Ultrasound avoidance is an escape or avoidance reflex displayed by certain animal species that are preyed upon by echolocating predators. Ultrasound avoidance is known for several groups of insects that have independently evolved mechanisms for ultrasonic hearing. Insects have evolved a variety of ultrasound-sensitive ears based upon a vibrating tympanic membrane tuned to sense the bat's echolocating calls. The ultrasonic hearing is coupled to a motor response that causes evasion of the bat during flight.
Although ultrasonic signals are used for echolocation by toothed whales, no known examples of ultrasonic avoidance in their prey have been found to date.
Ultrasonic hearing has evolved multiple times in insects: a total of 19 times. Bats appeared in the Eocene era, (about 50 million years ago); anti-bat tactics should have evolved then. Antibat tactics are known in four orders of Insecta: moths (Lepidoptera), crickets (Orthoptera), mantises (Dictyoptera), and green lacewings (Neuroptera). There are hypotheses of ultrasound avoidance being present in Diptera (flies) and Coleoptera (beetles).