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The Monarch butterfly (Danaus plexippus) is probably the best known North
American butterfly. Its wings have an orange and black pattern. The females have
darker veins on their wings and the males have a spot in the center of each hind
wing from which pheromones (chemical attractants) are released.
 Monarchs
are famous 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 over winters in
Michoacán, Mexico and the western population over winters in various sites in
central coastal California, United States, primarily in Pacific Grove and Santa
Cruz. These journeys last longer then any given butterfly lives (lives 4
days as egg, 2 weeks as caterpillar, 10 days as chrysalis, and 2-6 weeks as a
butterfly). How the Monarch butterfly manages to return to the same over
wintering spots over the life of several generations remains a mystery. This is
one of the few insects that is able to cross the Atlantic ocean. A few Monarchs
turn up in the far southwest of Great Britain in years when the wind conditions
are right.
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