Monarch butterfly migration

Monarch butterfly migration is the phenomenon, mainly across North America, where the monarch subspecies Danaus plexippus plexippus migrates each autumn to overwintering sites near the west coast of California or mountainous sites in central Mexico. Other populations from around the world perform minor migrations or none at all. This massive movement of butterflies has been recognized as "one of the most spectacular natural phenomena in the world".

The North American monarchs begin their southern migration in September and October. Migratory monarchs originate in southern Canada and the northern United States. They then travel thousands of kilometers to overwintering sites in central Mexico. The butterflies arrive at their roosting sites in November. They remain in roosts atop volcanic mountains on oyamel fir trees (Abies religiosa) during the winter months and then begin their northern migration in March, back to North America and southern Canada.

Two to three generations of monarchs complete the migration north. Female monarchs lay eggs for a subsequent generation during the northward migration. Four generations are involved in the annual cycle. The generation undertaking the southbound migration lives eight times longer than their parents and grandparents due to a regulatory age-inducing hormone. Similarly, the western populations migrate annually from regions west of the Rocky Mountains to overwintering sites near the coast of California.

Not all monarch populations make major migrations. Monarchs migrate short distances in Australia and New Zealand. There are some populations of D. p. plexippus, such as in Florida and the Caribbean, as well as another subspecies (D. p. megalippe) distributed in the Caribbean, Central America and northern South America, that do not migrate. Additional overwintering sites have been identified in Arizona and northern Florida. In encouraging news, the eastern monarch butterfly population nearly doubled in 2025, according to a report announced in Mexico. The population wintering in central Mexico's forests occupied 4.42 acres (1.8 ha), up from 2.22 acres (0.9 ha) during the previous winter. While monarchs occupied nearly twice as much forest habitat as they did during the previous year, populations remained far below the long-term average.