Most butterfly species live and die within a narrow geographic range, because their brief life span allows little time for wandering. However, the monarch butterfly migrates thousands of miles from southern Canada and northern parts of the United States to Mexico and southern coastal California. The round trip takes two or three generations to complete, because of the short individual life span. Each butterfly must find its own way, having no living guide, yet the species follows the same broad migratory route year after year, century after century. Monarchs and some other butterflies migrate in massive numbers, forming clouds of color sometimes a mile wide and a mile long; millions perish during the journey.