The cicada life cycle

The female cicada

Not long after mating, the female cicada flies to a branch, twig or even the main trunk of a tree (depending on the species) and uses a long scythe-like device at the posterior ventral side of the abdomen known as an ovipositor to cut a groove into the plant tissue into which the eggs can be laid. She will then cut a number of grooves into the plant in a line, each packed with a number of eggs. The total number of eggs laid varies depending on the species, but can be up into the hundreds.

The Ovipositor of the female cicada

Preferences for oviposition sites vary depending on the species. Smaller species often prefer twigs or grass stems and may oviposit in either dead or living material depending on requirements. Larger species tend to oviposit in living branches or trunks.

Two to seven months after oviposition the nymphs emerge from the eggs and fall to the ground. After spending some time tunnelling through crevices underground they find a suitable space to excavate into a nymphal “home”. This consists of a small space in the ground beside a plant root, which can then be tapped into whenever required.

Cicadas spend the majority of their life as nymphs and moult a number of times in their underground residence until conditions become suitable for them to emerge and become adults. During this period some of the nymphs fall victim to parasites and entomogenous fungi. The exact duration that Australian cicadas remain underground as nymphs is unkown, with the exception of the Greengrocer (Cyclochila australasiae). It has been recorded to have a nymphal life cycle of about seven years.  The periodical cicadas of America are better known, with species having thirteen and seventeen year life cycles. It is possible that there may be large species with similar lengths of subterranean existence in Australia.  In contrast, it is likely that many of the smaller grass cicadas only spend one year underground.

Once the nymphs reach maturity and when the conditions are right, the nymphs emerge in large numbers and climb onto a clear vantage point, such as a tree trunk, stump or grass stem. This allows the adult stage to be able to pump haemolymph fluid into the wings without obstruction. Many of the moulting nymphs fall victim to predators, such as birds, as they moult from their nymphal skin. The final moulting process (to adult form) takes from 20-150 minutes giving ample opportunity for predators to strike. It still takes some time for the wings to harden once fully formed and it also takes a while for the newly moulted adults’ cuticle to attain true colour and provide camouflage (new adults are usually coloured yellow or greenish). All cicadas leave behind an exuvium of the final nymphal instar once successfully emerged. These exuviae are the classic “cicada shells” that become most conspicuous on tree trunks and posts during the warmer months.

The length of time that adult cicadas survive varies depending on the species. Grass cicadas may only last 1-2 weeks. Large cicadas may live up to four months in extreme cases.

For further information refer to Moulds (1990).

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