Monarch Butterfly Migration

Every year, up to 1 billion monarch butterflies (Danaus plexippus) migrate from Canada and the United States to specific mountain forests in central Mexico — a journey of up to 4,000 km. No individual butterfly makes the round trip; it takes four generations to complete one full migration cycle, yet each successive generation navigates precisely back to the same forests. The monarchs use a time-compensated sun compass and Earth's magnetic field to navigate. At their wintering sites in Mexico, they cluster in such density that trees appear orange, bending under their weight. Habitat loss, pesticides, and climate change have reduced monarch populations by 80% since the 1980s.