Just don't get eaten
Moths have specialized hearing to detect the high-frequency calls of bats. Diurnal species that are no longer preyed on by bats lose their hearing ability over the course of evolution. Moth ears are not one of the most outstanding features of insects. They have specialized hairs or simple membranes that sense vibrations like our eardrums. But moths do not communicate by sound, and only one species is known to make defensive noises. It is therefore reasonable to assume that the moth ears are designed to recognize predators in good time. A study has now revealed evidence that this sense in moths is finely tuned to the sonar calls of bats (Journal of Comparative Physiology A, Vol.181). Diurnal moths, which are never threatened by bats, are almost always stone deaf.
Moths' simple ears are well-adapted to the high-pitched sonar calls made by bats pursuing their species. But this agreement alone does not prove that the ears do not have other tasks to fulfill. James Fullard of the University of Toronto and his colleagues think the strongest clue would be if those moths that bats never hunt are deaf. His working group therefore compared the hearing ability of seven diurnal moths and twelve moths. While the latter reacted very sensitively to the calls of tropical bats, the diurnal insects had significantly worse hearing, three species were even completely deaf in the frequency range examined.
Because the diurnal moths evolved from progenitors that were certainly part of the bats' diet, Fullard believes that the moths no longer needed their hearing ability when they began to fly by day. A few species of daymoth eventually have no ears at all. Possibly this is also the future destiny of the other species. Seems like in an environment without bats there's nothing for moths worth listening to.
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