Filo: Arthropoda
Clase: Insecta
Orden: Lepidoptera
Familia: Nymphalidae
Subfamilia: Danainae
Tribu: Danaini
Subtribu: Danaina
Género: Danaus -Kluk, 1802
Especie: D. plexippus
Nombre binomial: Danaus plexippus - Linnaeus, 1758
Common name: Monarch
Description: The Monarch’s wingspan ranges from 8.9–10.2 cm (3½–4 in.). 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.
The male has a black patch of androconial scales responsible for dispersing pheromones on the hind wings, and the black veins on its wing are narrower than the female’s. The male is also slightly larger.
A color variation has been observed in Australia, New Zealand, Indonesia and the United States as early as the late 19th century. Named nivosus by Lepidopterists, it is grayish white in all areas of the wings that are normally orange. Generally it is only about 1% or less of all monarchs, but has maintained populations as high as 10% on Oahu in Hawaii, possibly due to selective predation.
Like all insects the Monarch has six legs, however it uses only four of its legs as it carries its two front legs against its body.
The eggs are creamy white and later turn pale yellow. They are elongate and subconical, with approximately 23 longitudinal ridges and many fine traverse lines.[13] A single egg weighs about 0.46 milligrams (0.0071 gr), and measures about 1.2 millimetres (47 mils) high and 0.9 millimetres (35 mils) wide.
The caterpillar is banded with yellow, black, and white stripes. The head is also striped with yellow and black. There are two pairs of black filaments, one pair on each end of the body. The caterpillar will reach a length of 5 cm (2 in).
The chrysalis is blue-green with a band of black and gold on the end of the abdomen. There are other gold spots on the thorax, the wing bases, and the eyes.
Distribution: 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 U. S. ships or by flying there if weather and wind conditions are right. It has also been found in Bermuda, Hawaii, the Solomons, New Caledonia, New Zealand, Australia, New Guinea, Ceylon, India, the Azores, and the Canary Islands.
Migration: Monarchs are especially noted for their lengthy annual migration. In North America they make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. The monarch is the only butterfly that migrates both north and south as the birds do on a regular basis. But no single individual makes the entire round trip. Female monarchs deposit eggs for the next generation during these migrations.
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 sites in central coastal and southern 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 seven months or more. 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 of those east of the Rockies 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 the position of the sun in the sky and a time-compensated Sun compass that depends upon a circadian clock that is based in their antennae. New research has also shown that Monarch butterflies can use the earth's magnetic field for orientation. The antennae contain cryptochrome a photoreceptor protein that is sensitive to the violet-blue part of the spectrum. In the presence of violet or blue light it can function as a chemical compass, which tells the animal if it is aligned with the earths magnetic field, but it is unable to tell the difference between the magnetic North or South. The complete magnetical sense is present in a single antenna.
Monarch butterflies are one of the few insects capable of making trans-Atlantic 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. In Australia, Monarchs make limited migrations in cooler areas, but the Blue Tiger butterfly is better known in Australia for its lengthy migration. Monarchs can also be found in New Zealand. On the islands of Hawaii no migrations have been noted.
Monarch butterflies are poisonous or distasteful to birds and mammals because of the presence of cardiac glycosides that are contained in milkweed consumed by the larva. It is thought that the bright colors of larvae and adults function as warning colors. During hibernation monarch butterflies sometimes suffer losses because hungry birds pick through them looking for the butterflies with the least amount of poison, but in the process killing those that they reject.
A recent study examined wing colors of migrating monarchs using computer image analysis and found migrants had darker orange (reddish colored) wings than breeding monarch.
