Monarch Butterflies Migrate 3,000 Miles—Here's How
The colorful insect's migration across the North American continent is one of the greatest natural events on Earth.
Each fall, millions of monarch butterflies leave their summer breeding grounds in the northeastern U.S. and Canada and travel upwards of 3,000 miles to reach overwintering grounds in southwestern Mexico.
But unlike birds or wildebeest that also embark on epic migrations, these individual butterflies will never return. (See National Geographic's amazing photos of monarchs.)
Why won't they make it all the way back? How do they know where to go in the first place?
As the days get shorter and the temperatures drop off, monarchs begin to abandon breeding and feeding territories in search of a safe place to spend the winter.
For monarchs, that overwintering ground is found high up on just a few mountains in central Mexico. Once there,
