Y: Y’know Don, bats are the terror of the night sky. They hunt in darkness, using sonar echolocation to detect and intercept flying insect prey.
D: Right Yaël, among insects, most moth species are active at night. It must be really dangerous to be a moth.
Y: Yes, but moths have evolved numerous ways to protect themselves. Many moth species have ears that can hear the bat’s sonar pulses and take evasive action. But many are deaf. In 2018 a team of British scientists reported a new way that these moths protect themselves- acoustic camouflage.
D: So, just like camouflage makes things hard to see, acoustic camouflage makes the moth hard to detect with sonar?
Y: That’s right. Moths and butterflies have similar wings, but most butterflies are active during the day and don’t face the threat of bat predation. When the researchers compared the sound-reflecting properties of moths and day-flying butterflies, they found that nocturnal moths have special adaptations to reduce the amount of sound they reflect at the ultrasonic frequencies of bat sonar. They can absorb up to eighty five percent of incoming ultrasound, compared to only twenty percent for butterflies.
D: How do they do that?
Y: Moths have scales on their bodies and around their wing joints that is thicker and denser than for butterflies. The scales are like fur, and absorb sound. Removing it increased a moth’s chances of being eaten by a bat by thirty eight percent. The researchers found that the scales of moths are structured, on the microscopic level, so that they vibrate at just the right frequencies to cancel out the ultrasound frequencies of bat sonar.