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Tympanal Hearing in Insects
Insects hear through one of four ways, the most common of which is through a paired set of organs similar to our own eardrums called the tympanum, frequently located on the legs or thorax of the insect. Tympanal insects such as crickets, locusts, praying mantids and moths can hear a wide range of frequencies that extends well into the ultrasonic range -- moths in the Noctuidae family can hear up to 240,000 Hz. This allows them to hear bats as they echolocate prey at frequencies between 20,000 and 100,000 Hz.
Pilifer Hearing in Insects
Another way insects hear is through a unique auditory organ called a pilifer that is found on the head in certain species of hawk moths in the subfamily Choerocampinae. The pilifer's optimal frequencies are from 15,000 to 70,000 Hz, a comparable range to that of the tympanal organs.
Evolutionary Developments
Having the ability to hear the sounds of predators is crucial to survival. The hearing mechanisms of some insects evolved in direct response to the ultrasonic sounds emitted by bats to echolocate prey, while other insects have always had the ability to hear ultrasonic frequencies. Another predator -- the only terrestrial mammal known to echolocate -- is the shrew, which uses ultrasound to explore its environment. The ability of insects to hear frequencies up to 50,000 Hz emitted by shrews helps the insects survive.
Low-Frequency Hearing
Some beetles, moths, butterflies, praying mantids and lacewings also have the ability to hear very low frequencies. This allows them to communicate with their own species or avoid detection by a different species. Avoiding detection involves both hearing your predators as well as staying under the radar, so to speak, by not allowing your predators to hear you.