Which insect migrates from North America to Mexico each fall?

The monarch butterfly migrates from North America to Mexico each fall. Most monarchs east of the Rocky Mountains travel south from southern Canada and the northern United States to wintering forests in central Mexico.

The migration usually begins in late summer and early autumn, with large numbers reaching Mexico in November. There they gather in mountain sanctuaries, often clustering on oyamel fir trees in the states of Michoacán and México. The butterflies remain there through winter before beginning the northward journey in spring.

This migration is unusual because no single butterfly completes the entire annual cycle in both directions. The northward return takes two to three generations, with females laying eggs along the route on milkweed plants. The fall migrants are a special long-lived generation that can survive for many months instead of the few weeks typical of summer monarchs.

The western North American population follows a different pattern: many of those butterflies overwinter along the California coast rather than in Mexico. Resident monarch populations in places such as Florida and the Caribbean may not undertake the same long-distance migration.