The monarch butterfly is one of the most familiar North American butterflies and is considered an iconic pollinator species. Its wings feature an easily recognizable black, orange and white pattern. The viceroy butterfly is similar in color and pattern, but is markedly smaller and has an extra black stripe across each hind wing.
The eastern North American monarch population is notable for its annual southward late-summer/autumn migration from the United States and southern Canada to Mexico. During the fall migration, monarchs cover thousands of miles, with a corresponding multigenerational return north. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in California, but they have been found in overwintering Mexican sites as well.
Monarch butterflies are not able to survive the cold winters of most of the United States so they migrate south and west each autumn to escape the cold weather. Also, the larval food plants do not grow in their winter overwintering sites, so the spring generation must fly back north to places where the plants are plentiful. The monarch migration usually starts in October, but can start earlier if the weather turns cold sooner than expected.
The monarch butterflies will spend their winter hibernation in Mexico and some parts of Southern California where it is warm all year long. If the monarch lives east of the Rocky Mountains, it will usually migrate to Mexico and hibernate in oyamel fir trees (photo courtesy U.S. Fish and Wildlife Service). If the monarch butterfly lives west of the Rocky Mountains, then it usually hibernates in and around Pacific Grove, Calif., in eucalyptus trees.
Monarch butterflies use the very same trees each and every year when they migrate, which seems odd because they aren’t the same butterflies that were there last year. Monarch butterflies are the only insect that migrates to a warmer climate that is 2,500 miles away each year.