- Written by Nadia O'Carroll
Adult cicadas have stout bodies with 2 pairs of wings that are usually glassy, veined and transparent. Cicadas have 3 pairs of legs, large compound eyes, 3 small glistening simple eyes (ocelli) and small bristle like antennae. They feed through needle like mouth-parts called stylets, which pierce the surface of plants.
Species of cicadas often have colloquial names inspired by their colour and appearance – black prince, green grocer, tiger, yellow Mondays, floury bakers, red eyes, double drummers, cherrynose etc. Sometimes cicadas are also described as locusts but this term actually refers to migratory grasshoppers.
The well-known song of the cicada is a mating call, which is made only by males. A broken erratic distress call can also be emitted when an individual is captured. Each species has its own distinctive mating call, large species such as the double drummer and greengrocer can produce noise intensity in excess of 120 dB. Australian cicadas are the loudest insects in the world. Other smaller species have songs so high pitched that their song is beyond our hearing range. Organs called tymbals, which are ribbed membranes at the base of the abdomen, produce the cicada’s song. Contracting and relaxing the tymbal muscles produce a pulse of sound. Male and female cicadas can hear through a hearing organ known as a tympana, but the male also has the capacity to crease his tympana when he sings to prevent being deafened by his own song.
Cicadas provide a valuable food source for birds, other insects and animals. In fact it is thought that cicadas may congregate and sing together to repel birds and reduce predation.
Cicadas live most of their life unseen, underground. As cicada nymphs they usually spend 6 to 7 years at depths of between 1 and 2.5 metres burrowing and eating sap from plant roots. They shed their skin as they grow. When they reach full size they dig their way to the surface, usually at nightfall in early spring and summer, then they climb up from the ground and undergo their final moult when the adult cicada emerges. It is the last nymphal skin that is often seen clinging to trees. The adult cicada lives only a few weeks and after mating, the female cicada lays hundreds of eggs in slits made on plant stems. The eggs hatch and the small wingless nymphs fall to the ground and begin to burrow into the soil.
Many aspects of the nymph’s life underground remain a mystery. The length of time nymphs spend underground is usually 6 to 7 years but can vary from 9 months to 17 years, and even nymphs from the same batch of eggs may spend different lengths of time underground. The nymphs also emerge at certain times of the year, so they must be able to perceive seasons and yet when they are underground they are unable to experience seasonal changes such as day length, temperature, rain etc. It is not known how they determine when to dig their way to the surface but it is thought that the flow of sap may provide some indication of the time of year.
It is ironic that we think of cicadas as singing creatures of summer, open air and sunshine and yet they spend most of their time living a dark, solitary, silent life underground.