They're shedding their nymphal skins, sprouting their wings and desperately calling for a mate in the few weeks they will live above ground - the Blue Mountains is full of the chorus of the cicada.
There's been a mass emergence of thousands of the insects since the end of September especially around Wentworth Falls, Blackheath, Katoomba and in the Mid Mountains at Lawson, Hazelbrook and Woodford of the Cyclochila australasiae, also known as the Greengrocer variety - with the Yellow Monday and Masked Devil the most popular sightings of the species. It's a bumper crop not seen since 2013.
"You would certainly reckon it's in plague proportions around Wentworth Falls Lake, around Sinclair [Crescent]," said Professor David Emery, chair of Livestock Immunology at Sydney University's School of Veterinary Science.
The cycle of the cicada is suspected to run every seven years, "but they are also opportunists in one sense and if the conditions are just right out they all come," Dr Emery added. Their preferred temperature is 18 degrees.
Citizen scientists are helping shed more light on mass cicada emergence. (See https://www.inaturalist.org/observations/60912347). Birds eating the cicadas would be full right now, but Dr Emery doubts the theory cicadas are in a long multi-year cycle just to avoid predators.
This year's bumper crop has followed horrific bushfires and Dr Emery said a year after fires can also be good conditions for a mass cicada emergence.
"Quite a lot come out the year after a bushfire and that might be the sap flow out of regenerating bush with decent winter rainfall. We were predicting a good season and it's delivered."
"Katoomba and Blackheath haven't hit their full straps just yet, there will be a lot more emerging in the next little heat round."
"They are working [their way] down [the Mountains]. But the big emergence are in the more pristine bushland areas like the Upper Mountains."
Scientists in Australia had been mapping cicada emergence for about three decades to try and mark out a sequence, he said. Dr Emery predicts the next big emergence may be ine 2024 ( a smaller one) and a bigger crop in 2027
Most regions have about eight to 20 species, but some cicada species definitely have a preference for coast, forest or bush, based on available plant types - whether that's a She-oak/Casuarina for the Black Prince, the White Drummer on the coast with the Banskia and the Double Drummer "who love the tall timbers".
There are 1000 cicada species in Australia and less than half have been described, Dr Emery said.
The cicada "song" is produced by the male flexing his tymbal, an organ in its mostly hollow abdomen.
"They make a big song, try and get a mate and then die, it's pretty abrupt."
Aubrey Baker, 3, of Wentworth Falls, has been amazed by the sound and look of the recent additions to his landscape "but he doesn't like it when they climb on his clothes", Mum Casey Harris said.
See: Cicada names
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