Millions of butterflies begin their annual migration ahead of winter

The winding down of summer marks the start of the annual migration of millions of monarch butterflies across North America.

According to the U.S. Fish and Wildlife Service , the migration typically runs from mid-August through mid-November, when butterflies leave their summer breeding grounds and begin a trek that spans thousands of miles.

Monarchs generally west of the Rocky Mountains head to California and Mexico’s Baja California, while those east of the Rockies travel to forests in the heart of Mexico.

Biologists say that unlike most insects, which attempt to escape the cold by hibernating and finding refuge, monarch butterflies cannot survive prolonged cold conditions.

Monarchs are able to survive the 3,000-mile trek by nectaring on late-blooming plants along the way, such as gold