Monarch

Danaus plexippus

Summary 5

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. Its wings feature an easily recognizable orange and black pattern, with a wingspan of 8.9–10.2 cm (3½–4 in).

Description 6

Commonly and easily mistaken for the similar viceroy butterfly, the monarch’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 in the margins are two series of small white spots. 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.

Monarch flight has been described as "slow and sailing". However, startled monarchs often fly quickly.

Adults exhibit sexual dimorphism. Males are slightly larger than females and have a black patch or spot of androconial scales on each hindwing (in some butterflies, these patches disperse pheromones, but are not known to do so in monarchs). The male's black veins on his wings are lighter and narrower than those of females.

One variation, the "white monarch", observed in Australia, New Zealand, Indonesia and the United States, is called nivosus by lepidopterists. It is grayish-white in all areas of its 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.

The monarch has six legs like all insects, but uses its middle legs and hindlegs as it carries its two forelegs against its body.

Larva and Chrysalis Description 7

The caterpillar goes through five major, distinct stages of growth and after each one, it molts. Each caterpillar, or instar, that molts is larger than the previous as it eats and stores energy in the form of fat and nutrients to carry it through the nonfeeding pupal stage.

The first instar caterpillar that emerges out of the egg is pale green and translucent. It lacks banding coloration or tentacles. The larvae or caterpillar eats its egg case and begins to feed on milkweed. It is during this stage of growth that the caterpillar begins to sequester cardenolides. The circular motion a caterpillar uses while eating milkweed prevents the flow of latex that could entrap it.

The second instar larva develops a characteristic pattern of white, yellow and black transverse bands. It is no longer translucent but is covered in short setae. Pairs of black tentacles (stinkhorns) begin to grow. One pair grows on the thorax and another pair on the abdomen.

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. These third stage caterpillars began to eat along the leaf edges.

The fourth instar has a different banding pattern. It develops white spots on the prolegs near the back of the caterpillar.

The fifth instar larva has a more complex banding pattern and white dots on the prolegs, with front legs that are small and very close to the head.

At this stage of development, it is relatively large compared to the earlier instars. The caterpillar completes its growth. At this point, it is 25 to 45 mm long and 5 to 8 mm wide. This can be compared to the first instar, which was 2 to 6 mm long and 0.5 to 1.5 mm wide. Fifth instar larvae increase 2000 times from first instars. Fifth-stage instar larva chew through the petiole or mid-rev of milkweed leaves and stop the flow of latex. After this, they eat more leaf tissue. Before pupation, larva must consume milkweed to increase their mass. Larva stop feeding and search for a pupation site. The caterpillar attaches itself securely to a horizontal surface, using a silk pad. At this point, it latches on with its hind legs and hangs down. It then molts into an opaque, blue-green chrysalis with small gold dots. At normal summer temperatures, it matures in a few weeks. The cuticle of the chrysalis becomes transparent and the monarch's characteristic orange and black wings become visible. At the end of metamorphosis, the adult emerges from the chrysalis, expands and dries its wings and flies away. Monarch metamorphosis from egg to adult occurs during the warm summer temperatures in as little as 25 days, extending to as many as seven weeks during cool spring conditions. During the development, both larva and their milkweed hosts are vulnerable to weather extremes, predators, parasites and diseases; commonly fewer than 10% of monarch eggs and caterpillars survive.

Larval host plants 6

The host plants used by the monarch caterpillar include:

Asclepias curassavica has been planted as an ornamental and naturalized. Its distribution is probably worldwide. Year-round plantings may be the cause of new overwintering sites along the Gulf coast and in Spain. Needs Citation. Species of Asclepias in Floirda are also hosts for the Monarch.

GTM Occurrence 8

The Monarch is considered frequent in abundance. Most sightings are in the open habitat of Transect A, with 2 sightings along the Glasswort Loop (Transect C). It occurs from April to December with peak abundance in October. There have been 45 specimens observed as of December 28, 2015.

Distribution 7

The range of the western and eastern populations of the monarch butterfly expands and contracts depending upon the season. The range differs between breeding areas, migration routes, and winter roosts.

In North America, 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, New Guinea, Sri Lanka, India, Nepal, the Azores, the Canary Islands, South Africa, Gibraltar, Philippines, North Africa and Honolulu. It appears in the UK in some years as an accidental migrant. No genetic differences between monarch populations exist. Reproductive isolation has not created subspecies.

Habitat 6

Overwintering populations of D. plexippus are found in Mexico, California, along the Gulf coast, year-round in Florida, and in Arizona where the habitat has the specific conditions necessary for their survival. Their overwintering 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. Habitat restoration is a primary goal in monarch conservation efforts. Habitat requirements change during migration. During the fall migration, butterflies must have access to nectar-producing plants. During the spring migration, butterflies must have access to larval food plants and nectar plants.

Migration 6

In the U.S., the eastern population migrates both north and south on an annual basis. The population east of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve in Mexico. The western population overwinters 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. Commercially bred monarchs migrate to overwintering sites in Mexico adding to already existing data of migratory behavior. Not all monarchs in the eastern population migrate to Mexico.

Nature serve conservation status 9

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.

Sources and Credits

  1. (c) TexasEagle, some rights reserved (CC BY-NC), http://www.flickr.com/photos/10789832@N00/2972095940
  2. (c) Martin LaBar, some rights reserved (CC BY-NC), https://www.flickr.com/photos/martinlabar/254075049/
  3. (c) Jônatas Cunha, some rights reserved (CC BY-SA), https://www.flickr.com/photos/jonycunha/4081050561/
  4. (c) gailhampshire, some rights reserved (CC BY), https://www.flickr.com/photos/gails_pictures/6783335077/
  5. Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Danaus_plexippus
  6. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Monarch_butterfly
  7. Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Monarch_butterfly
  8. (c) GTMResearchReserve, some rights reserved (CC BY-SA)
  9. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28797771

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