Flies! Damn flies! Everywhere in Australia, there are flies. Some areas have more than their fair share of annoying flies.
Sometimes it can be impossible to do anything outside without applying something to ward them off. This is because they are so persistent in trying to land on us. Unfortunately, all we can do is feebly adopt the Aussie salute to try and deter them from our face.
They were awful in Western Australia when we were at the northern end of the Wheatbelt last spring, just inland from Geraldton. When we tried to do some outdoor gardening work, they were relentless. Every time we ventured outside the caravan, we wore a fly net over our hats to keep them away from our faces and ears.
While there are about 30,000 species of fly in Australia, we only really encounter four types: the bush fly, house fly, blow fly and mosquito. However, it is the bush fly that is the persistent pest.
The reputation of the annoying bush fly (Musca vetustissima) has been around for a long time. Dirk Hartog in 1616 and William Dampier in 1699 both reported that bush flies were a massive pest. In the next century, Captain James Cook described them as horrendous.
Why are they so attracted to humans?
Bush flies love certain secretions in our skin. Our secretions contain sweat, proteins, carbohydrates, salts and sugars, which the flies seek. They use their very soft, fleshy mouth to suck up the secretions. They also love our dead skin.
It is not just humans they like to feed off. Flies play an essential role in the ecosystem as recyclers of nutrients from organic matter which plants can absorb and utilise. They are also critical pollinators of native plants and crops, and the predatory and parasitic species of flies help regulate the populations of other insects.
But why are there so many bush flies?
Before the development of agriculture in Australia, the bush fly’s major breeding sites were the faeces of humans, dogs, larger marsupials, and emus. Such droppings are small and are produced infrequently from the omnivores and carnivores. Nevertheless, around 150 bush flies have been bred from a human or dog stool.
After Governor Phillip arrived in Botany Bay in 1788 with five cows and two bulls, there was a dramatic increase in the supply of breeding material for the bush fly. Australian native dung beetles struggled to deal with sloppy cattle dung that became more numerous over time. Cattle droppings average two litres, and each beast defecates about 12 times a day. Today it is estimated there are 28.5 million cattle in the country. It means there are 33 million tonnes of dung across Australia every year.
Consequently, most cattle dung across the landscape remains unburied, providing the ideal breeding place for the native bush fly.
One cow pat can produce 2,000 to 3,000 flies which means billions are produced each year. To survive, the bush fly could breed in the dung of native animals, but cattle, sheep, horse, dog, and other introduced animals provide the ideal breeding conditions for them.
The adult female bush fly lays eggs in moist dung or manure. They can have up to 50 eggs in a batch – and up to 5 batches per female. These eggs hatch into maggots which feed on the dung. The maggots undergo three moults, pupating in the soil in a cylindrical brown cocoon. The pupa is drought resistant and can stay in the soil for a long time – even years. An adult emerges from the pupa only when conditions are right (temperature – 27.5 degrees C is perfect, moisture is required– especially from rain).
Following emergence from the pupa, adults take about three days to be sexually mature. Adults can go on to live for months if suitable conditions, namely sufficient moisture, protein and preferred temperature, are present.
Where do they live and breed?
In tropical Queensland, the Northern Territory and Western Australia, bush flies are found year-round. When the weather warms up, numbers increase, and they migrate further south. They can fly from central Australia into the southern states and across to Tasmania.
Why are they so hard to swat?
We invariably only achieve a very short respite as we wave our hands across our faces. When we get serious and produce a fly swatter, it only seems the bush fly is more attentive because they can evade our swatting.
Like all flies, this comes down to its design and ability to navigate the world — qualities that inspire the design of drones.
Flies have two sets of wings; one large lift-generating wings and a much smaller group of hind wings called halteres, which are sophisticated organs that enable the fly to balance and turn suddenly. I read how they work, but it is too complex for me to try and explain in layman’s terms. Instead, you can read for yourself here.
But in a nutshell, these halteres give bush flies the specific ability to evade swatting. They also have excellent peripheral vision, and they can determine light and shade very accurately.
Have you ever stood patiently waiting for that exact moment to swat a fly only to see it fly off afterwards? Peripheral vision and thousands of individual receptors allow bush flies to see someone’s hand coming to strike them in a way that humans can’t fathom or comprehend. The only success I have is using a long-handled swatter which has some success at beating the bush fly’s sophisticated warning system. But even then, my strike rate is not perfect.
Where do bush flies go at night?
They require polarised light to guide them visually. As the day turns to dusk, flies take refuge under leaves and branches, on twigs and tree trunks, on the stems of tall grass and other plants. They typically will not overnight on the ground.
But aren’t we breeding dung beetles to deal with the excessive cow pats?
The main problem is that while there are more than 500 species of native dung beetles in Australia, these beetles have evolved to process the coarse-textured, pellet-like droppings of native marsupials. The dung produced by cattle has very different properties. Only a few native dung beetle species can break up and bury cow pads.
A Hungarian entomologist, Dr Bornemissza, arrived in Australia in 1950. He was amazed to see huge amounts of unburied cow dung in paddocks, breeding flies. He suggested the importation of dung beetles from overseas to help control the number of bush flies.
In 1965, the Australian Meat Research Committee funded the Australian Dung Beetle Project. Bornemissza travelled to Hawaii, where dung beetles from Africa and Mexico were introduced to control horn flies. He chose seven species of dung beetles, and five of them were released in Townsville in 1967. Three species were successful, which led to further funding. From 1968 to 1970, cattle farmers across northern Australia took part in a program to release 275,000 beetles from four species, and three were successful. As a result, more species were introduced into southern Queensland and northern New South Wales.
The Dung Beetle Project ran until 1985. During this time, 55 species of dung beetle were imported into Australia from Hawaii, Africa and southern Europe. Two or three species of the introduced dung beetles are still active, and there are claims that the number of bush flies has dropped 90 per cent throughout Australia.
The establishment of exotic dung beetles in Australia has been considered a success. However, the project failed to establish dung beetles in all of Australia’s climatic zones. In 2014, a new species was introduced into Western Australia to try and fill some of these gaps.
A CSIRO entomologist believes dung beetles are “one of God’s gifts to us humans, particularly living here in Australia”.
However, a 2014 news report told of massive numbers of bush flies in outback Queensland, blaming the drought and less activity of dung beetles that hibernate during prolonged dry periods. This was only three years after 70 per cent of the state was underwater from flooding. But if dung beetles do go on strike in dry conditions, why were there still millions of bush flies near Geraldton last year immediately after a very wet and unusual winter in the southern half of Western Australia? They should have been in overdrive doing their stuff on the cowpats. In fact, I would argue that there are more bush flies today regardless of the weather than in the 1970s when I was growing up on Sydney’s eastern beaches outside all the time and fighting off flies during the summer months.
Could it be the introduced dung beetles have been losing the battle with cow dung since the end of the Dung Beetle Project?
Do you agree with the scientists who claim there are 90 per cent fewer bush flies today because of the work of the introduced dung beetles?