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Cicada Noise

Date: Sunday, June 02, 2002

Tolla Niemand of Springs wants to know if cicadas (sonbesies) - those creatures with that high-pitched ear-piercing noise - can hear the noise they make.

Prof Martin Villet - Rhodes University
Cicadas are the loudest insects in the world. They can reach sound levels of up to 120 decibels. Can the hear themselves? Not while they are calling. They have ears on the side of their abdomen and when the male is calling - only the male calls - there is a little muscle in the ear that pulls on the membrane and makes the ear effectively deaf.

And it is quite interesting to see how they produce the sound that pierce our ears, if not their own.

Prof Martin Villet
There are membranes on the side of the body responsible for making a kind of clicking noise. There is a big muscle inside the body that pulls on these membranes.

The membranes on the side of a cicada can be thought of like the sides of a plastic jar. When the muscle on the inside pulls the walls in it makes a clicking noise - and again when it relaxes. Depending on how stiff those membranes are the noise produced will have different frequencies. The bigger-bodied cicadas will often produce deeper calls than the small-bodied cicadas. So, you will find different species actually have different pitches in their call and their ears are tuned in to hear their particular call.

One of the anomalies of cicada calls is that they can in fact only hear one sound frequency, whereas humans can hear a whole sound spectrum.

Prof Martin Villet
So, in fact the cicada is tunes in to hear what it needs to hear and when it is calling it doesn't hear anything.

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