There are over 200 species of cicada in Australia, and their noise can be truly deafening. Their chorus can be up to 120 decibels, which is painful and bad for your hearing.
It is thought that their noise might be at this level to deter predators. It's likely to be loud enough to be painful to birds' ears and interfere with their communication. Last week, in the Grampians we were in the midst of the cicada season, and we took to wearing ear plugs.
They sing in chorus to make it harder for a predator to locate an individual.
Insects such as grasshoppers and crickets make their noise by rubbing - stridulating - one body against another, like part of a wing on part of a leg. Male cicadas instead, have a little stripy membrane called a tymbal in their abdomen. Muscles buckle this back and forth like one of those clicky toys with metal strips. The sound resonates in the large cavity of their abdomen.
This makes them extremely noisy, and apparently helps them find a mate. You could say it's the insect equivalent of a loud car.
The cicada song is unique to each species. The females recognise this so they don't waste time cuddling up to the wrong type. It's remarkable that even with their minuscule brains, they're able to tell which is the right song.
Cicada hearing apparatus consists of a pair of large mirror-like membranes called tympana. These are connected to an auditory organ by a short tendon, and the male to use this so he doesn't deafen himself.
Interestingly, we humans also have small tendons in our middle ear to dampen our own speech. It's an example where two very different species have evolved similar solutions to solve similar problems.
Fortunately, human voices are not so loud, and normal speech peaks at about 65 decibels.
That's not difficult, but imagine being near Annalisa Flanagan, who holds the world record for the loudest shout. 121 decibels. Don't make her angry.
Response by: Rod Taylor
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