The great North American migration: a butterfly extravaganza

It is perhaps the quietest animal migration on earth, so quiet in fact that until the 1970s no one even knew it happened. Every fall monarch butterfly populations of the United States and southern Canada head south to overwintering sites in Mexico. They go in search of food and warmer climes, a migratory journey that can take these delicate creatures two months to complete. Some will have traveled 3,000 miles, a seemingly formidable task for such a small and delicate a creature as a butterfly.MonarchInMexicoThen, each March the next generations of monarchs return north, arriving home in July, having flown 50 to 100 miles every day for several weeks helped only by the wind and their fat reserves. It is the only butterfly known to perform such a migration, more likely seen in birds and larger animals, and although monarch butterflies can be found across the globe, the great North American migration is carried out by just one subspecies increasingly threatened by habitat loss and disease.MonarchMigrationMap

They roost in huge numbers climbing into the millions on oyamel fir trees in just a few special mountain sanctuaries such as Sierra Chincua outside of the town of Angangueo in central Mexico. Completely covering the trees, they have been known to break the branches of the oyamels with their combined weight, despite the fact each individual weighs less than a gram. Even more astonishingly, the butterflies arrive at the same trees generation after generation, somehow knowing their destination without ever having seen it for themselves.monarchPairBonSecourRefugeThe oyamel trees – also known as the sacred fir – create a microclimate which protects the butterflies from the worst of the weather, preventing temperatures rising too high or dropping too low, while clustering together also helps the creatures keep warm. To see the dark orange stained-glass patterning of the wings huddled among others on the trees, or the insects sweeping around the forest like the dropping leaves of fall is one of nature’s most astonishing spectacles.Metamorphosis MonarchOnNewEngland images: