Lack of dung beetles to clean up livestock droppings causes worst fly season WA has seen in 40 years

WA is in the grip of one of the worst fly outbreaks in living memory, thanks to an unusually long and wet winter that has created the perfect breeding ground for the pesky insects.

Perth and the South West can expect the infestation to get progressively worse in the coming weeks as northerly and easterly winds blow billions of flies away from their breeding grounds in the livestock-rich Mid-West.

Late spring and early summer have always been peak fly season, but this year has been particularly bad due to the rain-soaked last few months.

Heavy rains produced more green fodder for livestock, whose moist droppings are an excellent food source and breeding ground for flies and other insects.

The monster larva population was able to develop undisturbed because the weather was too cold for the dung beetles to clear the State’s pastures and shrubs.

Insects reduce the country’s fertilizer load in two ways. First, young insects voraciously eat animal feces as they transition from larva to insect. Second, adult insects dig tunnels and haul dung up to one meter underground, depositing it for food and reproduction.

Associate Professor Theo Evans, from the University of WA’s School of Biological Sciences, said this time of year was the Goldilocks period for flies.

“When the temperature consistently drops below 15°C, the fly population dies,” he said.

“You can pretty much draw a line across the state from Geraldton to Esperance and the flies won’t survive the winter in that southern area, but in the spring it’s a different story.

“Currently the air temperature is high enough for the flies to grow, but the soil temperature is still quite low.

“Dung beetle species that are active in the summer in WA will not emerge to the surface until the soil warms, and animal poop will remain where it is until this happens.

“Active dung beetle species and rain reduce manure in winter, but at this time of year it just sits there and sustains the fly population.

“Like every year, the summer bugs won’t come out to help until the end of December.

“The difference this year is we’ve had a pretty wet winter compared to recent decades. It was the kind of winter we had in Perth 40 years ago, and now we’re seeing the kind of fly population we had 40 years ago.”

“This is a shock to people who can’t remember what it was like to live in Western Australia until the 1980s.

“Wet, sloppy poop created by moist green bait is why flies are now driving people crazy.”

Brush flies evolved in Australia when livestock were imported from England because native dung beetles were conditioned to work by dropping animals such as kangaroos into dry, ball-like forms.

Several dozen new species of scarabs were introduced between 1968 and 1985 under a program managed by the CSIRO.

Of the 55 insect species reared in CSIRO laboratories, 43 were released and 23 survived and spread across the country.

Associate Professor Evans said there may be relief in sight.

“We are tracking new insect species that have been released relatively recently and are active in the spring,” he said.

The first spring bugs were released five years ago and the most recent release of the spring-loaded “manure roller” was between Pinjarra and Gingin last year.

“We hope that by the end of the decade, scarab activity will emerge in the period we are in now,” Associate Professor Evans said.

“Winter beetles disappear around September and summer beetles don’t appear until closer to Christmas, so this time of year is a dead zone for dung beetles but warm enough for flies. It’s a gap in coverage that we hope to close over the next few years (October, November and December).”

Scientists hope spring bugs can withstand pressure from a species that emerged decades ago and turned out to be a fertilizer thieve.

“They didn’t realize it at the time, but this particular species in the Mediterranean may have been stealing fertilizer that other insects had pulled underground,” he said.

“Parent insects, usually the mother, usually guard the dung as the larvae grow, but this is not always the case.”

Associate Professor Evans explained why holidaymakers in the South West can expect to be hassled at the beach at Christmas.

“Strong easterly and northerly winds this time of year blow flies southwestward from the warmer parts of the state,” he said.

“Flies aren’t the smartest animals, but they realized that if they got into that big blue area at the edge of the land they would die, so when they got to the beach they bent down and stayed there.

“Since there is no fresh water on the beach, they look for whatever moisture they can find, and this usually happens in people’s eyes, ears and nose.

“When we go to the beach they see us as a living body of water, and warm weather means they are particularly active because their wing muscles are more efficient above 25C.”