Which butterfly species migrates between Mexico and Canada each year?

The monarch butterfly is the species famous for migrating between Mexico and Canada each year.

Eastern North American monarchs travel south in autumn to overwinter in central Mexico, where millions may cluster on oyamel fir trees. In spring, they begin moving north again, laying eggs on milkweed along the route. No single monarch usually completes the entire round trip: several generations are involved on the northward journey, while the special overwintering generation can live for many months.

Monarchs are often confused with viceroy butterflies because the two have orange wings and black veins. Their ranges overlap, but they are different species and have different caterpillar food plants. Western North American monarchs generally overwinter along the California coast rather than in Mexico. The migration is threatened by habitat loss, reduced milkweed, pesticides, and changing climate conditions.