By Meghan Rosen
Scientists have pinned down the answer to a long-standing butterfly mystery: what flips monarchs’ migratory compasses. A little cold weather may be all that’s needed. Just 24 days in a chilly lab incubator is enough to switch a butterfly’s flight orientation from south to north, researchers report online February 21 in Current Biology.
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“It’s pretty doggone cool,” says insect ecologist Orley “Chip” Taylor of the University of Kansas, who was not involved in the new research. But the finding is also disturbing, he says. “It suggests that as temperatures warm, monarchs may be in trouble.”
Each fall, in a massive monarch migration, millions of butterflies set off on a journey from their northern range to central Mexico to escape freezing winters. Nestled among Mexico’s Michoacán mountains, the butterflies cling to tree branches, huddled together in roosts to fend off the cold. “They sort of snuggle each other,” says study author Steven Reppert of the University of Massachusetts Medical School in Worcester. The snuggling creates a cozy microenvironment that buffers high and low temperatures.