There are moments when summer can seem a quiet time in the bush...

Many plants have died off or shriveled back to underground storage organs while many bird species have retreated to moister refuges. But don’t be fooled, summer is full of life if you look hard enough, as this is the most prolific time for most of our invertebrates.

Like reptiles, invertebrates are ectotherms, meaning they can’t warm their body temperature like mammals and so rely on outside temperature to do the job for them. So over summer we see so many groups within the insect world flourish, including moths, butterflies, beetles, ants and all kinds of bugs.

But one of my favourite summer creatures has got to be the cicada, whose loud calls fill the bush with sound. Cicadas are fascinating little critters. Their life cycle begins when an adult cicada lays its egg in a slit cut into the bark of a tree or a stem of a grass or herb. After several months the pronypmhs hatch and make their way to the entrance of the slit and within minutes shed their first skin to enter the true nymph stage. They then drop to the ground where they search for a crack in the ground, and once entering they don’t see the sunlight again for several years. Indeed, some cicada nymphs have been recorded staying beneath the ground for over 15 years!

Beneath the ground the nymph constructs a small chamber, somewhere between 40-100cm deep, which is always located adjacent to a root of the food plant. You see, like many butterflies that have specific food plants, most cicadas only feed on the roots of particular groups of plants. Throughout Australia the most favoured food plants are Eucalypts, wattles and a range of native grasses. So the larvae remains feeding on the roots for a number of years before eventually emerging during warm weather. They then take to the bush and perch in the shrubs and trees where the males begin playing their song to attract a mate by using a rapid rhythmic buckling of their tymbals (a pair of ribbed membranes).

The song of many species can be very loud and has been shown to repel some predators such as birds because the noise is painful to their ears. Common Victorian cicada species include the Redeye, Psaltoda moerens, Green Grocer, Cyclochila australasiae and the Ticker, Pauropsalta rubistrigata. The Greengrocer is one of the loudest insects in the world and due to its ability to feed on introduced as well as native trees it is relatively common even near Melbourne CBD. The Redeye is very conspicuous in the peak of summer throughout large parts of Victoria, its constant call like a bush mantra. Other calls are less conspicuous due to their high pitch, such as the call of the ‘Squeaker’, Pauropsalta infuscata.

Some cicadas also supplement the sounds made with their tymbal action by clapping their wings such as those in the Cicadetta tigris group. What master musicians! The cicadas musical abilities have been admired for thousands of years, as told in the Greek myth of Eunomos. This ancient musician was playing his cithara (an ancient instrument of the lyre family) in competition when one of the strings broke. But luckily for him a good-natured cicada turned up and landed on the instrument, sustaining the sound of the broken string with its call!
Karl Just

Information sources

Australian Cicadas by M.S Moulds
Melbourne’s Wildlife, a field guide to the fauna of Greater Melbourne

Museum Victoria
http://geoffpark.wordpress.com/2010/01/27/identifying-our-local-cicadas/
http://en.wikipedia.org/wiki/Cicada_%28mythology%29