A 500 Million Strong Butterfly Migration
The Monarch Butterfly is not able to survive the cold winters of most of the United States and Canada so they migrate south and west each autumn to escape the cold winter. Over 500 million Monarch Butterflies begin this migration as early as August every year. Monarchs west of the Rockies will migrate and hibernate in and around Pacific Grove, California. Monarchs east of the Rockies will try to follow the prevailing winds south into Mexico, crossing the Texas border and following the Sierra Madre Oriental mountains to their wintering grounds. This migration is the longest and greatest insect migration on Earth as they will travel up to 2,500 miles in their journey. Only one of five will survive, but their numbers are so vast that over 100 million will complete the journey to their wintering grounds of central Mexico. There they will winter in the same forests as their great grandparents did the year before, a perfect combination of trees, food, and temperature at over ten thousand feet to feed and breed before beginning their return trip north the following spring. Monarch Butterflies only have a life span of about two months, so it is the fourth generation that return every year. How they know how to migrate to the same place they have never been every year is still unknown.
The following two pictures are of overwintering Monarch Butterflies clustering on Oyamel trees in a preserve outside of Angangueo, Michoacan, Mexico.
Monarch Butterflies in flight in Central Mexico
Monarch Butterflies wintering in Pacific Grove, California.