Caterpillar twitches in an ultraquiet chamber are helping biologists understand how these insects hear without ears

A tobacco hornworm caterpillar is exposed to vibrations in an anechoic chamber. Binghamton University, State University of New York

In a quiet summer garden, a caterpillar perches on a branch, munching serenely on leaves. A moment later it freezes. It senses danger – and just in time. From behind, a wasp approaches, sizing up its prey.

Tobacco hornworm caterpillars don’t look like they have ears, and yet they’re able to sense predators such as wasps. How does the caterpillar know a wasp is approaching?