butterfly clocks

Monarch butterflies are famous for their thousands-mile-long fall migration from eastern North America to central Mexico. But how do they know how to get there? Scientists knew that the butterflies used the sun to navigate, but they weren’t sure how the monarchs adjusted direction as the sun’s position in the sky changes. Researchers from the University of Massachusetts Medical School may have solved the mystery. In the May 23 Science, they show that monarch butterflies have internal “circadian” clocks that help keep them on their proper course. In the experiment, monarch butterflies were housed under various light conditions as they developed from caterpillars to butterflies: some were kept in normal light conditions, some in constant light, and some with the “day” set with light from 1 a.m. to 1 p.m. Then the butterflies were placed inside a specially designed flight simulator, where their flight direction could be measured. Those subjected to normal fall sunlight flew in the normal, southwest direction, toward Mexico. Those subjected to constant light always flew toward the sun. Those subjected to the earlier light cycle flew to the southeast. Light apparently sets the butterfly’s internal clock. Study author Steven Reppert stated in a press release that the new findings “will help tease apart the entire migratory process, a process that remains one of the great mysteries of biology.”

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 6/03/2003.