Cicadas, cicadas, cicadas

Photo – Australian Museum cicada specimen, Toby Hudson

By Dr Jean Holley,

If you are situated anywhere in NSW right now, or perhaps any place where Summer has arrived, you would be familiar with the magnificent chorus of cicadas that are filling the summer airwaves. Some days, I canโ€™t stand in my backyard for too long as the sound can be quite deafening. I have found at least four species of cicadas at our place, and have been keeping my eyes peeled for more.

So why do cicadas sing? And how do they do it? Before we look at that, lets look at where cicadas fit in the taxonomic scheme of things (I canโ€™t resist the chance to look at some insect classification!). Cicadas are insects, and they belong in the rather diverse insect order, Hemiptera, which includes things like leaf hoppers, scale insects, aphids and cicadas. In Australia, there are around 350 species of cicada that have been identified, most of which belong to the one family, the Cicadidae.

Photo – Cicada Nymph, Graham Wise, WikiMedia

Photo – Cicada shell, pxfuel.com

Cicadas produce sound using two vibrating drum-like membranes, called timbals, that are found on either side of their abdomens. Only male cicadas sing, and they do this to attract a mate. Each species has its own, distinctive call. After mating, females lay their eggs on tree branches. The newly hatched young (called nymphs) fall to the ground and burrow below the surface. Nymphs feed underground on the sap of roots for up to several years. A fully-grown nymph then digs its way to the surface, climbs onto a tree trunk, a brick wall, or any other suitable object, and sheds its skin. The adult cicada then leaves its old empty nymphal skin behind.

Adult cicadas only live for a few weeks. In contrast, the nymphs of some Australian species may live in the soil for 6-7 years. This may explain why cicadas are more abundant in some years compared to others. Did you know that the periodical cicadas of North America will spend 13 or 17 years underground? Amazing!