The ears of the praying mantis are easily overlooked, even by entomology experts. Until the research of Yager and Hoy in the late 1980s, (Cell Tissue Res (1987) 250:531-541), the mantis was not known to be capable of sound detection. The praying mantis uses crypsis (blending with its surroundings) to stalk and capture unwary insect prey and to hide from predators of all sorts. Making noise would be counterproductive. Mating in the praying mantis involves release of pheromone by the female and does not depend on sound like mating in grasshoppers and katydids.
Why does the praying mantis have ears? Its camouflage is very effective against visual predators when it is stationary. Its camouflage is not at all effective when it flies. In daytime, predators such as birds are abundant. It is safer for the mantis to fly under cover of darkness. However, dangerous predators patrol the flyways at night- bats. Bats prey on many insects including the praying mantis. Bats use sonar (sound waves) to locate and capture flying insects. The ears of the mantis warn of approaching bats and allow the mantis to take evasive action.
Yager and Hoy investigated the unusual structure of the underside of the praying mantis thorax and determined that it was a sound detection organ. The segment of the thorax that contains the middle legs of the mantis has a shallow groove that leads to an even deeper groove between the hind legs of the mantis. The deep groove contains the mantis ears. Each side of the groove contains a thin area of cuticle that vibrates in response to sound waves, including the sounds made by bats. Inside the mantis, air sacs are aligned next to the cuticle of the groove. When the cuticle of the groove vibrates, it causes the underlying air in the air sac to vibrate and the “sound” is received by the mantis nervous system.
The configuration of the mantis ears probably does not allow the mantis to get directional information about the bat. However, evading bats involves adjustments in flight, commonly sharp non-directional turns or to enter a steep “power dive” to the ground. For these movements, knowing the bat’s direction of approach is not as important as just knowing the bat is nearby.