If the summer cicada chorus seems noisier than usual this year, that’s because it actually is – according to a Sydney plant scientist who spends his spare time studying the shrill invertebrates.
Dr Nathan Emery, of the Australian Botanic Garden in Mount Annan, says the 2017-18 cicada season in Sydney and the Illawarra is the loudest at least since 2013, when the last “mass emergence” of large species occurred.
“It’s true, it’s definitely the loudest season in a while,” he said.
“There are a number of larger species in particular that have come out in large numbers this year – they include the Razor Grinder, Red Eye, Double Drummer, Green Grocer and the Black Prince.”
Dr Emery said there was little research on what triggers the emergence of the memorably named insects from year to year, with study made difficult due to their intermittent emergence.
“There is anecdotal evidence to suggest they roughly spend about six to 10 years underground, depending on the species,” he said.
“And there was a reasonably good season back in 2010, which fits with the common idea of a seven year cycle.”
He also said a dry and warm winter, and March’s heavy rainfall may also have played a role.
Once cicadas have emerged from the ground and freed themselves from their exoskeleton, Dr Emery said they can live between one and four weeks. During this time their sole purpose is to find a mate – hence the frenzied noise.
But – just because cicadas are out and making themselves heard right now – doesn’t mean it will be quiet in a couple of weeks.
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“They employ a bet-hedging strategy, so individuals emerge over several months, just in case conditions decline,” Dr Emery said.
“But we’re starting to get towards the back end of the peak season.”
As for exactly how loud the male cicadas (only males make the shrill noise) can get as they “sing” to attract a mate, Dr Emery said their call could reach up to 120 decibels.
“The larger species tend to congregate and sing in a cicada chorus – and this is because it’s more attractive to female cicadas and a deterrent to predators, because birds can’t stand the noise,” he said. “The sound is about on par with an operating chainsaw, or a rock concert and it’s about 20 or 30 minutes of that exposure can be damaging to the human ear.”
According to the EPA, an increase of 10 dB is perceived as twice as loud.
Therefore an increase of 20 dB is four times as loud, an increase of 30 dB is eight times as loud, and so on.
Also, the addition of two identical noise levels will increase the dB level by about 3 dB.
For example, if one pneumatic drill is operating at 90 dB and then another identical drill starts operating next to it, the total dB level will be about 93 dB.
How loud is it at your place?
In a very unscientific experiment this week, the Mercury visited a couple of places we thought could be cicada hotspots to measure their sound with a smartphone decibel reader.
At Kembla Heights, near Harry Graham drive, the bush chorus averaged around the mid-70s, but peaked at 90 decibels at one point.
Surprisingly, standing in bushland at Mount Keira, it was much quieter than expected, with readings in the mid 50s on par with a quiet suburban street. Perhaps we just encountered a cicada lull at the time we were there?
Then, in residential Mount Ousley, we got readings in the mid-70s to 80s again.
We used an app called Decibel X, which was a free download to capture our decibel readings – but if you’ve got a real decibel reader that will give the most accurate results.
If you’d like to help map the noise levels, send us a reading and location from within the Illawarra and we’ll add it to the map.
Want to help with cicada research?
As research on cicadas is so scarce, Dr Emery has set up a citizen science project where people can contribute videos and sightings.
“It’s called the Great Cicada Blitz, and there’s also a smartphone app which allows people to record their observations of cicadas,” he said.
“We’re hoping to get a better idea of emergence and distribution patterns over the years.”
The scientist also has a field for fellow cicada enthusiasts, called Cicadas of Greater Sydney Region, which includes the Illawarra can help with species identification.
“They capture your imagination and interest like few other invertebrates – you hear them, you see their shells all over the trees and you just can’t escape them in summer,” he said.
“I think they’re a really fascinating way to reconnect people to the nature that’s in their backyard.”
- Australia is the cicada capital of the world with a predicted 700-1000 species. North America has around 170, South Africa around 150, and only 1 species in the UK. Only around 350 Australian cicada species have been scientifically described.
- A cicada begins its life as a nymph living underground in the soil and feeding off the sap from roots of a plant using a long proboscis (a feature of all sap-sucking bugs – Hemiptera).
- There is no concrete evidence that details exactly how long a cicada spends underground. Anecdotal evidence suggests it to be somewhere between 6-10 years, depending on the species.
- It was scientifically demonstrated in North America that cicadas can count seasons by detecting changes in xylem flow (plant root fluid).
- We don’t know what specific conditions trigger their emergence. Cicada nymphs do emerge in the warmer months, especially as overnight temperatures increase. A rainfall event prior to emergence is also important.
- Adults typically live for one to four weeks and feed on the sap of soft-wood branches. Their sole purpose is to find a mate.
- Males call to females in attempts to attract them, and the call-song is unique for each species. For larger species, such as the Green Grocer, Double Drummer, and Cherrynose, males sing in synchrony (termed a cicada chorus), and females will fly to the males. This calling strategy also deters predators due to the sheer volume of sound produced.
- The main predators of cicadas are birds, but also other invertebrates including spiders and robber flies.
- Cicada season in Sydney starts in September and can continue through to April/May. The noisiest months are November to January.
- The Hairy Cicada (Tettigarcta genus) – Australia’s oldest cicada genus that dates back to the Jurassic period – is incapable of singing. Males communicate through vibrating the substrate. Hairy cicadas also produce a thermal reaction to create heat that allows them to survive cold temperature in Victoria and Tasmania.
Source: Dr Nathan Emery, via the Royal Botanic Garden Sydney.