Nocturnal anti-predator adaptations in eared and earless Nearctic lepidoptera

Nocturnal flight exposes insects to selection pressures that include reduced light and the hunting behavior of insectivorous bats. Using a phylogenetically based selection of wild moths collected from a Nearctic site, we report that earless species fly less throughout the night than eared species. This supports the hypothesis that this behavior has evolved as a passive defense against the transient attacks of aerially foraging bats in insects that do not possess long-range auditory detection abilities. We measured the eyesize of a selection of moths whose 24-h flight activities are known and confirm that nocturnal lifestyle results in larger eyes. With the exception of hawkmoths, there is no eyesize difference between eared and earless moths, suggesting that earless moths do not preferentially use vision to detect the approach of bats.