Saturday, June 02, 2007

A Ventriloquist In The Grass

Anyone who has walked in the country on a summer's day or evening will have heard the seemingly endless chirping of grasshoppers and crickets. Grasshoppers call mainly during the day, crickets at dusk. Children attempting to capture a cricket are often thwarted by the insect's ingenious ability to 'throw its voice' like a ventriloquist. If it senses danger nearby, a cricket can alter the pitch of its calls giving the impression that the sound is coming not from the insect itself, but from a spot some distance away.

Crickets' chirping comes entirely from males competing among themselves and advertising their presence to potential mates. In many species of grasshopper, however, the male's song is answered by the female.

There are two basic methods of producing these penetrating chirps. Both are forms of stridulation, rubbing parts of the body together to produce a sound. Short-horned grasshoppers rub a row of tiny pegs on the inside of their hind legs against veins on their front wings, like someone playing a washboard in a jazz band. The same rough and ready technique is used by their close relatives, the locusts.

Volume control

Crickets have superior musical equipment, located on their two front wings, which they shuffle rapidly together. Each wing has a vein bearing a ow of teeth, which are rasped across a kind of scraper or plectrum on the edge of the other wing, producing a very pure, high-pitched pulse. Each 'chirp' is made up of a rapid succession of these pulses. A smoothly polished part of the wing membrane is used to amplify the sound. When the wings are raised during stridulation, the space between them and the body serves as a resonating chamber. It is by varying the size of this space that these insects are able to make their chirps appear to come from nearer or farther away.

Did you know that crickets have no ears to hear. Crickets hear through membranes on their front legs.

1 comment:

bluelunareagle said...

Fascinating! I have always wondered about these ventriloquists - often so loud and yet so mysterious. Thanks for illuminating me. Many thanks, too, for your feedback on and the poem for my mum. All the best!