10/14/2026
The Epic Journey: Eastern North American monarchs make a multi-thousand-mile trek starting around September, often arriving in Michoacán and the State of Mexico around early November.
A Multi-Generational Relay: The butterflies that fly south to Mexico are actually the "super generation" (the fourth generation). Their great-great-grandparents started the journey north in the spring, meaning these travelers find their way to wintering grounds they have never seen before.
Winter Roosting: Once they arrive, millions of monarchs cluster tightly together on fir and pine trees in high-altitude sanctuaries like the Monarch Butterfly Biosphere Reserve to conserve energy until spring.