If you have ever walked through the Australian bush on a hot summer's day, ears ringing from a pulsing crescendo of calls – and the disconcerting feeling of water droplets raining down – chances are you have experienced a cicada season in full swing.
The insects' buzzing call is a familiar summer song, and some years it hits greater heights than others.
Residents in coastal northern New South Wales are reporting the cicada chorus is louder this summer than it's been for a while, and that notorious "cicada rain" — otherwise known as urine from these big-drinking insects — is being felt along with it.
Bowraville's Alar Hordern does outdoor property maintenance and said it has been hard to escape the wave of chirping noise.
"Every day out at work they're still loud, even with noise cancelling headphones on," he said.
"I think the last loud year like this was 2016 or 2017."
Mr Hordern isn't alone in his observations.
Southern Cross University professor of entomology Nigel Andrew said the right mix of weather conditions this year had led to a boom in cicada populations.
He said that because cicadas could live underground as nymphs for six to seven years, they could be much more abundant in some seasons than others, with peaks occurring every few years.
"It seems the conditions are just right [this year] — there's been a fairly mild winter, with a warm summer, with a bit of rain around," Professor Andrew said.
"So, this has been one of the years they have successfully been able to breed up and move from being underground over winter, where they have been feeding on tree roots, and being able to emerge and start singing ready for Christmas."
He said the cicadas were accessing enough nutrients underground so that when they emerged, they had enough energy for their final metamorphosis into an adult.
'Deafening' courtship chorus
The cicadas' call is all about the males trying to attract a female, and their courtship song increases in intensity as they compete with each other.
They are known as the loudest insect in the world, and their sound in decibels can be as loud as a rock concert.
"It can be particularly deafening when there's thousands of them around," Professor Andrew said.
"They can get up to about 120 decibels, so they are well and truly over and above a lot of noise restrictions.
"When it gets quite hot, they get that pulsating event of the noise coming through," he said.
"The females respond to more noise … that's what they are attracted too, so the males try to pump out a stronger noise and also to get over a lot of the other calls in the local area as well."
Professor Andrew said the "razor grinder" cicada has one of the loudest calls.
"When chorused, they can be deafening," he said.
"The name refers to its harsh call, which has been likened to the sound of a metal grinder."
Amanda Gray, who lives in King Creek, just west of Port Macquarie, said cicadas — including razor grinders and "cherry noses" —were causing her family's "ears to buzz".
"In the bush they collectively reach a crescendo then ease off for a second before starting again and slowly growing louder. It's like a cicada wave," she said.
"We are loving it, however, the only downside is that they drown out the birdsong ... when we moved here this time last year, there was no cicada noise."
Bumper season for summer insects
Professor Andrew said cicada numbers are strong around his home in Goonellabah, on the outskirts of Lismore, and that other summer insects are also experiencing a bumper season.
"There are lots of Christmas beetles around … so there's been a lot of classic Australian summer insects rearing their heads this year, which is really exciting," he said.
"There have been so many years where it has been so quiet."
Detailed data on numbers season to season is hard to come by, Professor Andrew said.
"We don't have good data on abundances, or where the different insects are being found and how frequently they've been found," he said.
"One of the first few things that's been done from two to three years ago ... is to get a count of Christmas beetles in different areas, to identify if they are as common as they have been, or are their numbers increasing as we are moving forward."