The sound of death can take many forms: the retort of a gun, the screech of tires, the hack of a cough. But for many moths, death sounds like a series of high-pitched squeaks.
Moths are hunted by bats, which track them down by releasing high-frequency calls and analyzing the rebounding echoes. This skill, known as echolocation, allows them to view their world—and their prey—even in total darkness. Bats evolved the ability to echolocate tens of millions of years ago, and in the intervening time, moths have developed their own countermeasures. Some evolved ears, which allow them to eavesdrop on the calls of hunting bats and take evasive action. Others play the bats at their own game, releasing their own ultrasonic clicks to jam the radar of their predators, or to feign the echoes of distant objects.
Bats, in turn, have evolved their own tricks for circumventing the moths’ defenses. Some, for example, use stealth.
Bat calls are too high-pitched for us to hear, and we should all be grateful for that because they’re also some of the loudest sounds produced by any animal on land. If we could hear them, it would be like listening to a passing ambulance, a jackhammer, or a rock concert. But Townsend’s big-eared bat—a North American species with a foot-long wingspan—is an exception. Aaron Corcoran and William Conner from Wake Forest University have found that when it hunts, it does so at a whisper, with very quiet calls that moths can’t hear. It has evolved into a winged ninja—silent and undetectable, until it’s too late.