These moths that beat the drum to keep bats away


An ermine, a moth of the genus “Yponomeuta”.  With each beat, the two hind wings strike the edge of the “clear windows” (arrows) like a drumstick on a drum.

SSixty million years this lasts! Since insectivorous bats acquired the ability to find their way by echolocation, their favorite prey, moths, have developed countermeasures. Evolution has spared no effort in the imagination. Certain species are endowed with an exceptional capacity for camouflage. Their hairs or scales absorb the ultrasound emitted by bats. Deprived of echo, predators can no longer spot them in the night. Others use scrambling. As soon as they detect the clicks of the bats, they in turn emit waves which disrupt the analysis of the attacker. Still others seem to have a lure, namely a long twisted tail which would attract the bat… and detach after impact.

The group of Yponomeuta and its thousand or so species have adopted a radically different strategy. Not to hide, nor to deceive the adversary, but to make oneself seen, or rather heard. The technique is well known among butterflies and even frogs. It even has its scientific name: aposematism. A two-sided strategy. On the other hand, being detestable, in the taste sense of the term, either particularly bitter or downright toxic. On the face side, let the predator know. Wear the most visible colors possible and fly slowly, just to avoid being bitten by mistake.

But at night, all butterflies are gray. Yponomeuta therefore transferred this strategy to the sound world. To let people know that it is better not to approach a tooth, butterflies emit particularly powerful clicks. In recent studies, the team of biologist Marc Holderied, at the University of Bristol, established that these impulses reached a decibel level equivalent to that of a conversation between humans and that they were perceived by the ear from the bat at a distance of 7 meters. The flying mammal, moreover, is not mistaken, and actually avoids the clicker at dinner time.

Continuous clicks

As if this painting lacked richness, Yponomeuta presents another particularity, that of being deaf. Clicks cannot therefore serve as a means of communication between individuals. It is indeed intended for bats that they are issued. For the same reason, the moth cannot reserve its countermeasure for moments when the predator is approaching… since it does not hear it. So much so that it clicks continuously.

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