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The Monarch butterfly
(Danaus plexippus) is a well-known North American butterfly. Its
wings feature an easily recognizable orange and black pattern.
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. In profileMonarchs 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 Monarch butterflies deposit eggs for the next generation
during these migrations. The population east of the Rocky Mountains
overwinters in Michoacán, Mexico, and the western population
overwinters in various sites in central coastal California, notably
in Pacific Grove and Santa Cruz. The length of these journeys
far exceeds the lifetime of any given butterfly.
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How the species
manages to return to the same overwintering spots over a gap of
several generations remains a mystery. This is one of the few
insects to manage transatlantic crossings. A few Monarchs turn
up in the far southwest of Great Britain in any year when the
wind conditions are right. The life cycle of a Monarch butterfly
includes a change of form called complete metamorphosis. This
process goes through four radically different stages. First, as
mentioned above, the eggs are laid by the females during migration.
Second, 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. The amount accumulated depends on the level
present in the milkweed. .
Images 1 Though 6 Are From The U.S. Fish & Wildlife Service
Images 7 Through 12 Are From The U.S.D.A.
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