The Monarch Butterfly, Danaus plexippus
The Monarch is the most recognized butterfly in North America. The dorsal wing surface is orange with black borders and veins. The ventral wing surface is similar, but paler. The head, thorax, and wing borders and tips are covered in white spots. Compared to females, males may be brighter orange and usually have thinner, better defined wing veins. Males also have two black dots, one on the dorsal surface of each hindwing (as in the individual pictured above). The female lacks these dots, which the male uses as a “scent patch” to release a pheromone when mating. Adult wing span measures 8 – 12 cm.
Monarchs range from southern Canada down throughout the entire United States, Central America, and most of South America. They also occur in Australia, Hawaii, and other Pacific islands. Adults from northern areas make massive migrations south every August – October to hibernate in either Mexico (if east of the Rocky Mountains) or along the California coast (if west of the Rocky Mountians). In Mexico, Monarchs roost together in trees, forming aggregations of possibly millions of adults. Adults from tropical regions do not migrate.
Adults can be found in open areas, such as fields, meadows, along roads, and marshes, often basking with their wings open. Adults feed on nectar from a variety of wild flowers. Females lay single eggs on the underside of milkweed leaves.
Monarch caterpillars are striped white, black, and yellow, and feed solely on the leaves of milkweed. Both caterpillars and adults store milkweed poisons in their body tissues. These poisons make them distasteful, and predators associate the Monarch’s bright, warning colours with a poisonous meal. The caterpillars eventually pupate in a yellowish-green chrysalis.