Function

Because of their physical properties, acoustic signals are highly adaptive for certain kinds of behavioral interactions: sound waves can travel at any time of the day or night, through thick vegetation or muddy water; they convey information instantaneously and can be transmitted over long distances; and sounds are easy to localize, do not leave lingering traces, and can transmit large amounts of information per unit time. For the majority of insects, acoustic communication functions primarily in reproductive behavior and predator avoidance, but may also be used for detecting prey or host species (parasitic flies, wasps; predatory water striders, ant lions) or calling to conspecifics to form aggregations (sawfly larvae) or warn of danger (termites, treehoppers).

For humans, the most conspicuous sounds commonly heard from insects are the loud chirps and trills of field crickets, the long raspy choruses of katydids by night, and the intense, shrill-like buzzes and rattles of cicadas by day. These are the mating calls emitted by males in order to attract conspecific females. Sounds used in reproductive interactions function in species recognition, courting, pair maintenance, female mate choice, and male—male competition. The hearing organs of crickets, katydids, grasshoppers, mosquitos, and cicadas are used primarily for these purposes and are sharply tuned to the calls of conspecifics. The features of these mating calls have surely been shaped by sexual selection.

Many insects have ears for the sole function of detecting predators. Many nocturnally active insects (most Lepidoptera, some mantids, beetles, and lacewings) have ears tuned to the ultrasonic vocalizations of insectivorous bats that use biosonar to detect and home in on their prey. Unlike ears specifically designed for conspecific communication, the ears of predator detectors are usually more broadly tuned and more simple in their design, sometimes having only a few auditory cells per ear.

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