Monarch butterfly
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[Photo] Photograph of the Monarch Butterfly (Danaus plexippus) on a Purple Coneflower (Echinacea purpurea). Photo taken at the Tyler Arboretum. Date Saturday, July 28, 2007. Author Photo by and (c)2007 Derek Ramsey (http://en.wikipedia.org/wiki/User:Ram-Man)

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 Mexico, Azores, Portugal and Spain. Its wings feature an easily recognizable orange and black pattern, with a wingspan of 8.5???12.5 cm (3.34 in???4.92in). (The Viceroy Butterfly has a similar size, color, and pattern, but can be distinguished by an extra black stripe across the hindwing.) Female monarchs have darker veins on their wings, and the males have a spot in the center of each hindwing from which pheromones are released.

Migration
Monarchs are especially noted for their lengthy annual migration. They make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. Female Monarchs deposit eggs for the next generation during these migrations. By the end of October, the population of the Rocky Mountains migrates to the sanctuaries in the area of Angangueo, Ocampo, Zit??cuaro and El Rosario in Michoac??n, Mexico. 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 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 non-reproductive phase known as diapause and may live up to 7 months. During diapause, butterflies fly to one of many overwintering sites. The generation that overwinters generally does not reproduce until it leaves the overwintering site sometime in February and March. It is thought that the overwinter population may reach as far north as Texas and Oklahoma during the spring migration. It is the second, third and fourth generations that return to their northern locations in the United States and Canada 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 appear to be inherited, based on a combination of circadian rhythm and the position of the sun in the sky.

Monarch butterflies are one of the few insects capable of making transatlantic crossings. They are becoming more common in Bermuda due to increased usage of milkweed as an ornamental plant in flower gardens. Monarch butterflies born in Bermuda remain year round due to the island's mild climate.

A few Monarchs turn up in the far southwest of Great Britain in years when the wind conditions are right, and have been sighted as far east as Long Bennington. 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.

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 the 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. 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, a type of cardiac glycosides. 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.

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http://en.wikipedia.org/wiki/Monarch_butterfly

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