Summary
The lepidopteran family Arctiidae contains a number of species that emit high frequency sounds when tactually stimulated or exposed to the intense hunting cries of insectivorous bats. The sounds are produced as rapidly repeated clicks generated by the buckling action of the row of striae or microtymbals on the surface of the modified metepisternum (tymbal). The sounds seem to act as aposematic cues to discourage nocturnal, ultrasonically sensitive predators such as bats. Flying bats will avoid otherwise palatable prey (mealworms) when accompanied by the recorded sounds of arctiid moths. If bats play an important role in the evolution of sound production in arctiids then bat activity levels in an area should influence the phenology of acoustically active arctiids there. By examining the incidence of some silent and sound-producing Nearctic arctiids and its relationship to ambient levels of bat activity, some of those influences can be demonstrated.