Hasn’t it been an amazing season for cicadas in some parts of the Blue Mountains?!
Cicadas and their empty shells seem to be everywhere. I am sure everyone is quite familiar with cicadas, so I thought I would search for some interesting facts that may not be well known.
- There are over 200 cicada species found in almost every part of Australia — from the hot and wet tropical north to the snowfields of Tasmania, from beach sand dunes to the driest desert. The plants they inhabit range from the tallest trees to suburban lawns, coastal mangroves to desert shrubs and include both exotic and native plant species.
However, cicadas are primarily tropical insects and most Australian species are found in the northern half of the continent. The great variety of vegetation types and local climatic variation found in north-eastern Queensland makes this the richest region for species. The area of greatest species diversity is within 100 km of Cairns. - The time at which cicadas appear throughout the summer season varies from species to species, but each will tend to emerge in the same month across the different states. Green Grocers/Yellow Mondays tend to come out early in November and die out by the end of December. Black Princes and Floury Bakers start off at the end of December and go right through to February or March, while Red Eyes can still be found in the middle of February.
- Cicadas produce the loudest sound of all insects in the world and are the only insects to have developed such a specialised means of producing sound. Some cicada species produce noise intensity in excess of 120 decibels at close range (Greengrocer/Yellow Monday and the Double Drummer). Other small cicada species produce sound so high in pitch that it is beyond the range of human hearing.
- It is believed that the sound produced by some communal cicada species could be a defence mechanism against predatory birds — the cicada chorus increasing the volume of noise and making it difficult for predatory birds to find individual Cicadas by their sound.
- Many species of cicadas sing during the heat of the day. The loud sound produced by some day-singing cicadas can repel birds, possibly because the noise is painful to the birds’ ears and may interfere with their own communication.
- Other cicada species only sing at dusk. These cicada species are often weak fliers (such as the Bladder Cicada). They may obtain some protection from predatory birds by confining their activity to the later part of the day.
- Only male cicadas sing, in an attempt to locate females for mating.
- Each cicada species has its own song, so as to attract its own species for mating.
- As well as the calling or mating song, many cicada species also use distress songs, which can be broken and erratic noises produced when an individual Cicadas have been captured by predators. A number of cicada species also have courtship songs, which are usually quiet calls, emitted only after females have been attracted nearby using the calling or mating song.
- While most cicada species take around six or seven years to emerge from underground, it may be from only nine months to 17 years or more, depending on the species.
- It is not really known what triggers cicadas to emerge from underground. It may be a combination of signals, which may include increased sap flow in plants, indicating that there is warm weather and rain.
- Mature cicadas often fall prey to spiders, wasps, ants, tree crickets, birds and bats. Cicada nymphs can also be parasitised by the larvae of Feather-Horned Beetles.
- Mature cicadas have two large compound eyes, situated one on each side of the head, and they also have three very small glistening simple eyes (ocelli) on the top of the head.
- The mouthparts of cicadas are enclosed in long, thin, beak-like sheaths. The sheaths pass backwards from the lower surface of the head between the legs when they are not feeding. They contain four fine, needle-like stylets used in feeding. Mature cicadas feed by piercing plant stems and sucking plant sap.
- According to Dr Moulds (Australian Museum), cicadas can suffer from insect venereal disease. The adults of some cicada species are susceptible to fungi of the genus Massospora. The entomopathogenic fungi attack the terminal portion of their abdominical cavities and genitalia. These are fungi unique to cicadas and usually make their tail ends drop off!
Lifecycle
There are three distinct stages in the lifecycle of a Cicada: egg, nymph and adult.
Egg Stage
After mating, the adult female Cicada will lay several hundred eggs. As she walks along the bark of a branch or plant stem, a slit will be made with the ovipositor (egg-laying spike at the tip of the abdomen) and about twelve eggs will be deposited into each slit. Further slits for more eggs will be made a few millimetres along and the process will continue until all the eggs have been laid.
Nymph Stage
The eggs remain in the slits for many weeks and then the eggs hatch into small, wingless cicada nymphs, which fall to the ground and seek shelter under the leaf litter.
Cicada nymphs search for cracks in the soil and burrow down between 100 and 400 mm, using their large forelegs. It is here, underground, that cicadas spend most of their lives — sometimes several years. Cicada nymphs feed by piercing plant roots with their needle-like rostrum and sucking up sap from a variety of plant species (from grasses to eucalypts). When the sap runs out, they tunnel around to find new roots from which to feed. While living and feeding underground, they continue growing, periodically shedding their skins.
Cicada exuviae and the hole from which it emerged September 2013
Adult Stage
When cicada nymphs finally reach full size, they dig their way to the soil surface with their front legs, which are specially adapted for the purpose. Cicada nymphs generally appear on the soil surface about nightfall from late spring or early summer. They then climb on to tree trunks or other elevated objects and shed their final skin. The fully-winged adult cicadas that emerge leave their old empty nymphal skin behind (cicada shells or exuviae).
Mature cicadas live for varying periods of time, from a few days to a couple of months, depending on the species. The majority live for around two to four weeks, during which time they mate and lay eggs, and the cycle begins again.
References
http://australianmuseum.net.au/Cicadas-Superfamily-Cicadoidea
http://www.australiangeographic.com.au/journal/cicadas-rhythm-of-life.htm
http://www.abc.net.au/science/articles/2001/02/17/2822486.htm
Karen Hising (Bushcare Officer)
