Monarch butterfly
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| Danaus plexippus (Linnaeus, 1758) |
The Monarch butterfly (Danaus plexippus) is a well-known North American butterfly. Since the 19th century, it is also found in New Zealand, and in Australia where it is also known as the Wanderer Butterfly. In Europe it is resident in the Canary Islands (except Lanzarote) and Madeira, and is found as a migrant in the Azores, Portugal and Spain. Its wings feature an easily recognisable orange and black pattern, with a wingspan of 8.5–12.5 cm. The females have darker veins on their wings, and the males have a spot in the center of each hindwing from which pheromones are released.
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[edit] Migration
Monarchs are especially noted for their lengthy annual migration. They make massive southward migrations from August through October. A northward migration takes place in the spring. Female Monarchs deposit eggs for the next generation during these migrations. The population east of the Rocky Mountains overwinters in the sanctuary in Angangueo, Michoacán, Mexico, and the western population overwinters in various sites in central coastal California, United States, notably in Pacific Grove and Santa Cruz. The length of these journeys far exceeds the lifetime of most Monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer lives up to 7 months, during which it flies to the overwinter location. This generation does not reproduce until it leaves the overwinter location the following spring, but it is actually this generation's children and great-grandchildren that return to their northern location in the spring. How the species manages to return to the same overwintering spots over a gap of several generations is still a subject of research; the flight patterns are inherited, based on a combination of circadian rhythm and the position of the sun on the sky.[1]
A recent study suggests that butterflies have special ultraviolet photoreceptors that provide them with a sense of direction.[2] This is one of the few insects to manage transatlantic crossings. Once very common in Bermuda, they are becoming endangered due to the loss of milkweed, eradicated as a weed. A few Monarchs turn up in the far southwest of Great Britain in years when the wind conditions are right. Monarchs can also be found in New Zealand during summer, but are absent the rest of the year.
On the island of Hawaii no migrations have been noted. Monarchs can live a life of six to eight weeks in a garden having their host asclepias plants and sufficient flowers for nectar. This is especially true if the flower garden happens to be surrounded by native forest that seems to be lacking in flowers.
[edit] Metamorphosis
The life cycle of a Monarch includes a change of form called complete metamorphosis. The Monarch goes through four radically different stages:
- The eggs are laid by the females during spring and summer breeding months.
- The eggs hatch, revealing worm-like larva, the caterpillars. The caterpillars consume their egg cases, then feed on milkweed, and sequester substances called cardenolides, related to the cardiac glycoside digitalis. During the caterpillar stage, Monarchs store energy in the form of fat and nutrients to carry them through the non-feeding pupa stage.
- In the pupa or chrysalis stage, the caterpillar spins a silk pad on a twig, leaf, etc. 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.
- The mature butterfly emerges after about two weeks and feeds on a variety of flowers, including milkweed flowers, red clover, and goldenrod.
 Monarch butterfly laying eggs |
 Monarch eggs on Swan Plant |
 Monarch caterpillars |
 Monarch caterpillar begining pupation |
 Monarch butterfly chrysalis |
 Emerging from chrysalis |
[edit] Reproduction
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 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. 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.
Once they reach their breeding grounds, the females lay their eggs on milkweed host plants. The egg and larval period is temperature dependent and lasts about 2 weeks. At the end of this period, the larva enter a period of pupation as a chrysalis for 9 to 15 days, after which an adult butterfly emerges to continue the next step of the annual migration. On some remote islands, the monarch never migrates but remains in the garden where it was "born".
[edit] Defense against predators
Monarchs are foul-tasting and poisonous due to the presence of cardenolides in their bodies, which the caterpillars ingest as they feed on milkweed. Both forms advertise their unpalatability with bright colors and areas of high contrast on the skin or wings. This phenomenon is known as aposematism.
Monarchs share this defense with the even more unpleasant-tasting and similar-appearing Viceroy butterfly, in an example of Müllerian mimicry. (Viceroys were at one time believed to be Batesian mimics of Monarchs.)
[edit] Popularity
The Monarch is the state insect of Alabama, Idaho, Illinois, and Texas, and the state butterfly of Minnesota and West Virginia. It was nominated in 1989 as the national insect of the United States, and is the national insect of Canada. The Monarch's name and color were also the inspiration for the name and home strip of the Michoacán-based CA Monarcas Morelia professional football team.
Many people like to attract Monarchs by making a butterfly garden, and other people like to raise them for pleasure or for educational purposes.
[edit] Threats
Recent illegal deforestation of the Monarch's overwintering grounds have led to a drastic reduction in the butterfly's population. Efforts to classify it as a protected species and to restore its habitat are under way. Mexican authorities expected a significant increase in the Monarch population in the 2005-2006 season.
Monarch butterflies are susceptible to Ophryocystis elektroscirrha, a protazoan which parasitizes them. It is present on the abdomen of adult butterflies and passed to their offspring when the spores rub off during egg-laying and are then ingested by the caterpillars. The effects of the parasite on Monarchs include decreased weight, shortened lifespan, weakened wings, rapid weightloss, or inability to close, though this varies between butterfly populations and parasite strains [3].
[edit] Popular culture
The Monarch is a supervillain from the Adult Swim cartoon The Venture Bros. He claims to have been raised by Monarch butterflies after surviving a plane crash that killed his parents, although his mannerisms and personality demonstrate almost no knowledge of their biology or behavior.
A monarch butterfly appeared in the SpongeBob SquarePants episode, Wormy.
An episode of Malcolm in the Middle simply entitled "Butterflies" has a plot with Reese raising hundreds of Monarch caterpillars. Eventually, they all become adult butterflies which flock Reese's room and begin to cover up Reese, to his horror. Real caterpillars and butterflies were used, though the enormous fluttering flock near the end was done with computer-generated imagery.
[edit] References
[edit] External links
- Reference quality macro photographs: Monarch adult, larvae and chrysalis
- Live Monarch Foundation
- Monarch Watch of the University of Kansas Entomology Department
- Incredible Journey Over Lake Erie from Parks Canada
- Michoacan Reforestation Fund
- Monarch Monitoring 2005 on the Eastern Shore of Virginia
- USGS description of Monarch butterfly
- Monarch butterfly pictures (Danaus plexippus)
- MonarchHealth!
- Monarch Butterfly Trust NZ
