In summer, the night air is filled with the sounds of chirping crickets. The chirps are the love songs of the male crickets hoping that the female cricket of their dreams will hear their lonely song and respond.
Insect hearing has similarities and differences with human hearing. Our ears are on the side of our head. Inside our ear is a membrane, the ear drum, that vibrates in resonance to vibrations in the air.
Female crickets have membranes that vibrate in response to sound. Their membranes respond maximally to the sound produced by male crickets. Crickets that are better at finding mates are more likely to mate and produce offspring. Crickets that cannot find mates do not produce offspring and their genes are not passed to the next generation. Every generation, those genes best enable crickets to find mates are the ones that are passed to the next generation. Over time, this leads to refinements in the sound detection organs that produce a very fine tuned system.
Unlike people, who have ears on our heads, crickets have their “ears” on their front legs. All sound detection systems are better able to determine the direction of a sound if their are at least 2 detectors and they are far apart. Thus, the ears of crickets are located on the front legs. This allows the sound detectors to be further apart. The membranes are in pits in the front legs and have directional sensitivity. They are most sensitive when directly facing the location of the sound and less sensitive as they are rotated away from the sound direction.
Directional sensitivity enables crickets to determine if the mating call is coming from the left or the right. If the sound is louder in one ear than the other, the cricket will turn its body. When the body is directly facing the location of the mating call, the response of the two detecters is equal. A mate will be found by moving straight ahead.
The next time a cricket keeps you awake at night, think of the lonely males desperately calling out their love songs and the female crickets listening in the dark. It may help you go back to sleep.
The leg of a cricket showing the location of the ear (arrow)