedence was more common than first or no-male sperm precedence. The advantage of second-male sperm suggests that the incoming sperm pushes back previously existing sperm, resulting in different layers of sperm from different males. However, second-male sperm precedence is rarely complete, suggesting that the sperm from the first male remains in the fertilization set, acting as a barrier to block sperm from other males.[50]

Pictorial lifecycle[edit]

Host plants[edit]

The host plants used by the monarch caterpillar include:

Americas:

African:

European:

Defense against predators[edit]

Swamp milkweed, one of many species of Asclepias milkweeds used by the monarch
Chemical structure of oleandrin, one of the cardiac glycosides

In both caterpillar and butterfly form, monarchs use a bright display of contrasting colors to warn potential predators of its undesirable taste and poisonous characteristics. This aposematic behavior is common among many insects, amphibians, and mammals alike. Additionally, monarchs are physically similar to the viceroy butterfly, exhibiting a classic case of mimicry.

Aposematism

Monarchs are foul-tasting and poisonous due to the presence of cardenolide aglycones in their bodies, which the caterpillars ingest as they feed on milkweed.[41] 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.[51] 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.[52]

Additional studies have shown that different species of milkweed have differing effects on growth, virulence, and transmission of parasites.[53] One specific species (Asclepias curassavica) appears to reduce the proportion of monarchs infected by parasites. There are two possible explanations for the positive role of A. curassavica on the monarch caterpillar. The first is that A. curassavica promotes overall monarch health to boost the monarch’s immune system. A second theory is that A. curassavica has a direct negative effect on the parasites.[53]

After the caterpillar becomes a butterfly, the toxin 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.[51] In order to combat predators that remove the wings only to ingest the abdomen, monarchs keep the most potent cardiac glycosides in their abdomens.[54]

Monarch toxins are pharmacologically similar to digitalis and produce extremely similar results in experimental settings.[51] In the wild, the toxins cause many birds to experience intense discomfort and vomiting. Many birds find monarchs unappetizing and quickly begin recognizing their distinct colors and avoiding them as food sources.

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.[55]

The monarch (left) and viceroy (right) butterflies exhibiting Müllerian mimicry

Human Interactions[edit]

Monarch male tagged with an identification sticker

The monarch is the state insect of Alabama,[56] Idaho,[57] Illinois,[58] Minnesota,[59] Texas,[60] Vermont,[61] and West Virginia.[62] It was nominated in 1990 as the national insect of the United States of America.[63] but the legislation did not pass.[64]

Monarchs can be attracted by cultivating a butterfly garden with specific milkweed species and nectar plants. Efforts are underway to establish these Monarch Waystations.[65] Monarchs are raised as a hobby and for educational purposes.[66][67] Butterfly farmers raise Monarchs and ship them to individuals and organizations to be released at a wedding or funeral, for example.[68] The release of captive bred Monarchs remains controverial.[69][70]

An IMAX film, Flight of the Butterflies, describes the story of the Urquharts, Brugger and Trail to then unknown migration to Mexican overwintering areas.[71]

Sanctuaries and reserves have been created at over-wintering locations in Mexico and California to limit habitat destruction. These sites can generate significant tourism revenue. [72]

Some organizations, such as the Cape May Bird Observatory, have monarch identification tagging programs. Plastic stickers are placed on the wing of the insect with identification information. Tracking information is used to study their migration patterns, including how far and where they fly.[73]

Threats[edit]

Predators[edit]

Although larva feed exclusively on milkweed, protective cardiac glycosides vary between species and parts of the host plant. Toxins in adult monarchs depend upon the amount consumed as larva. Not all monarchs are foul-tasting, but are Batesian or automimics. Some predators have learned to assess the toxins levels and avoid butterflies with high cardiac glycosides contents.

Overwintering monarchs in Mexico are preyed upon by Black-headed Grosbeaks, which are immune to toxin. The orioles and jays, have learned to eat the thoracic muscles and abdominal contents which contain lower toxin levels.[19] Some mice are able to withstand large doses of the toxin. 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.[39]

Cardiac glycosides levels are higher in the abdomen and wings. Some predators can differentiate betwwen these parts and consume only the most palatable ones.[74] Bird predators include brown thrashers, grackles, robins, cardinals, sparrows, scrub jays and pinyon jays.[74]

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).[75] The Chinese mantid ("Tenodera sinensis") will open the integument to allow the gut to fall out. Once the gut is removed, they will consume the rest of the body. Caterpillars contain higher levels of cardenolides in their guts than in the rest of their bodies. [76]

Several birds have also adapted various methods that allow them to ingest monarchs without experiencing the ill effects associated with the cardiac glycosides. 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.[77] The grosbeak, on the other hand, has adapted the ability an insensitivity to secondary plant poisons which 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 of predation effectively reduces the potential predation of monarchs by 50 percent and indicates that monarch aposematism has a legitimate purpose.[77]

White morph of the monarch in Hawaii called White Monarch.

On Oahu, a white morph of the monarch has emerged. This is because of the introduction, in 1965 and 1966, of two bulbul species, Pycnonotus cafer and Pycnonotus jocosus. They are now the most common insectivore birds, and probably the only ones preying on insects as large as the monarch. Monarchs in Hawaii are known to have low cardiac glycoside levels, but the birds may also be tolerant of the chemical. 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 colour, 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.[78]

Parasites[edit]

Parasites include the tachinid flies Sturmia convergens[79] and Lespesia archippivora. Lesperia-parasitized butterfly larvae complete the formation of their crysalid but die before they emerge as an adult. Before pupation is complete, one white maggot comes out of the chrysalid. The maggot forms a brown pupa on the ground then emerges as an adult.[80]

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 after. 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.[80]

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 probably occur at low frequencies in nature. This is not the case in laboratory or commercial rearing, where after a few generations, all individuals can be infected.[81]

Confusion of host plants[edit]

The black swallow-wort is problematic for monarchs in North America. Monarchs lay their eggs on these relatives of native milkweeds because they produce stimuli similar to milkweed. Once the eggs hatch, the caterpillars are poisoned by the toxicity of this invasive plant from Europe.[citation needed]

Population decline[edit]

The yearly decrease in the monarch butterfly population has been linked to the decrease in the milkweed plant (Asclepias)—a primary food for monarchs—from herbicide use in the butterfly’s reproductive and feeding areas. The destruction of common milkweed has effectively eliminated the food source from most of the habitat monarchs used to use.[82] Common milkweed is susceptible to the use of herbicides. Varietals do exist, however, (see Human Interactions) that can be successfully planted in gardens and other areas to help mitigate habitat loss in the wild.[83]

Genetically Modified Crops[edit]

Conservationists attribute the disappearance of mikweed spieces to monolithic agricultural practices in the Midwest, where genetically modified seeds are bred to resist herbicides that eliminate milkweed nearby. Growers eliminate milkweed that previously grew between the rows of food crops. Corn and soybeans are resistant to the effect of the herbicide glyphosate. The increased use of these crop strains is correlated with the decline in Monarch populations between 1999 and 2010.[84][85] Chip Taylor, director of Monarch Watch at the University of Kansas, said the Midwest milkweed habitat "is virtually gone" with 120–150 million acres lost.[86][87]

A letter published in Nature proposed that pollen from genetically modified maize could deposit onto larval food plants, Asclepias spp. (milkweed), increasing mortality of the larva.[88]

Loss of Overwintering Habitat[edit]

The area of forest occupied by overwintering monarch butterflies in Mexico reached its lowest level in two decades in 2013. According to a survey carried out during the 2012–2013 winter season by the WWF-Telcel Alliance, and Mexico’s National Commission of Protected Areas (CONAP), the nine hibernating colonies occupy a total area of 2.94 acres of forest—representing a 59% decrease from the 2011–2012 survey of 7.14 acres.[citation needed]

The same survey in 2012-2013 showed the decline is continuing. There were only seven colonies occupying 0.67 hectares (1.66 acres), the third consecutive record low since record-keeping began in 1995-1996. It represents a 44% decrease from the previous year, a 76% decrease from 2011-2012 and a 92% decrease compared to the 1996-1997 count.

Mexican environmental authorites continue to monitor illegal logging of the [Oyamel trees]. The Oyamel is a major spieces of evergreen on which the overwintering butterflies spend a significant time during their winter diapause.[89]

Climate[edit]

Climate variations during the fall and summer affect butterfly reproduction. Rainfall, and freezing temperatures affect milkweed growth and the survival of migrating adult butterflies.[citation needed]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 95°F can be lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate.” [90] [91]

Concerned individuals governmental agencies, and organizations have made efforts to restore milkweed habitats to provide nectar and foodplants.[92][93][94][95]

Genome[edit]

A 273-million base pair draft sequence of the monarch butterfly genome was published in 2011, including a set of 16,866 protein-coding genes. Comparison to the sequence of the silk moth Bombyx mori reveals the Lepidoptera as a relatively fast-evolving order. The monarch genome provides a number of insights into the butterfly's migratory behaviour, including the molecular underpinnings of the circadian clock and juvenile hormone pathway, as well as a suite of microRNAs that are differentially expressed between summer and migratory monarchs.[96][97][98]

Conservation[edit]

Conservationists are lobbying transportation departments and utilities to reduce their use of herbicides and specifically encourage milkweed to grow along roadways and power lines. The goal is to reduce roadside mowing and application of herbicides during the butterfly breeding season. Environmental conservationists are lobbying large-scale agriculture companies to leave small areas of cropland unsprayed to allow the butterflies to breed.[85]

See also[edit]

References[edit]

  1. ^ Committee On Generic Nomenclature, Royal Entomological Society of London; Of Entomology, British Museum (Natural History) Dept (2007-05-23) [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. Retrieved 2008-06-04. 
  2. ^ 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 0-665-26322-8. Retrieved 2008-06-04. 
  3. ^ "Monarch Butterfly". Retrieved March 26, 2014. 
  4. ^ a b Garber, Steven D. (1998). The Urban Naturalist. Courier Dover Publications. pp. 76–79. ISBN 0-486-40399-8. Retrieved 2008-05-26. 
  5. ^ a b "Monarch, Danaus plexippus". Retrieved 2008-08-27. 
  6. ^ Adams, Jean Ruth (1992). Insect Potpourri: Adventures in Entomology. CRC Press. pp. 28–29. ISBN 1-877743-09-7. Retrieved 2008-05-21. 
  7. ^ Linnaeus, Carl (1758). Systema Naturae (in Latin) 1. Stockholm: Laurentius Salvius. p. 471. OCLC 174638949. Retrieved 2012-06-05. 
  8. ^ a b Smith, David A.; Gugs Lushai and John A. Allen (June 2005). "A classification of Danaus butterflies (Lepidoptera: Nymphalidae) based upon data from morphology and DNA" (PDF). Zoological Journal of the Linnean Society 144 (2): 191–212. doi:10.1111/j.1096-3642.2005.00169.x. Retrieved 2008-05-19. 
  9. ^ Hay-Roe, Miriam M. et al. (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: 445–453.
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  11. ^ 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 colourful 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." (= The names of the Danai candidi have been derived from the daughters of Danaus, those of the Danai festivi from the sons of Aegyptus).
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