This discovery helps to settle a question that’s been bugging Corcoran for a while. He and other evolutionary biologists often talk about evolutionary arms races, in which predators and prey evolve ever-more sophisticated measures and countermeasures to outwit each other. But while scientists have documented myriad examples of prey adapting around their predators, there are surprisingly few strong examples of predators doing the reverse. (These examples include the shocking powers of the electric eel, the snakes that have evolved to resist the poisons of newts, and the mouse that turns scorpion venom into a painkiller.)

Partly, that’s because it’s hard to show that predators are adapting to their prey specifically. For example, for decades, scientists have suggested that bats could shift their calls to higher or lower frequencies that moths can’t hear—and indeed, there are bats that do this. But higher-pitched calls give them a sharper view of their surroundings, and lower-pitched ones travel further and give a wider view of the world. It’s possible that such calls evolved to help bats navigate, and were only incidentally useful for subverting the ears of prey.

In 2010, Hannah ter Hofstede from the University of Bristol found a more unambiguous countermeasure. She showed that the barbastelle, a small European bat, is also a whisperer, with echolocation calls that are 10 to 100 times quieter than those of other moth-hunting bats. This seemed like a clear-cut case of an anti-prey adaptation, since there’s really only one advantage to quieter sonar: catching sharp-eared moths.

Ter Hofstede demonstrated this by tethering moths in small arenas, and hooking electrodes to the neurons in their ears that detect bat calls. These neurons typically fire when bats are around 19 meters away, giving the moths plenty of time to react. But those same neurons only detect barbastelles when they are 2 meters away, giving them just half a second to dodge. By then, it’s probably too late.

Probably. In these experiments, the bats never actually got to attack the moths—and Corcoran wanted to know what would happen if they did. He chose moths that are known to jam bat echolocation and tethered them to fishing lines, hanging them in large outdoor arenas that were surveilled by cameras and microphones. Then he waited for bats to approach.

The results were clear. Compared to the long-legged myotis, a similarly sized bat and a fairly typical echolocator, the stealthy Townsend’s big-eared made calls that were 20 to 40 decibels quieter. And as a result, they catch moths on 80 percent of their attacks. “That’s pretty unheard of for a bat attacking well-defended prey,” says Corcoran. “And the moths almost never exhibited their normal defenses. They very rarely do diving maneuvers, and they never made their jamming clicks.” And when the moths did try to dodge, they did so at a third of the distance for the big-eared than the myotis.