The Monarch Butterfly (Danaus plexippus) is a widespread tropical insect that ranges as far north as Canada. It cannot withstand freezing winter temperatures. To survive, monarchs migrate to safe overwintering sites that are neither cold enough to kill it, nor so warm that it wastes precious energy flying too much.
Monarchs east of the Rocky Mountains spend the winters in high mountains in central Mexico. Monarchs west of the Rockies migrate to locations on the California Central Coast. En route, they may travel as far as 2,000 miles, covering one hundred miles per day, and flying as high as 10,000 feet. A mighty achievement for such a seemingly fragile insect!
Why is this migration so unique? In many migrating species, such as birds and whales, the same individuals travel the migration route year after year. In contrast, migrating monarchs have never been to their destination before. In fact, several generations of Monarchs have lived and died since last year's butterflies departed. Reduced daylight triggers the monarchs to hold off mating and migrate to survive the drop in temperatures. It is believed that delaying mating enables the monarchs to live longer to accommodate the migration. Adult monarchs can live up to 6 weeks, but the migrating adult monarchs can live up to 6 months. No one knows how the monarchs migrate to the same places each year.