Why Do Crickets Stop Chirping When You Approach?

How a Cricket Knows When a Predator Is Near

Cricket
Crickets can hear you coming, and will stop chirping as you approach. Getty Images/Corbis Documentary/Gary Ombler

There's nothing more maddening than trying to find a chirping cricket in your basement. It will sing loudly and ceaselessly, until the moment you approach, when it abruptly stops chirping. How does a cricket know when to stop chirping?

Why Do Crickets Chirp?

Male crickets are the communicators of the species. The females wait for the songs of the males to spur on the mating ritual. Female crickets do not chirp. Males make a chirping sound by rubbing the edges of their forewings together to call for female mates. This rubbing together is called stridulation.

Some species of crickets have several songs in their repertoire. The calling song attracts females and repels other males, and is fairly loud. The calling sound is only used during the day in safe places: crickets aggregate at dawn without the use of acoustic calling. These groupings are typically not leks, because they don't assemble for the sole purpose of mating.

The cricket courting song is used when a female cricket is near and the song encourages her to mate with the caller. An aggressive song allows male crickets to interact aggressively with one another, to establish territory and claim access to females present in that territory. A triumphal song is produced for a brief period after a successful mating and may reinforce the mating bond to encourage the female to lay some eggs rather than find another male.

Mapping Cricket Chirping

The different songs used by crickets are quite subtle, but they do vary in pulse numbers and hertzes. Chirp songs have between 1 and 8 pulses, spaced out at regular intervals. Compared to aggressive songs, the courtship chirps tend to have more pulses and shorter intervals between the pulses.

Crickets chirp at different rates depending on their species and the temperature of their environment. Most species chirp at higher rates the higher the temperature is. The relationship between temperature and the rate of chirping is known as Dolbear's law. According to this law, counting the number of chirps produced in 14 seconds by the snowy tree cricket, common in the United States, and adding 40 will approximate the temperature in degrees Fahrenheit.

Crickets "Hear" Vibrations

Crickets know when we approach because they are sensitive to vibrations and noises. Since most predators are active during daylight hours, crickets chirp at night. The slightest vibration may mean an approaching threat, so the cricket goes quiet to throw the predator off its trail.

Crickets do not have ears like we do. Instead, they have a pair of tympanal organs on their forewings (tegmina), which vibrate in response to vibrating air molecules (sound to humans), in the surrounding air. A special receptor called the chordotonal organ translates the vibration from the tympanal organ into a nerve impulse, which reaches the cricket's brain.

A cricket is always on the alert for predators. Its body color provides camouflage, usually brown or black to blend in with most of its environments. But, when it feels vibrations, it responds to the nerve impulse by doing what it can to hide best—it goes silent. Crickets are extremely sensitive to vibration. No matter how soft or quiet you try to be, a cricket will get a warning nerve impulse.

Sound to a human is nothing more than vibrations traveling through the air and reaching our ears. Think about the thumping of a loud, deep bass drum or the bass on your music system turned up. Humans can feel the music at that point. From this example, it is easy to see how noise and vibration are intertwined. Usually, in everyday life, humans will hear something first, but crickets will always feel it.

How to Sneak Up On a Cricket

If you are patient, you can sneak up on a chirping cricket. Each time you move, it will stop chirping. If you remain very still, eventually it will decide it is safe, and begin calling again. Keep following the sound, stopping each time it goes silent, and you will eventually find your cricket.

Sources

  • Boake, Christine R. B. "." Behaviour 89.3/4 (1984): 241–50. Print.
  • Darling, Ruth, A. "." The American Biology Teacher 63.1 (2001): 44–47. Print.
  • Doherty, John, and Ronald Hoy. "." The Quarterly Review of Biology 60.4 (1985): 457–72. Print.
  • Hoffart, Cara, Kylie Jones, and Peggy S. M. Hill. "." Journal of the Kansas Entomological Society 75.2 (2002): 123–31. Print.