October’s falling temperatures trigger the annual migration of millions of monarch butterflies across the continent. Every fall, these lovely butterflies fly thousands of miles from as far north as Canada to overwinter in California and Mexico. When swarms of monarchs pause en route to rest and feed on nectar-bearing plants, admirers will see them blanket trees and shrubs in orange and black. Photo of a monarch butterfly chandelier in California by Joanna Gilkeson, U.S. Fish and Wildlife Service.