Peacefully munching on leaves, caterpillars seem like the quiet type. But a new study reveals that they sound off during contests over living quarters, providing the first evidence that these insects use sound to communicate.
Caterpillars have shed their image as antisocial eating machines. In fact, many species live communally, and some may duel to the death for possession of tasty leaves. Still a question mark, though, was whether caterpillars chitchat.
Zoologist Jayne Yack and colleagues at Carleton University in Ottawa, Canada, eavesdropped on the larvae of the widespread hook-tip moth. They typically stake out a leaf and fashion a shelter by joining the edges of the leaf with silk. Yack and her colleagues staged confrontations between the owner of the pup tent and a homeless bully seeking to oust it.
The monitoring revealed that a hook-tip caterpillar is a veritable percussion section. When an intruder approaches, the tenant begins rasping the leaf with oar-shaped structures on its abdomen. If that doesn't deter the invader, the caterpillar raps and then scrapes the leaf with its jaws. And if neither insect backs down, a protracted acoustic duel may result, the scientists report in the 18 September early online edition of the Proceedings of the National Academy of Sciences. In a quiet room, says Yack, the sounds are audible from 4 or 5 meters away. The sounds are territorial signals, not generalized "alarm" calls, Yack says, because the caterpillars remain silent during gusts of wind and sudden movements. Now Yack is trying to determine how the earless caterpillars detect sound.
"It's really exciting," says William Conner, an insect biologist at Wake Forest University in Winston-Salem, North Carolina. For the first time, we have tapped into what may be an important communication channel for these insects, he says. "Clearly, the insects know how to play their instruments."