Auditory influences on the flight behaviour of moths in a Nearctic site. II. Flight times, heights, and erraticism

Abstract

While moths that possess ears protect themselves from bats by listening for their echolocation calls, earless species presumably use different defences. Tent-caterpillar moths (Lasiocampidae) are earless and emerge in very large numbers at our Nearctic site. One species, Malacosoma americanum, has a nightly peak emergence time mismatched to the peak activity times of certain sympatric bats, while that of another, M. disstria, is more coincident with that of the bats. These data suggest that while both species swamp bats with their large numbers, M. americanum gains additional protection by temporally separating itself from bats. Empirical flight observations and sticky-trap captures indicate that earless moths fly closer to the ground and more erratically than eared moths, although exceptions exist (e.g., high-flying sphingids and erratic geometrids). The foraging habits of most sympatric bats predict that small moths, in particular, will benefit from this behaviour. We suggest that low-altitude erratic flight in moths is a protean insurance defence against bats, as it should reduce the chance of their being detected by these predators.