Producing ultrasound is a common defensive strategy against bats employed by several moth taxa, but there are a number of ways sound is used. For example, many larger moth species’s hearing is specifically tuned to hear approaching bats’ echolocation calls, and immediately upon hearing such calls, the moths respond by performing evasive mid-air maneuvers. Other moths have long hindwing tails that produce decoy echos that create false targets, so the bats preferentially attack the moths’ hindwing tails.

“Bat defences in larger moths are well studied, however, the defences in smaller moths are not,” said lead author Liam O’Reilly, a PhD student at Bristol’s School of Biological Sciences.

The genus, Yponomeuta, includes 100 or more species of moths that range in size from super-tiny to medium-sized moths, most of which fly at night. These moths are poorly known (because they are so small), but one characteristic that they all have is a translucent patch that is devoid of wingscales at the base of their hindwings. It was originally proposed that this translucent patch may produce sound so the moths could evade attacks by bats, but no one knew if this was the situation because the acoustic arms race between any of the micromoths and their bat predators has not been investigated before.

Mr. O’Reilly and his collaborators investigated the significance of the Yponomeuta micromoth species’s translucent wing patch and identified the acoustic properties of the sounds it produced.