Are Perth’s flies getting worse? Yes – but they’re not nearly as bad as they could be

Western Australia’s top bug experts say this year’s fly season may be ramping up – but it’s still not a shadow on what our parents experienced back in the day.

November is typically the month WA experiences an influx of flies around the state due to high winds from the north and temperatures picking up as summer approaches.

Are Perth’s flies getting worse? You may be surprised. Credit: WAtoday

Last week’s humidity and rain created ideal conditions for fly larvae to hatch, which sparked an increase in the insect around Perth’s CBD and broader metropolitan area.

University of Western Australia entomology expert Dr Theo Evans said the influx kept with a broader historical trend.

“There were a few flies around last week because of those days that reached over 30,” he said.

Dr Darryl Hardie.Credit: Peter Maloney

“Their growth rate is massively accelerated [because of the temperatures].

“That’s really why we’ve had a bit of a peak in November generally every year.”

Dr Darryl Hardie, who recently retired from the Department of Primary Industries and Regional Development as their top entomology expert, agreed temperatures around Perth had reached a sweet spot in recent weeks for fly reproduction.

“Anything over 25 degrees is ideal for these flies to keep on breeding,” he said.

“If we get to 40 degrees, they’ll all disappear as they can’t survive in those sorts of temperatures and large numbers.”

However, Hardie said recent conditions also meant people were more likely to notice the increase in fly numbers.

“The weather has been up and down all spring, but [as it stabilises] people are getting outside, and are starting to notice,” he said.

“For example, my son’s visiting from Sydney, and he said to me, ‘Dad, gee, the flies are bad, aren’t they?’ – but he comes from an area where they don’t have many flies.

“It’s what happens when the fly population takes off after Christmas too down south – there’s more and more people down there, and they get irritated by the flies.”

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Evans said the current population was still nowhere near as bad as it was before the state government and biodiversity authorities introduced measures to cap the numbers.

“Compared to with what our grandparents used to experience back before the 1970s when the dung beetle population started to take off, fly populations are still nowhere near as bad as they were,” he said.

Hardie said while it was just getting started, the fly season ahead was slightly unpredictable.

“Don’t expect things this year to behave the same as they have done last year,” he said.

“But if you look up the fly population in Australia currently, it’s 40 times less than it used to be.

“We’re probably a bit more precious these days.”

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