in the style of Smithsonian's Wild Life

Timed Flight

How do tiny monarch butterflies migrate more than 2,000 miles without a map and end up in the same grove of fir trees in central Mexico, year after year? They navigate by the sun, just as the Vikings did. The monarchs’ internal sun compass needs a clock to work correctly because the sun is “a moving target, and butterflies need to compensate for that movement,” says Steven Reppert of the University of Massachusetts. Until recently, scientists assumed that butterflies navigated with a light-sensitive clock built into their brains. Reppert and his colleagues discovered that monarchs have two such clocks – and that they navigate with the one in their antennae.

The researchers put tiny leashes on the monarchs and let them take wing in an outdoor flight simulator. Normal butterflies flew southwest, toward Mexico. Butterflies with their antennae snipped off couldn’t orient properly and took off every which way. Painting the monarchs’ antennae black didn’t affect their brain clocks, but a few days without time cues from the sun set the butterflies and their antenna clocks adrift. Bees, ants, and other insects that navigate by the sun may rely on antenna clocks, too.