In crickets,
one wing covers another, a pair for each side of the body. The cricket's
song is made when these pairs are rapidly opened then closed using a specia
rhythm; the closing stroke rubs a specially designed scraper against a "file,"
a series of ridges on one of the prominent veins in the lower wing. The
produced sound is then amplified by two regions in the lower wing called
the "harp" and the "mirror," both of which vibrate
to the sound produced by the scraper and file. "The relatively small
amplitude of vibration generated during stridulation may be considerably
increased by the resonance of the radiator" [Michelson and Nocke, 258].
These devices in the wings are constructed of chitin, a semi-transparent
bone-like substance part of the insect's exoskeleton.
Crickets have
many different songs, including rivalry and courtship songs. Not much is
known about how these different songs are produced (with the same equipment)
or what their actual social functions are.
Stridulation = friction causing sound. "Sound waves may be described
as alternate compressions and rarefactions." "The information
carried by sound may be coded as frequency, intensity, and time."
phonotaxis: locomotion turning toward a sound source, as in a female
cricket moving in the direction of a male's song
The Tuned Singing Burrow of Mole Crickets
There is one kind of cricket, the "mole
cricket," that uses another means of amplifying its song. "They
are the only known insects to modify their surroundings for acoustic purposes.
They build their burrow as a double exponential [with double openings] horn,
... [which] acts as an acoustic transformer considerably increasing the
efficiency of sound emission by the harps vibrating at the horn throat."
The burrow's double opening helps ensure wide distribution of the amplified
sound, and a "bulb" or bulbous widening of the burrow around where
the cricket's head will go allows the cricket to slightly "tune"
the sound by increasing or decreasing the side of the surrounding chamber
in the earth.
To use the burrow, the cricket digs it as it has learned, then crawls in
head first, so that its vibrating wings (over the rear of its body) face
outward, just below where the burrow forks into two openings, a few millimeters
from the surface of the ground [Michelson and Nocke, 265-66].
Primary source: Axel Michelsen and Harald Nocke,
"Biophysical Aspects of Sound Communication in Insects," Advances
in Insect Physiology (New York: Academic Press, 1974), pp. 247-96.
See also Vincent Delthier, Crickets and Katydids, Concerts and Solos
(Cambridge: Harvard UP, 1992).
