After 17 years underground, billions of cicadas are about to descend upon the U.S. Midwest, crowding the trees and filling the air with their distinctive mating call.

But the usually punctual Brood XIII bugs are emerging about a week ahead of schedule—which has some scientists pondering how a changing climate might alter the cicadas' little-understood life cycle.

 

"The fact that our Aprils are warmer than they have been in the past is apparently encouraging the cicadas to emerge a week or so earlier than they have in the past," said Gene Kritsky, a biologist and cicada expert at the College of Mount St. Joseph in Cincinnati, Ohio.

A Puzzling Cycle