• Wildcreatures

What body parts do you rub together...to make a noise?

I'm talking to a Cicada here, or course, as the noise they make is quite special, as it is not made by rubbing its body parts together.

The great insect noise you are hearing now is almost certainly down to the earliest of the Cicadas to appear, the Spotted Black Cicada, Gaeana maculata, first “described’ in 1773, from China, seen in these picture above..

Cicadas are amongst the loudest insects known to man, and a swarm of them can produce sounds up to a staggering 120 decibels. For comparison a rock concert in Hong Kong is about 115 decibels. This sound can be compared to the noise from a chainsaw (humans start to experience pain from sound at the 120 decibel level).

Now, about how they make that sound...

As you may have found out, the Cicada has an exceptionally loud song, produced not by stridulation, but by rapidly vibrating drumlike tymbals rapidly. This post will go on to describe exactly how they make such a loud noise. Another reason why they are so loud is that they hatch at the same time, and can be seen in great numbers, swarming up trees and plants.

The "singing" is done by the male cicadas. Most species of insects, crickets for example, produce their sound through stridulation (rubbing body parts together). However, our noisy friends have a resilin structure called a tymbal at each side of its rear end. The tymbals are part of the exoskeleton formed into complex membranes with thin, membranous portions and thickened ribs. As they contract their internal muscles this buckles the tymbals inwards, thereby producing a click; on relaxation of the muscles, the tymbals return to their original position, producing another click. Adding to this, their abdomens are mostly hollow, and this acts as a sound box. By rapidly vibrating these membranes, a cicada combines the clicks into apparently continuous notes, and enlarged chambers derived from the tracheae serve as resonance chambers with which it amplifies the sound. The cicada also modulates the song by positioning its abdomen toward or away from what it is sitting on. Partly by the pattern in which it combines the clicks, each species produces its own distinctive mating songs and acoustic signals, ensuring that the song attracts only appropriate mates.

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