Sound engineers of the insect world

In his quest for a mate, the male cricket, a skilled communicator, sings three different songs: one to advertise his presence, one to court and one to ward off unwanted competitors.

First comes the calling song, a high-frequency sequence of simple chirps that is maintained for as long as it takes to attract attention. Should a female show interest by approaching, the male increases the frequency and shortens the duration of each note. This results in an excited buzz which seems to entice the female cricket.

If a male approaches, this song gives way to another, more aggressive outburst in which each chirp is drawn out in an expression of self-assertion.

Females, for their part, are well adapted to pick up these signals. They use different receptor cells in their ears and nervous systems to distinguish between the songs of competing males, and will travel right through the territory of an unwanted partner to a male that produces a more attractive song.

The male cricket produces his songs by 'stridulating' or rubbing together specially adapted areas at the base of his wings. On the underside of one wing is a row of teeth-like protrusions similar to a comb; on the edge of the other lies a tongue of toughened tissue. The tongue acts like a guitar plectrum. Each time it strikes one of the teeth it creates a sharp click. This sound is then amplified and transmitted by a resonating part of the wing called the 'harp'. The rate at which the plectrum strikes the teeth gives the songs the distinctive quality of each species.

The male grasshopper uses similar means to amplify his mating songs, but the method used to make them is different. He calls by scrapping rows of tiny pegs on his back legs against a thickened vein on the forewing. Each species of grasshopper has its own call which is determined by the arrangement of pegs and the rate at which they are scraped. The number of pegs also varies from 80 to 450 per leg.


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