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31/07/2017

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31/07/2017

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31/07/2017

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Hairy Cicada

Hairy Cicada (Photo by Alex Dudley)
Cicadas are insects. They are classified in the order Hemiptera, which includes all insects with piercing and sucking mouth-parts. Other insects in this order include bugs, aphids and scale insects.

There are just under 2000 species of cicada in the world, with 220 species identified from Australia, and just 8 in Tasmania. Yet among the Tasmanian species is one of the most ancient and unusual of all cicadas - the hairy cicada.

A Life Underground

Cicadas spend most of their life underground (nymph stage), with some large Australian species living underground feeding on the sap within the roots of plants for 6-7 years. Some North American cicadas spend up to 17 years underground.

When the nymph reaches full size it digs its way to the surface and climbs on to a tree trunk or other object and sheds its skin for the last time. The fully-winged adult cicada which emerges leaves its old empty nymphal skin behind.

In contrast to that of the nymph, the life of adult cicadas is very short, lasting only a few weeks. After mating, the adult female cicada lays its eggs by piercing plant stems with its ovipositor (egg-laying spike at the tip of the abdomen) and inserting the eggs into the slits it has made. The small, wingless nymphs that hatch fall to the ground and burrow below the surface, shedding their skin at intervals as they grow.

Tasmania's Ancient Cicada

Almost all cicadas belong to the one large Cicadidae family. The hairy cicadas, however, belong to the primitive cicada family Tettigarctidae, which consists of only two species.

The hairy cicada that occurs in Tasmania, Tettigarctia tomentosa, is endemic to the island, while T. crinita is found in the alpine regions of south-eastern New South Wales and Victoria. The habitat of the hairy cicada includes temperate rainforest, wet sclerophyll forest and subalpine snow gum woodland.

The hairy cicadas differ from true cicadas in features of the wing venation and head structure. They can also be distinguished by having eyes that are closer together than their individual diameter, as the above photo shows.

In contrast to other cicadas, which are notorious for their loud, piercing calls which can exceed 120 dB, hairy cicadas have greatly reduced sound producing organs and are incapable of producing audible song. It is believed that hairy cicadas communicate through the substrate. Both males and females communicate through the vibrations of a drum-like structure called a tymbal. This vibration is transmitted through the substrate below the adult and are detected by the sensory structures called empodia on all legs. This adaptation is not present in the Cicadidae.

Unlike other cicadas, adult hairy cicadas are active during the colder months of the year. The species has unique adaptations to the colder climate, such as the hairs that give the species its common name, and its dark colouration.