For many people, the monarch butterfly is the most easily recognized butterfly, distinctive with its black and orange wings.  The color pattern is recognized by potential predators as well, signaling that the insect may contain poison from the milkweed on which it feeds as a caterpillar. Native to the Americas, the monarch has colonized such far flung locales as western Europe and Australia. Traditionally two main populations have been recognized: one east of the Rocky Mountains and one west. The eastern population migrates south to central Mexico, the western to California. Recently scientists have suggested that the two populations commingle extensively.

The monarch undertakes annual generational migrations.  In central Mexico, tens of millions of butterflies overwinter in less than 20 sites, gathering in 20-30 million per large roost.  They begin to disperse in late February and early March, mating and then flying north, usually making it to Texas before laying their eggs on milkweed plants. The next generation continues the migration, leapfrogging north until the third or fourth generation arrives as far north as Canada in May and June. This final generation migrates up to 2,200 miles back to Mexico, arriving in early November. They begin migrating singly, and then are slowly funneled into flocks as they converge on roosting sites. 

As they fly south, the butterflies may fly as high as 4,000 ft while riding thermals, averaging a stately 12 miles per hour.  Intermediary generations have an adult lifespan of only 4-5 weeks, but the final annual generation lives 5-7 times longer, making the long migration and then surviving to overwinter, mate, and return north.

Nature picture credits (left to right): Photo © Jennifer E. Dacey, University of Rhode Island, United States (Monarch on leaves); Photo © Steven Katovich, USDA Forest Service, United States (Monarch closeup).