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The fly in your eye


By Jim Heath

Drawings and cartoons by Janet Baxter

Here's a copy of my book about Australian bush flies and dung beetles -- the original text, drawings and cartoons (published 1989). It was a best-seller (in Australian numbers).

If questions like the following have been making your nights hell, you've come to the right place:

Why bush flies pester you.
How to keep flies out of your home.
What the dung beetles are doing.
Why flies come at certain times of the year.
How long flies live.
An easy way to tell bush flies from house flies.
What blow flies are good for.
The extraordinary way that flies taste things.
What's impressive about a fly brain.
How bush flies came to Australia.
Practical results of CSIRO research.
Bush flies: are they doomed?

© 1989 Viacorp. All rights reserved.
ISBN 0 646 01042 5


Before we start...

  1. This document is copyright, but you can make any 'fair use' of it under copyright law. So it's OK to use it in school projects, for example, if you say where you got it. But 'fair use' of course doesn't include poor-attitude things like re-publishing the work (or parts of it) and claiming it's yours, or copying it to another website, or putting parts of it in some other document or website and implying you wrote those parts, or using any of it in a publication that you sell. You get the idea.

  2. At the end of the book you'll find thanks to the 'CSIRO'. If you don't know Australia: that means Commonwealth Scientific and Industrial Research Organisation. Thousands of scientists, every kind of research... including flies.

  3. Small print: It would not be prudent for me to give guarantees about the information and advice in this document. So the information and advice is offered without any responsibility or liability on any account whatsoever on the part of the author or copyright holder.


Main sections

Bush flies!
Dung beetles vs bush flies!
Other kinds of flies
Update, links, and more by the same author
Eye protection, fly repellents, special hats, nets

Bush flies!

Why they pester you

The female bush flies pester you most. They want protein. They need it to develop their ovaries, to prepare eggs for the next generation of bush flies.

They get protein from your tears, saliva, the mucus in your nose -- and from blood, if you have any fresh cuts.

To be blunt, they are also hoping you might do a poo. Bush flies are programmed to stay around animals, because animal dung is their favourite place to lay eggs.

Sometimes they drink sweat. It hasn't got much protein in it -- not nearly enough. But it's useful if the flies are thirsty, and it has some minerals they can use.

Male bush flies probably hang around you mostly to be near the females! They don't need much protein.

When bush flies swarm around you, there are usually about three females for every male.

Entomologists have carried out many experiments to study the female bush-fly's need for protein. For example, if female flies are fed only sugar and water, they live a normal lifespan, but produce no eggs. They can be deprived of protein for about two weeks without affecting their fertility. After that, fertility starts to decline. By the end of five weeks without protein, the flies are infertile.

So the urge in a female bush fly to find protein is very strong. They can find an animal in seconds if it's upwind. They also fly immediately to fresh dung: if you scrape off the crusty surface of an old cow pad, any flies around seem to appear instantly.


Why the small bush flies pester you more

The smaller the female bush fly, the more she needs extra protein to produce her eggs. The small bush flies are short of protein because they've grown from larvae that haven't been able to get enough food. This happens if there are too many larvae competing for the food, or if the food quality is poor.

This is why the smallest flies are so frantic and persistent. They're desperate, protein-hungry females. They want that protein in your tears, in your nose, in your saliva.

And note this: even if little flies get all the protein they want, they don't grow bigger. They can't. They have exterior skeletons and stay the same size all their lives.

So there aren't different types of bush fly. Just different sizes. Fat ones that don't bother you too much. And little ones that act like demons.


Where they come from -- or damn those cows!

When the first colonists came ashore in 1788, they brought ashore five cows and two bulls. The bush flies watching the scene must have felt a dawning sense of unbelievable good luck.

These days, most bush flies breed in cow dung. They breed there because there's so much cow dung, and because there's been nothing to stop the fly breeding -- or slow it down.

There are more than twenty million cattle in Australia. They each drop around 12 'pads' a day. And from each cow pad, up to 2000 flies can emerge. (Mathematical readers might like to calculate whether there are more stars in our galaxy, or more bush flies bred each year in Australian cow dung.)

Before the cows arrived in Australia, the bush flies had a harder time. They bred in animal dung, but there were snags: kangaroos and other native animals didn't produce much dung per hectare, and the dung dried out quickly because it was small. So the flies had poor breeding material, and not much of it.

Bad luck for the flies.

But then the cows came and soon there was plenty of dung. Huge, splashy cow pads. And there was nothing much to stop flies breeding in it. In some parts of Australia, a few types of native Australian dung beetles moved into cow pads and bred there. These beetles cut down fly breeding by breaking up the pads and burying them. For example, the Onthophagus ferox in Western Australia, and Onthophagus granulatus and Onthophagus australis in south-east Australia. They were some help in reducing fly breeding. But not nearly enough.

Meanwhile, the cow pads caused another problem: each pad covers a bit of pasture. If the dung beetles aren't active enough to break up the pads and bury them, the pads dry out and stop new grass from growing. (Except rank grass, which the cattle won't eat.) The old, dried-out pads can last for years. And they add up to a big area: new pads can make 5 to 10 percent of a pasture worthless each year.


How the bush flies get into the cities

In the winter, bush flies die out in the southern part of Australia. It's too wet and cold.

But they keep breeding in the warmer north and the drier inland. The population rises and falls with rainfall and temperature.

From August to November, warm winds blow from the north. (Pretty regularly, about twice a month.) These winds lift clouds of pregnant female bush flies and carry them south. The flies come south in steps, in jumps -- sometimes hundreds of kilometres a day.

And they don't get blown back when the wind shifts to the north. The wind acts like a one-way valve: when the wind blows from the south, it's too cold for the flies to get airborne. They stay where they are. They wait for the next warm wind coming from the north.

As the flies come south, they find winter pasture covered with good-quality cow dung. The females start laying eggs, just as the air temperature is warming up fast. It's the new-bred flies from these rich breeding grounds that swarm into our southern cities.

In the east of Australia, flies start crossing the Queensland border in August. They reach Canberra in about the middle of September. By October they've reached Victoria. Sometimes they get as far as Tasmania (by December).

In the west, migration from the north-east starts in early October. By the end of October, they're everywhere in the south-west.

Bush flies are also blown out to sea. There are records of ships at sea being invaded by bush flies. (The 'Thalla Dan', to mention one case. It was invaded by flies when it was 30 km from Fremantle.) Most entomologists accept that winds blow bush flies 230 km across water to Tasmania. If the winds fail, the flies drown and become fish food.

In the southern pasture-lands, the breeding mathematics of the fly invaders are awesome. The females from the north are fat and laden with eggs. (About 55 eggs per female.) The survival rate for the eggs in the spring-pasture dung is about 30%. (The green shoots in the pastures have hardened and the cattle have produced dung with a fine fibrous structure.) Under these conditions, the immigrant flies produce about ten times their number. The new generation of flies themselves breed within a few days, and multiply their numbers again by ten. This can go on for several weeks. Ten times ten times ten times... No wonder we notice a 'sudden' fly problem.

Later, in the summer, things reverse and the fly-population numbers decline fast. The pastures dry, the cows produce dung that's coarsely fibrous, and the flies bred from it are less fertile. Each female only lays about 18 eggs, and only 1% of the eggs survive in the dry summer weather. 1000 females produce only about 18 offspring. The same applies to the next generation. So the bush flies almost disappear.

But the flies pester me here in the desert. And there aren't any cows!

There are no bush flies in the southernmost parts of Australia in the winter. As I said, it's too wet and cold, and they all die off. But in other parts of Australia, there are always bush flies around. You'll find them in the central deserts, by the sea shores, on the tops of the mountains, and on the larger inshore islands.

And contrary to what you might think, the arid parts of central Australia actually support a lot of cattle. And of course bush flies breed in other kinds of dung too.

The main point about pesky flies in the desert is this: there may be fewer flies there, but there are fewer people too. It's the balance between numbers of flies and numbers of targets that matters. Flies from all around will swarm to you and ignore the rocks, sands, dry shrubs and other beauties of the countryside.

The behaviour of the bush flies make them a pest. Not their numbers per hectare.


When to expect them

Sydney

Bush flies blow in from the pasture-land breeding areas on hot westerly winds. This means the bush-fly population in Sydney is erratic, because the winds are. Now you see bush flies, now you don't.

There are very few bush flies until October. The waves of flies grow denser and denser during November and December. The peak comes in January. The numbers then drop slowly until the end of March -- and then the bush-fly season is over.

The only sample data CSIRO has is for 1963-64. (It was gathered by a manufacturer of veterinary products and insecticides. They counted flies at eight sites around Sydney and passed the information on to CSIRO.) During the year, they caught 1,024,277 flies! Of these, 39,861 were bush flies, and most were caught in January (21,430).

If you look at these averages, only one fly in 48 is a bush fly. But the bush flies are pesky and come in waves -- so they can be a serious nuisance.

The data also show that bush flies only start appearing when the maximum day temperature reaches about 18oC. Then there's a lag, until the average temperature rises above 18oC -- and breeding in pasture-land really starts taking off.


Melbourne

Bush flies appear as early as September, with the numbers increasing through October and November. The peak is in December or January.

The house-fly population rises in about the same pattern.

The Victorian Fly Suppression Unit describes the problem as follows:

"The bush fly has been identified as the primary outdoor pest, especially at social functions, sporting activities and other pursuits in open areas. It occurs around homes in the outer suburban areas each summer and can also be a problem in the inner suburbs and the city itself in certain 'plague' years. House flies, stable flies and blow flies are secondary problems in and around homes, particularly at backyard barbeques or other outdoor leisure activities. Unlike bush flies they usually do not travel far from their breeding source and large numbers can generally be traced to neglected plant or animal waste in the near vicinity."

"The Fly Suppression Unit has confirmed that the bush fly does not breed in the metropolitan area but is blown in from farming areas. Its main breeding source is cattle dung and during summer breeding takes place throughout pastoral areas of Victoria. In winter, the fly dies out in Victoria, but each spring returns from States to the north of us, carried on the northerly winds."

Adelaide

No one has counted bush flies here, or seems to worry about them much. The reason: they're only a problem now and then, when they come in on a hot northerly wind.

Perth

Bush flies are first noticeable in October. The numbers rise steeply in November. They peak in December (when people and food can be covered with bush flies at December barbecues).

After the peak, the numbers fall off fast. By the end of January, almost all the bush flies are gone. (This sharp peak and sharp drop-off only happens in the south-west of Australia. In the south-east, the bush flies linger until March.)

The pattern in Perth is very regular. To the north-east, there's a large amount of agricultural land with a climate where bush flies survive the winter and breed all year, with the breeding rate depending on the temperature. By September, breeding increases rapidly because of higher temperatures and drier weather. Temperatures are also high enough for large numbers of pregnant female flies to move south-west on north-easterly winds. They then breed in the rich cow dung in the southern pasture-lands.

Rising temperatures during October and November hatch out the young flies and these breed in the same southern pastures. A kind of chain-reaction takes place, and the bush-fly population rises to a characteristically sharp peak in December.

By the end of December, the dung quality declines because hot, dry weather dries out the pastures. Breeding slows down, and the survival rate of larvae also drops sharply. By the end of January, it's all over: near the coast, where most of the people live, there are hardly any more bush flies.

Brisbane

There isn't much of a bush-fly problem here. The pasture-lands around Brisbane are poor for breeding in the summer because it's too wet. A few bush flies come in on the wind, but these strays aren't a great nuisance.

Canberra

Some bush flies start appearing in October and November, but they aren't usually a problem until December. Then they reach a peak, and the numbers only decline very slowly. There are still bush flies around in March. Only in April are they really gone.

The tableland around Canberra is only marginal for bush-fly survival. They don't start breeding there until the beginning of December, and by then the quality of pastures and cattle dung has started to decline. This makes the breeding areas around Canberra one of the good targets for dung beetles -- but more on this later...

Alice Springs

Bush flies are always around, but not normally in great numbers. The fly population normally rises quickly after heavy rainfall. The rain first causes a spurt in plant growth, and this leads to better-quality animal dung. The flies breed fast in the dung, then spread out looking for other good breeding sites. But if the weather remains dry, in a month or two the fly numbers are back to their average (low) figure.

Though there aren't great numbers of bush flies in Alice Springs (compared to Perth in December), they tend to be small, persistent and very annoying. Also, there's the 'desert effect' we mentioned earlier: there may not be many flies, but there aren't too many targets for them either. Any targets there are (visitors to Alice, for example) can get pestered a great deal.

Tasmania

Unpredictable. Sometimes Tasmania gets no bush flies at all for several years. When they appear, it's only in the warmer months.

Subtropical areas

Bush flies are active in the northern subtropics all year round. After the summer rains start, the numbers build up to a peak in autumn. The numbers usually stay high over winter, but then drop quickly during spring.

In the drier tropical areas, especially the north-west, the main build-up comes in late autumn and early winter. There's a rapid decline during spring and there are hardly any flies at all during the summer 'wet'.


Temperature and other things that affect how many flies pester you

Yesterday the bush flies were all over you, up your nose, in your eyes. But today it's all quiet. Nothing. Hardly a fly in sight. Why?

No one has a final answer to some of these mysteries -- what you might call Fly Psychology, or the Crowd Behaviour of Bush flies. But some of the factors have been studied closely, and give some interesting clues:

Temperature. Below 12oC, bush flies don't fly. They usually keep still, and prefer warm surfaces. (If you notice some that have been still a long time, they might be dead: low temperatures can kill them.)

When the temperature goes up just a bit -- to about 12.5oC -- some of them fly again. But only short flights. As the temperature rises, they get more and more active, and bother you more and more. At 27.5oC they're at their worst.

At higher temperatures, they fly less, and pester you less. And at 35oC, they head for the shade, like the rest of us. They just sit in the trees, or maybe inside a house (the only time they are likely to go inside).

Humidity. This hardly affects them at all. It doesn't matter much whether it's a sticky, humid day, or a very dry one. (Provided everything else is the same -- temperature, and so on -- and assuming the flies aren't thirsty.) I mention this because some people have the theory that flies get more annoying on dry days. If so, it's not the humidity itself that's directly affecting their behaviour. But low humidity can have an indirect effect: if you notice more pesky flies on dry days, it may just mean they're thirsty and want a drink from your eyes.

Wind speed. Another surprising one: strong winds don't make bush flies less pesky. They bother you almost as much on a windy day as on a still one. Winds speeds of 36 km/hr and more were common in one set of experiments, but it didn't keep the flies grounded -- or off people. But note this: though bush flies take to the air on a windy day, they get blown downwind. Relative to the air, they fly pretty slowly (about 8 km/hr, top speed).

Solar radiation. Bush flies get more active as the solar radiation increases. (This means the total radiant energy hitting the fly -- from the sun, reflected from clouds, etc.) So if the air temperature and everything else is the same, flies are more of a nuisance the more solar radiation there is.

But solar radiation only affects fly activity about one-sixth as much as temperature does. (Technically: using an additive regression relationship between weather variables and logarithms of fly catches.) For one thing, this means bush flies slow down around sunset -- even if the temperature is their favourite 27.5oC.


How fly experts get their information

You may have wondered about the figures from Sydney: someone caught a million flies (how?) and carefully picked out the bush flies?

Sounds like a lot of work. Actually it's worse than you think. Most of the flies were caught in baited fly traps, and the research people followed these instructions for a sample of flies from each batch (and I quote):

1. Note the time, weather conditions, the temperature and what bait you are using.

2. Keep the females alive in tubes until you can dissect them. If it will be more than a day, put the flies in a fridge -- or pickle them in alcohol, glycerine and water (proportions: 7:1:2).

3. Kill any live flies in alcohol, then dissect all flies under 0.8 saline.

4. Pin flies ventral side upwards. Measure the width across their eyes. Open abdomen of females and remove ovaries. Note if pregnant or not.

5. Remove spermathecae and squash under the coverslip on the microscope slide. Check contents for mass of sperm tails.

6. Keep the following records for each fly: sex, headwidth, and (if female) whether pregnant or not, fertilised or not.


Bush flies in the old days

"The flies are at you all day, crawling into your eyes, up your nostrils and down your throat... and no sooner do they, from sheer exhaustion, or the loss of daylight, give up the attack, than they are relieved by the mosquitoes."

- Lieutenant John Lort Stokes, R.N.,

March 1838

Lieutenant Stokes was First Mate on the "Beagle" and his Australian bush-fly experience was typical. We hear similar complaints from:

  • D. de Prado about the Torres Strait Islands in 1606.

  • F. Pelsaert about Geraldton, Western Australia in 1629.

  • W. Dampier about the North-West of Western Australia in 1688 and 1699.

  • de Vlamingh about the Swan River of Western Australia in 1697.

  • J. Gonzal about the Gulf of Carpentaria in 1756.

  • M. Flinders, with more bad news from the Gulf of Carpentaria in 1802.

  • G. Grey, who confirmed that flies were still bad in the North-West of Western Australia in 1837.

  • C. Sturt, about Cooper's Creek and west of the Darling River in 1845.

  • Cleland, who wrote about pesky bush flies in the country around Sydney and Adelaide in 1913.

  • Johnson and Bancroft, who reported in 1920 that bush flies were a nuisance in Perth and Melbourne streets.

Not to forget Australia's famous explorer Ernest Giles, who wrote in his field book in 23 April 1876: "The flies at the camp today were, if possible, even more numerous than before. They infest the whole air; they seem to be circumambient; we can't help eating, drinking, and breathing flies; they go down our throats in spite of our teeth, and we wear them all over our bodies; they creep up one's clothes and die, and others go after them to see what they die of. The instant I inhale a fly it acts as an emetic. And if Nature abhors a vacuum, she, or at least my nature, abhors these wretches more, for the moment I swallow one a vacuum is instantly produced. Their bodies are full of poisonous matter, and they have a most disgusting flavour, though they taste sweet. They also cause great pains and discomfort to our eyes, which are always full of them."

The only historical figure who seemed to miss the bush flies was Captain Cook. And he was paying attention because he had skilled insect collectors with him on the "Endeavour". Probably he was just lucky, and came during a dry season when the fly numbers were very low.

The first person to describe the bush fly scientifically was F. Walker in 1849. The fly even carries his name: Musca vetustissima Walker.

But to go way back, as far as possible: most entomologists agree that the bush fly didn't evolve here. It came in, much as it is today -- probably by island-hopping in from the North. When this happened, nobody knows. But it's likely the fly got to Australia in an Aboriginal boat, the same way the dingo got here. In that case, the bush fly might have arrived in Australia as long as 45,000 years ago.

The first bush flies in Australia found no cows, of course. But they bred easily in kangaroo and emu dung -- and maybe in dingo dung (if there were any dingos).

They also bred in human stools. Up to 150 flies can emerge from a single human stool. (As some modern tourist-scientists have confirmed, when they've examined unburied human stools in the bush near coastal holiday resorts in New South Wales.)

But as I said, the big trouble started in 1788, when the first English colonists brought ashore five cows, two bulls, seven horses and 44 sheep.


Life cycle of the bush fly (including their record-breaking sex life)

When a male and female bush fly mate, they stay joined for an average of 1 hour and 20 minutes. (In the lab, when they aren't disturbed.) This may not be up to the standards for mating Rhinoceroses (3 hours!), but it's not bad for a small insect.

In this marathon, enough sperm gets transferred for two batches of eggs. Later the female can mate again -- and sometimes once more after that. Some heroic females might lay up to five batches of eggs.

Once a female bush fly is loaded with fertilised eggs, she looks for dung to lay them in. (Bush flies don't lay eggs in rotting meat, by the way.)

When she finds dung that's fresh enough, she first feeds on it. Then she walks all over it, exploring all its little caves and cracks, not forgetting choice sites below overhanging edges. If she's satisfied with what she finds, she backs into a crevice (or sometimes under the edge of the dung) and starts laying eggs. They come out about one a minute and get partly embedded into the surface of the dung. She usually lays the whole batch in the same place. The result: anywhere from 5 to 50 eggs, all cemented together in a mass.

Bush fly eggs are creamy-white, elongated and slightly curved. One end is more pointed than the other. An average egg measures 1.8 mm x 0.35 mm -- small, but not microscopic.

Another technical point: lots of things about bush-fly breeding follow simple linear mathematics. For example, the number of eggs per batch varies linearly with the size of the bush fly (measured by headwidth). Other things being equal, bigger flies produce more eggs per batch than smaller ones. So if you plot eggs/batch against the size of the flies, you get nearly a straight line.

The rate at which the eggs develop also varies linearly: but the development rate depends on temperature, not on the size of the fly that laid the eggs. As you'd expect, eggs take longer to hatch at low temperature than at higher temperatures. (See the little graph.)

The eggs hatch out maggots very quickly in hot weather: it takes only 5 hours at 39o C. (Compared, for example, to 17 hours at 21o C.)

The maggots immediately dig into the dung. The maggots -- or to be more technical 'larvae' - have mouths constructed for eating moist dung. They munch blindly at soft, undigested plant and animal tissues in the dung. They also drink a liquid mixture of bacteria and digested food.

They meet two problems. First they need moisture. Second they need air. Both of these aren't always easy to get in a cow pad that's drying out. To keep moist, the maggots have to keep going deeper into the pad. But this means air becomes a problem.

What usually happens is that as the cow pad dries, the wet parts inside shrink away from the crust and an air space forms under the crust. At first the maggots feed on this wet inner surface. Then as this shrinks, they dig into it. But they keep backing up in their tunnels to expose their backsides to the air gap under the crust. In pads that have been drying for awhile, the maggots are often huddled in the centre of the pad, near the bottom.

When the maggots are fully grown, they leave the pad. They always do this between midnight and dawn. (How they know the time is a mystery.) A few leave the first night. A much larger number leave the second night (also between midnight and dawn.) And the final wave gets out on the third night.

If you're picturing scientists with flasks of coffee and torches, staying up all night in desolate fields -- forget it. This knowledge about 'larval emergence' was gathered by P.M. Greenham for a Ph.D. thesis, and he built an automatic device to count the larvae (maggots). He suspended some maggot-infested cow pads over a big funnel. Below the funnel was a kind of circular tray with containers around the edge. A motor rotated the tray once a day, so every hour there was a different container beneath the funnel. So it was only necessary to visit the maggoty cow pads once a day and count how many maggots had dropped into each container.

The maggots that emerge from the pad are the lucky ones. Under some conditions, few maggots live that long. For example, in a cow pad kept at 14o C, only about 20 per cent of the maggots survive. This compares to 80 per cent at 21o C. And at temperatures below 12o C, no maggots survive. At higher temperatures, the maggots may develop normally, but they die at the pupa stage. At 46o C, for example, the maggots pupate normally, but no flies appear.

Similarly, if the cow pads are too wet or too dry, fewer maggots survive. In one experiment, 20 per cent of the maggots were killed simply by spraying their pad lightly with water every day.

Finally, there is often competition for the dung. If there are too many maggots in a pad, a smaller percentage survive than in a pad where there's plenty of dung for all. And of course there's the whole question of competition by other species -- especially dung beetles. But that topic I talk about later.

When a maggot leaves the pad, it digs into the soil nearby. It stops feeding and grows a hard barrel-shaped enclosure -- the 'puparium.' There it stays, while it turns into a kind of genetic mush -- that miraculously rearranges itself into a fly.

This change can take anywhere between 3 days and 18 days. It depends on the temperature. If the soil is at around 18o C, the pupa stage lasts about 18 days. On the other hand, if the soil is very warm -- 39o C, for example -- the flies come out of the puparia in just three days.

As you might guess, the rate of development in the puparium varies linearly with temperature. (Pretty accurately true between 16o C and 29o C.)

But survival rates are a different story: they are very sensitive to temperature and don't follow a linear rule. 80 percent of pupae survive at 38o C, but none survive at 41o C. Survival also drops to zero when temperature gets too low: none survive at temperatures of 14o C or lower.

Wet soil also cuts their survival rates. In one experiment, no flies came out of puparia when the soil had a moisture content (by weight) of 25%. The best survival rates in this soil were with a moisture content between 8% and 14%. At a 4% moisture content, survival rates again began to drop.

When the flies break out of their puparia and struggle to the surface of the soil, they are full-grown. They may be small bush flies, or large ones -- but their size is fixed. If they are big, and female, they may bear many batches of eggs. If they are smaller females, they'll be less fertile.

From egg to fly, all this has taken just a few weeks. In warm weather, about two weeks. In cold weather, up to ten weeks.

Neither male nor female is sexually mature when it comes from the puparium. But it doesn't take long. If the days aren't too hot, or too cold, new-born bush flies can be mating with each other in just three days.


Bush-fly habits and flight performance

One of the easiest ways to recognise species of flies is by watching how they behave and what they eat.

For example, house flies and bush flies look similar, but they don't act the same way. Bush flies rarely go indoors, and when they do, they immediately gather at windows to try to get out. But house flies -- as their name warns -- like to be in houses and buildings. They don't like pastures and the outdoor life.

And there's another thing: bush flies swarm around you and try to get at your eyes. House flies don't do this (just as well too, germ-buckets that they are).

So if a fly is pestering you, it's probably a bush fly. And once a bush fly finds you, it will hang around you for hours... unless -- as I hinted -- you go inside a building, or into some other dark place. They don't like shady places like forests. One easy way to shake off a cloud of bush flies is to retreat into some shrubbery.



This might also give a clue about why the old-fashioned cork hats work. To get at your face, the bush flies have to go inside something (the line of corks). Their genes rebel at this. They're programmed to stay outside, in pastures, and zero in on animals.

Running hot and cold

As I mentioned earlier, there's one time bush flies will go inside, or seek shady places: when it's too hot! If the temperature goes above 35o C, that's what they do. They head for shade.

They also slow down when the temperature gets too low. At around 12o C, they can't fly. They just walk -- and slowly. If they walk to a warm spot in the sun, they sometimes take to the air again. But then they quickly slow down as the air cools them. You can actually hear them slow down, their buzz getting deeper like a toy winding down. Sometimes they fall out of the air like they've been shot.

During the day, bush flies speed up and slow down as the temperature rises and falls.

Any minutes or hours that a bush fly spends at temperatures below 12o C shortens the fly's life. For bush flies, low temperatures are like lead poisoning. It adds up.

And frost kills them straightaway.

Airborne slow-pokes

Bush flies can't fly more than about 8 km/hr -- a fast walking speed. They also fly low.

Their pokey flight speed means that wind can easily blow them away. This can be useful, if you can get the wind to catch them as they hover near you.

But the problem is that the wind can also blow new flies in your direction. As I said, that's exactly how they get into the cities: on the wind, passively. They can't make any progress against a wind of any strength, so the wind takes them whichever way it blows.

Who has seen the wind?
Neither you nor I:
But when the flies blow into town
The wind is passing by.

(With apologies to the memory of Christina Rossetti, for messing up her poem "Sing-Song.")


Some things you always wanted to know about bush flies

What do they eat?

Blood, sweat and tears. (They'll take blood from wounds -- they don't bite to draw blood.) It's the protein they are after. They also feed on dung, but the females can't get enough protein from dung to develop their eggs.

This explains why bush flies are such a pest at barbecues. They want the blood and other protein-rich juices in the meat. But at barbeques they are only looking for something to eat, not for a place to lay eggs. They never lay eggs in meat or in wounds.

And they're not usually attracted to sugary things like cakes. But they'll nibble at them if there's nothing else going.

Their minimum survival needs are for moisture and carbohydrates. These they could get from plants alone. But with this diet, the females wouldn't get protein to develop their eggs. And bush flies would die out.

Can they bite?

Not really. But bush flies do have primitive teeth ('prestomal teeth'). They can't puncture your skin with these, but they can rasp a bit around the corner of your eye -- for example -- to get some secretions flowing, or rasp over a cut to encourage the blood to flow.

Do they have a sense of taste?

Do they ever! And they taste with their feet! That's why they walk all over something before they eat.

If you like experiments, you can check this out. Catch a bush fly and put it in the fridge for a few minutes. This anaesthetises it, but doesn't kill it. Then drip a spot of wax on the end of a stick and put the bush fly upside down on it. Finally, use a hot needle to seal the fly's wings to the wax.

You've now got a fly on a handle. When it wakes up, touch its feet in water. You'll see its proboscis go into the water. When it's finished drinking, you can experiment by lowering its feet into different liquids. Try sugared water, and salt water -- and use the ordinary water as a control.

The fly's proboscis lowers and retracts by reflex. It doesn't matter whether the fly is hungry or thirsty. When its feet touch the sugar water, out zips the proboscis. With salt water, it stays in.

How long do they live?

In hot weather, they live about a week. In cool weather, two to four weeks.

Without water, they only live about a day.

How fast do they beat their wings?

About 200 times a second. (About three times as fast as a hummingbird's wings.)

How do they land on the ceiling?

They somersault. They fly along very close to the ceiling, reach up with their front feet, grab hold, and flip over.

Can they learn?

No. No experimenter has ever been able to teach flies anything. (Some have tried for 15 years.)

Fish learn. Ants learn. Snails learn. Fleas learn. Cockroaches learn. Even worms learn. But not flies.

Yet a fly has a brain. You can see it for yourself: find a dead fly, one that's still fresh, and carefully cut open its head with a razor blade. Use a magnifying glass and inside you'll see a small, grey blob. That's its brain.

Sliced through, and examined in a microscope, a fly's brain is anything but simple. Here's how one researcher puts it:

"Its complexity, its beauty, defies description. Here are thousands of cells and nerve fibres whose arrangement makes any city map or circuit diagram of any engineering marvel look like the constructions of a child." *

* Vincent Dethier, "To Know a Fly."

Can they see colours?

Probably. But the only experiments I've heard about indicate two things: bush flies don't like dark colours, and they seem attracted to yellow traps.

But house flies certainly distinguish colours. Their favourite colour is red. Experiments show that red is twice as popular as orange. After that, the preference goes: black, violet, green, blue, white and yellow.

So if you paint your kitchen dark red, it may attract house flies and repel bush flies. If you paint it yellow, you might discourage house flies but bring in some bush flies. Advice: none.

How can you tell males from females?

Look at their eyes. The male's eyes are close together, almost touching. The female's eyes are much farther apart.

There are also other ways. The wings of a resting female are almost parallel to her body. In a male, the wings stand out at an angle.

The female's body is mottled grey all over. In the male, the middle segments of his abdomen are creamy-white or yellow (except a black hour-glass pattern on the mid-dorsal line).


Do bush flies have any natural enemies (except us?)

Yes. Several species of birds eat them. So do dragonflies and asilid flies.

The sphecid wasp also eats bush flies. The wasps take them to their nests and use the dead flies as provision, like dried meat. There are stories of bush flies fleeing when sphecid wasps appear. Because of this, fly-plagued settlers used to call sphecid wasps the 'policeman fly.'

There are predatory mites and beetles that eat fly eggs and larvae in dung. (Some of these have been brought into Australia for fly control -- but haven't been a great success.) A parasitic wasp has also been brought in -- from New Zealand.

Probably the biggest danger to bush flies comes from certain types of tiny worms. 'Nematodes' such as Habronema and Heterotylenchus infest flies, generation after generation, and help keep the numbers down.

The Heterotylenchus nematode is a real charmer. It spends all but one day of its life cycle inside the bush fly. In females, it makes them sterile. When the female bush fly tries to lay her 'eggs' on dung, she instead lays packets of Heterotylenchus larvae. These burrow into bush-fly larvae that are already developing in the dung and kill many of them. As the surviving larvae grow up and turn into flies, they carry the Heterotylenchus parasite as well.

Do bush flies spread diseases?

Doctors say it's possible for bush flies to spread eye diseases. Trachoma, for example, or maybe conjunctivitis. But this would only happen if you were very careless about letting flies get on your eyes. (And even then, the flies would have to have been in contact with an infected person's eyes.)

One doctor told me about seeing an inmate of a mental institution with maggots under his eyelids. But these would have been blow-fly maggots -- or maybe house-fly maggots. As I said, bush flies only lay eggs in dung -- not in meat, or in people's eyelids.

If you want to hear ghastly stories about flies and disease, wait until you get to our little section on house flies. Compared to house flies, the bush flies are as harmless and sanitary as boiled water.

How can I keep bush flies from breeding around my house?

Get rid of your cows!

But the serious answer is that you can't do anything to stop the swarms of bush flies that invade your back yard. Most of them breed in pastures out of town.

It's no good covering up your dust bin or taking away lawn clippings. As I've pointed out, bush flies don't breed in anything but dung. (But you can reduce the house-fly population by covering your dust bin and getting rid of lawn clippings.)

To discourage you further about bush flies: I've heard a colourful story (which I can't confirm) that even the U.S. Navy wasn't successful in controlling bush flies around an installation in the N.W. of Australia. The U.S. Navy tried hard. They used heaps of baygon and baytex, and presumably slaughtered millions of flies. But millions more just blew in. In the end, they gave up. It was not a naval victory.

How do fly sprays work?

Knock-down sprays like Mortein work by paralysing the fly's central nervous system. The droplets of spray get into the fly by sliding down the fly's hair follicles.

The repellents are different. They contain mixtures of ingredients that confuse a fly's chemical tracking mechanism or actually revolt the fly and send it away. A few repellents also contain insecticide.

The most common chemicals used as repellents are: ethylhexanediol (EHD), N-octyl bicycloheptene dicarboximide (OBD), di-N-propyl isocinchomeronate (DPI), and N,N-diethyl-m-toluamide (Deet). Of these, Deet may have some dangers to humans, especially to infants, if it's not used correctly (CHOICE, November 1988). And with all these concoctions, it's important to follow the instructions.

CHOICE lists three repellents that contain only natural ingredients: BUG OFF, ROYAL GUARD Bug-a-way and SANDY's Natural.

They aren't as powerful as the synthetics, but you may prefer them if you worry about the effects of chemicals.

To keep flies off you at a barbeque, you are best off to use an aerosol or a roll-on, rather than a lotion. This is true no matter what brand of repellent you buy. The lotions just don't work as well.

Where do bush flies sleep?

Bush flies sleep on vegetation. They keep off the ground. They like to roost on the tips of leaves and twigs. For example, you can often find them roosting on the tips of Spinifex grass.

If it's a warm night, a bright light will sometimes wake them up and attract them.


Dung beetles vs Bush flies

Some parts of what I've said so far might have made you gloomy. Two hundred million cow pads a day, billions of flies breeding, and warm winds blowing them straight toward your barbecue.

You wouldn't be the first to wonder, "What can we do?"

About the only answer is: support your local CSIRO entomology branch! Their dung beetle programme is working. In a decade or two, the bush-fly numbers will have dropped way down. You'll still see bush flies -- a few here, a few there. But not black clouds of them. Future generations of Australians may wonder what all the fuss was about.




Why dung beetles cut down bush-fly breeding

I pointed out earlier that native Australian dung beetles can't cope with cow pads. (The pads are too big, too wet. Anyway, most Australian dung beetles live in forests, not in pastures where the cow pads are.)

But some types of foreign dung beetles can cope with cow pads. Brilliantly. And since 1967, CSIRO has been bringing them into Australia. More than 50 types have been imported to Australia, bred into large numbers, then released. They're at work now, eating cow pads, breaking them up, and killing fly eggs and larvae.

CSIRO carried out many experiments to find out how effective the dung beetles are. The upshot was this: "At all the study sites, the dung beetle fauna, whether composed of a single native species or of native plus introduced species, was capable of reducing fly survival in the dung pad to zero provided numbers were high enough."

Up to a point, the more beetles in the pad, the fewer flies come out. Also, a few big beetles have the same effect as many small ones. For example, the graphs show it takes only seven Onitis alexis in a pad to cut the fly survival rate by 50%, but it takes about 250 of the small Onthophagus granulatus to do the same job.

It works in other countries!

If any place should have an awful fly problem, it's Southern Africa. A close relative of the bush fly is there, the weather is perfect for breeding, and there are plenty of large animals dropping dung. (Even elephants.) But bush flies are scarce.

What stops them is armies of African dung beetles. Many of the beetles are perfectly adapted to elephant dung, horse dung, rhino dung, zebra dung, cow dung -- in fact, to dung from any of the large herbivores. About 2000 species of African beetles feed on herbivore dung.

Picture this: an elephant walks by, lifts its tail, and drops a huge pile of steaming dung. By the time the dung hits the ground, nearby beetles are already on red alert. Before the elephant moves very far, the first beetles are already burrowing into the dung.

It only takes the beetles a day -- and often only a few hours -- to make the dung into balls and bury it. All that's left on the surface is a few wisps of plant fibre. Staggering numbers of beetles may have been at work: in Kruger National Park in South Africa more than 7000 beetles have been counted in a single pad of elephant dung.

Under these conditions, bush flies have no chance.

But what happens in countries where foreign beetles are deliberately brought in?

For example, Hawaii. There the trouble was horn fly. Like our own bush fly, this fly (Haematobia irritans) breeds in cow dung.

In 1906, a species of dung beetle was brought in from Mexico (the first attempt -- ever -- to colonise dung beetles to control flies). A second type of beetle was brought in from Germany in 1908. But neither of these types ever thrived or spread in Hawaii.

In 1923, three other sorts of beetles were brought in from Mexico -- and these did thrive. (So did another type, brought in later from Africa: the Onthophagus gazella -- now also at large in Australia.)

As the dung beetle population in Hawaii rose, the numbers of horn flies dropped sharply. Now they are no longer a problem.

To prove that the dung beetles were responsible, some experiments were done: one batch of fresh cow pads was protected against beetles, but exposed to horn flies. These pads produced hundreds of flies each. But in another batch of pads, beetles were allowed to get into the pads. In these pads, only a few stunted flies came out -- or none.


Life cycle of the dung beetle

Dung beetles spend as much time in dung as fish do in water. They breed in dung. They feed on it. They grow up in it. The only time they aren't actually living in it -- or 'working' in it -- is when they're flying around looking for a fresh mass of it.

You probably know about what dung beetles are most famous for: making dung into balls, then rolling the balls along. But not all types of dung beetles do this. Some just tear off chunks of dung and shove them along. Other types make balls and drop them into tunnels they dig under the dung pad.

But the ball-rolling types are certainly impressive. The ancient Egyptians were so impressed they made the beetles into gods. (They compared a dung-ball to the sun, and the scarab beetle to the mysterious force that moves it across the heaven.)

The funny part of it all -- in these days of sexual equality -- is the way the male and female work together. The male slaves away, picking seeds and other useless bits out of the raw material, and tidies the dung up into a neat ball. Then with enormous struggle, he pushes it over the ground -- while the female rides on top. Maybe she's directing the way?

All types of dung beetles bury the dung balls, and the female lays her eggs in them. One egg to each dung ball. She scoops out a bit of dung from the side, lays one egg in the centre, then seals it back up.

The dung beetle larva hatches in this 'brood ball' and immediately begins feeding on the dung. The larva has special mouth parts for this: it can bite and chew -- unlike adult beetles (which can only suck juices).

The larva grows, goes through a pupa stage, then becomes a young adult beetle. It breaks out of the dung ball and struggles up the tunnel to the surface.

These young adults then search for fresh dung pads. They can fly for many kilometres, and can detect dung at great distances by smell. When they find a pad to their liking, males and females pair off, mate, and begin the cycle again.

One of the beetles imported by CSIRO is spectacularly successful at breaking up cow pads: Onthophagus gazella. It works so fast that just 40 beetles in a 1 litre cow pad can break it up and bury it in 30 or 40 hours.

Studies show that when a pad is buried this fast, it reduces bush-fly survival by 80 to 100%. And if any bush-fly maggots survive, they turn into stunted flies that reproduce poorly -- if at all.

The beetles are thorough: they never leave fly eggs or maggots in the brood balls they make. So fly-survival in the brood balls is zero.

It's important to realise that the beetles can't get out of control and eat things they shouldn't. As I mentioned, adult beetles have mouths that can only suck juices from dung. They can't live on anything else -- even if they're starving. (The beetle larvae have mouths that can bite and tear, but they can only feed on dung. If you take them out of a dung pad, they die quickly.)

Dung beetles not only help cut the fly population. They also help fertilise the soil: they bury the dung before it loses its nitrogen to the air.


Where dung beetles have been released and what they'll do

CSIRO has been bringing dung beetles into Australia since April, 1967. The first aim was to control the buffalo fly (a dung-breeder and a menace to cattle). Down the years, more than 50 species of beetles have been brought in -- from Africa, France, Greece, Spain and Turkey. They've been bred in Australia into hundreds of thousands, then released. More than 20 of these species are now thriving.

As the dung beetles began to cut down the breeding of buffalo flies, they also cut down bush-fly breeding. At first this was only a welcome fringe benefit. Later, bush flies themselves became a target of CSIRO: beetles were brought in that were aimed at bush-fly problems in different parts of Australia.

Today it's hard to keep track of what's happening. Dung beetles can fly long distances. It would cost too much money to monitor them and note what percentage of cow pads they're destroying. Australia covers 777,000,000 hectares. Just to monitor one hectare would keep someone fairly busy. Also, you won't find many volunteers willing to poke around in cow pads and identify beetles. Field workers have to be paid.

So it's an odd kind of warfare, the beetles versus the flies. When the beetles are very successful -- you know it. You walk into some paddock, and there they are, destroying cow pads. (We talk about some of these cases in a minute.)

But if you stroll around somewhere else and don't find a certain kind of beetle, it might mean:

  • They just haven't got to that area yet.

  • They're around, but they haven't bred up into large enough numbers. Your samples just missed them.

  • They've been there, but something didn't suit them -- probably the climate. So they left, or died off.

All this is a way of saying that CSIRO doesn't have complete information on how well the dung beetle programme is working -- and you couldn't really expect them to.

But the beetles are 'under control'

One thing people ask about the dung beetle programme is, "What if the beetles get out of control and start eating other things, like crops?"

No way. To repeat: the mouth parts of dung beetles are so precisely adapted to sucking juice from dung that they can't live on anything else. If they can't find fresh dung, they die. End of story. (Their larvae can chew and tear a bit, but they can't live outside of dung. So larvae are no danger either.)

Other sceptics wonder if we might be importing diseases when we bring in dung beetles. A fair point. But CSIRO has it covered: no beetles are brought in -- only their eggs. And these are all surface-sterilised.

The procedure is elaborate. CSIRO workers overseas pick fertilised beetle eggs out of brood balls. They then surface-sterilise the eggs in 3% formaldehyde solution and send them by air to the CSIRO Entomology Division in Canberra. There the eggs are washed, and put into hand-made balls of Australian cow dung. All this can take awhile, because eggs often arrive in batches of 1500 or more. One generation of beetles is then raised in quarantine.

So far, I've only talked about worries in this section. So let's end on an up-beat. The advantages of controlling flies by using dung beetles are:

  • The beetles also break up the dung and stop pastures from being smothered by dried-out cow pads. They return nitrogen and other nutrients to the soil.

  • The beetles are aimed precisely at the target pests (buffalo fly in northern Australia, bush fly in southern Australia).

  • They don't pollute pastures with chemicals and they don't require any petrol or other energy inputs.

  • After the beetles have been released in large enough numbers and become established, nothing else needs to be done. The beetles take over and do all the work. They spread to new pastures, wherever they can find fresh cattle dung.

Beetle sightings from around Australia

One type of beetle -- Onthophagus gazella (or 'O. gazella') -- has done brilliantly. Two years after its release, it had colonised 400 kilometres of Queensland coast near Townsville. It even got to Magnetic Island -- flying over 7 kilometres of open water. Later it reached Palm Island, 29 kilometres (!) off the coast. A good flier, O. gazella.

O. gazella has now been reported over most of the North of Australia, and in large numbers. By 1973, it had colonised as far south on the east coast as Newcastle in NSW.

In the parts of the year when the beetle is active (January to April), the beetles dispose of cow pads in about 48 hours.

Another African beetle that has done well is Euoniticellus intermedius. It has spread spectacularly from Sydney across northern and central Australia, to Perth in Western Australia.

In 1981, CSIRO set beetle traps at Alice Springs in central Australia and most of the dung beetles caught were types that had been brought into Australia. (O. gazella, mainly, plus some of the E. intermedius.)

In southern Australia, Onthophagus binodis has spread in Western Australia, South Australia, Victoria, New South Wales, and Tasmania.

Western Australia is a special -- and intriguing -- case of its own, and I talk about that next.

The CSIRO beetle-strategy in Western Australia (WA)

As I mentioned in "When to expect them," Western Australia has a predictable bush-fly pattern. To remind you: bush flies are first noticeable in Perth in October, keep increasing in November, and become terrible in December. Then the numbers fall off fast. By the end of January, almost all the bush flies are gone.

But an insect pest with predictable ways is an insect asking for slaughter. Which is what's going to happen. It also means WA is a kind of testing-ground for the final battle between fly and beetle.

The problem so far has been that the beetles have been fighting at the wrong time. The six types of imported beetles that are most active in Western Australia are most active in the summer -- after the bush-fly population has peaked. (See the graph.)

O. ferox (a native dung beetle) is also most active at the wrong time -- in winter. Its activity declines fast just at the time it's needed most -- in the early spring.

You may wonder why CSIRO brought in six kinds of beetle that attack cow pads after the main fly-breeding period. The answer is that the first beetles were brought in for mainly buffalo-fly control in the north. (Bush-fly problems were secondary.) Beetles were available that could help with buffalo fly -- and to some extent, with bush flies. It was the best way to start.

As a matter of record, here are the kinds of beetles already at work in WA:

O. ferox. A native species, the only kind in WA that goes into pastures and breaks up cow pads. It's most common in southern areas.

O. binodis. From Africa. It has become abundant in parts of WA that have a high rainfall -- from Albany to Perth, for example.

O. taurus. From Europe. It has spread over wide parts of WA -- but in a patchy way. ('Taurus' because the beetles have 'horns' that look a bit like a bull's.)

Euoniticellus pallipes. From Europe. It's abundant south of Perth.

Euoniticellus intermedius. From Africa. It's abundant north of Perth.

Euoniticellus fulvus. From Europe. It's established south of Bunbury.

Onitis alexis. From Africa. It's abundant from Geraldton to Mandurah.

Onitis aygulus. From Africa. It's abundant between Cunderdin and Narrogin. It looks like the Onitis alexis, but bigger.

But it's clear what else is needed: beetles that attack cow pads earlier in the spring. Three candidates have been found from Spain (where the climate is similar to the south-west part of WA). The problem is that they seem to be hard to breed in quarantine. A new programme to attack the problem began in December 1989 -- a joint project between the WA State Government and CSIRO.

The Spanish beetles have a heavy job to do: knocking out bush-fly breeding when it is at its peak. Dr. James Ridsdill-Smith from CSIRO's Division of Entomology in Perth, said: "There is laboratory evidence that it's harder to increase bush-fly mortality with dung beetles in spring than in summer. It will be several years before we expect to release enough of the beetles from Spain -- or any other suitable species -- to have a noticeable effect on the bush-fly peak here. But in time, people in Perth should be able to have December barbecues without thousands of uninvited guests."

Some dung beetle success stories

Most scientists are cautious people. So when they refer to clear successes in the beetle programme, it means something. For example, here are some typical quotes from technical literature:

"Two species of beetle in particular, Onthophagus gazella and Euoniticellus intermedius, continue to spread over huge areas of the tropics and subtropics... it is not uncommon at the height of the season to find up to 1500 beetles in a single pad."

"After the successful establishment of dung beetles, particularly of Euoniticellus intermedius (Reiche), around a release site near Narrabri, New South Wales, local residents noticed an apparent reduction in the nuisance caused by the bush fly, Musca vetustissima Walker."

"Dung beetles introduced from Africa are already significantly altering the relationships of bush flies and cattle dung in the northern half of Australia. Over large areas cattle dung pads no longer persist on the ground, due to their rapid utilisation by a variety of beetles. In one area at least a consequential reduction of bush-fly abundance has been documented."

"The abundance of M. vetustissima did not change in December, but there was a marked reduction in January, between the two years before and three years after the establishment of introduced beetles in the Busselton area."

And so forth. Cautious reports of success. And that's how it will seem: more beetles noticed in such and such a place, or fewer flies, year after year. With this kind of thing, no one can ring a bell and declare the fly problem solved. It will happen gradually.

You may wonder: have these millions of beetles caused any problems? No, not really. I've only read about one complaint: it came from a cattle raiser who'd always used dried dung to level up pipes in his fields. He complained that he now had to carry blocks of wood instead. There was no reliable supply of cow pads any more!

Well, the rest of us can live with that.


Biological control of insects isn't new

It may seem exotic to bring in dung beetles to control bush flies. But the principle is old -- and tested.

Here are some examples from Western Australia, where the Agriculture Department has put together a list. They're insects brought into Western Australia to control other insects:

Date

Pest
Predator
Brought in from




1893
woolly aphid
ladybird
Tasmania
1895
cabbage aphid
ladybird
Sri Lanka
1902
black scale
wasp
Capetown
1902
mealybugs
ladybird
Queensland
1902
cabbage moth
wasp
NSW
1904
black scale
wasp
California
1905
red scale
wasp
China
1907
soft brown scale
wasp
Philippines
1907
cabbage aphid
wasp
Sri Lanka
1933
green veg. bug
wasp
Egypt
1958
Med. fruit fly
wasp
Hawaii
1960
San Jose scale
ladybird
California
1960
red scale
wasp
India
1962
Med. fruit fly
wasp
France
1965
earthmite
predatory mite
Morocco
1975
Two-spotted mite
mite
America
1978
green veg. bug
fly parasite
Trinidad
1979
blue-green aphid
wasp
America
1979
Northern armyworm
wasp
Pakistan

Biological control of flies in Australia had its start in 1960. Dr. G. F. Bornemissza, an entomologist with CSIRO in Canberra, published an article titled, "Could dung eating insects improve our pastures?" He suggested that dung beetles would improve pastures, and also that the beetles would cut down the fly numbers. This was the first serious (and semi-official) suggestion about bringing in dung beetles.

To help prove his case, Dr. Bornemissza carried out some experiments in Hawaii in 1966. As I mentioned earlier, dung beetles had recently been released in Hawaii -- brought in from Africa and Ceylon. As an experiment, he kept beetles away from some cow pads, but let flies get to them. Other pads he left open to both flies and beetles. The results were: pads with beetles produced 95 per cent fewer flies than pads without beetles.

Dr. Bornemissza carried out more experiments in his Canberra laboratory. The results were favourable.

All this led to the first dung beetle imports in 1967.

The point is this: the dung beetle programme is part of a long history of using insect to fight insect.


Other kinds of flies

House flies

House flies came to Australia as stowaways on the early ships. It was the same way many other insects got here: the Mediterranean fruit fly, the German cockroach, flour moth, grain weevil, green vegetable bug, Argentine ant, Indian rat flea, and others.

Join the crowd

If a house fly sees a group of flies, it joins them. It will even join a group of imitation flies. This gem of fly psychology explains why the old-fashioned sticky fly paper works so well. As soon as a few flies get trapped, others can't wait to join them.

Where they breed

They'll breed near your house, if they can. It's not for nothing they're called 'house flies'. They're attracted to houses and buildings, and try to get in. (Just the opposite of bush flies, as I explained earlier.)

House flies lay eggs mainly in rotting vegetation: for example, in your rubbish bin, decaying grains, soiled rags and paper, lawn clippings and compost heaps. In fact, in almost anything that's rotting. (This is very different from the way bush flies breed -- they breed only in dung.)

If you're bothered by house flies, it usually means they're breeding somewhere close by. Very likely within 50 metres.

And they breed fast, as Health Authorities never tire of pointing out. In warm weather, a fly egg can turn into an adult fly in just eight days. Think what this means when you reckon that female flies can lay batches of 100 to 150 eggs. Every eight days or so, the fly numbers could theoretically be multiplied by 75! (Assuming half the flies are female, they get enough to eat, none die, and nothing attacks them.)

Which leads to another one of those hypothetical calculations made to emphasise a point. This one goes like this: you start with a single pair of flies, which breed in spring. Suppose 150 of the larvae live, grow into flies, pair off, and breed. Suppose this goes on all summer, with each pair producing 150 larvae. By the end of the summer, the original pair would grow to 8.56x1020 flies (865 million, million, million). Enough flies to bury all of Australia to a depth of 11 metres (packing them in at 10 flies per cubic centimetre).

Diseases they can carry

House flies are dirtier than Dirty Harry. Their bodies are hairy and their feet are sticky. Each fly can carry several million bacteria. (One lab did a count, and estimated 6,500,000 bacteria on a fly they examined.)

Not only that. Some bacteria can live -- indeed, thrive -- in the gut of house flies. These bacteria can get passed from generation to generation.

You might think house flies were invented for germ warfare, when you look at the diseases they spread:

Amoebic dysentery, anthrax, cholera, gastroenteritis, parasitic worms, paratyphoid, poliomyelitis, salmonella, shigellosis, trachoma, tuberculosis, typhoid fever, typhus.

They pick up all this stuff when they're feeding. They're attracted to all the worst locations: open toilets, rubbish dumps, overflowing sewage, partly digested or decaying food, and rotting carcasses. After a yummy protein meal from these choice sources, they're all ready for something sweet as a dessert.

If you saw the film "The Fly," you know what happens next. The house fly finds a nice cake, or open milk bottle, or the sticky face of a sleeping baby. Then it squirts out some of the liquids it's already eaten (that nice sewage, for example). This helps dissolve the cake frosting, or makes the chocolate on the baby's face nice and moist.

Then the fly drinks up part of the newly liquefied patch. So it leaves behind germ-laden vomit and probably some fly excrement as well. This is what's in those familiar fly specks you see on some restaurant walls.

How to fight house flies

Screens are important, because house flies persist in trying to get inside houses. Sprays and certain kinds of traps are useful for flies that manage to get inside.

But if you're serious about fighting house flies, there's only one effective way: wipe out their breeding places.

  1. Spread some sheets of paper in the bottom of your rubbish bin. Drain any rubbish before you put it in, and wrap each bundle in newspaper. Make sure the top of the bin fits tightly. Get a second bin, if you need to -- rather than have the first one open at the top when it gets too full.

  2. If you bury food scraps, do it before flies can breed on the scraps. Bury scraps at least 15 cm underground.

  3. Cover your compost heap with a plastic sheet, sealed around the edges. Or cover the whole heap with a few centimetres of soil. If you prefer, you can treat the outer layer of the heap with a larvicide. (Fly larvae can't live very far inside the compost heap, because the heat kills them.)

  4. Don't spread lawn clippings as a garden mulch, unless you spread the clippings thinly (no more than 2 cm deep).

  5. Throw away pet food that hasn't been eaten.

  6. Keep your barbecue clean. Ditto for your incinerator, if you put food scraps in it.

Blow flies

In cities, blow flies are less of a problem than bush flies.

But one type of blow fly is a big problem for sheep farmers. These blow flies can weaken a sheep -- even kill it. Or rather, their larvae can. The blow fly L. cuprina lays eggs in a sheep's wool. The eggs hatch out larvae, and these dig at the sheep's skin (blow-fly 'strike'.) The little wounds begin to ooze pus. The unlucky sheep is almost eaten alive.

The farmers fight back with chemical sprays and by burying carcasses (because blow flies breed in rotting carcasses, as well as on live sheep). But recently blow flies have become resistant to chemical sprays. So the hunt is on for other ways to control them. So far there has been no success in finding other insects to attack blow-fly larvae that feed on live sheep. But there is some hope for using complex genetic control methods.

The blow fly breeds in carrion or on live sheep. There are predators that attack blow-fly larvae in carrion, but these predators aren't genetically programmed to look for larvae on live sheep. For this reason, research on biological control agents has come to nothing, nor does anyone hold out much hope for the future.

But CSIRO is investigating genetic control methods. The idea is to develop strains of flies in the laboratory that have genetic defects, then release them. When they breed, their genetic defects will pass to the general blow-fly population -- and reduce their fertility, or ability to survive. The prospects for this line of attack seem fairly bright.

Sheep blow-flies came into Australia as uninvited guests in about 1880. The guess is that they came from Africa, as stowaways.

The records of blow-fly strike begin in the late 1880s. By 1915, L. cuprina had become a serious pest to the sheep-farming industry in eastern Australia. By the late 1930s blow flies had spread to Western Australia. They hit Tasmania as a big problem first in 1957. Now the blow flies are everywhere.

The good news

Fishermen find blow-fly maggots great for bait! That's about the only good news. You leave some rotting fish heads out -- and if you are lucky, there'll be some stray blow flies around. Then in a few days, you'll have some prize maggots.

Blow flies can also be indirectly useful in some murder investigations. The police can estimate the time of death of a decomposing corpse by noting how far blow flies have gone in their development. Blow flies attack human corpses in waves, just like they attack other carrion. One kind of blow fly starts things going, then other types move in and take over. Allowing for weather, forensic entomologists can date a corpse pretty accurately this way. Ain't science great.


Stable flies

You aren't likely to experience these unless you live on a farm or near a dairy. They breed in hay that's soaked in urine and dung.

And they bite. Mostly they go after cattle, feeding on their lower legs and making them kick and stamp. The stable flies follow the cows to pasture, then return with them into the dairy at milking time. (When they often take a few bites at the person who runs the milking machine.)

Stable flies look almost the same as house flies. The main difference is their mouth parts. The house fly has a sucking mouth part, ending in a spongy disc. The stable fly has a kind of needle for piercing skin and sucking blood.


March flies

March flies tend to be bigger than house flies. Some are grey, some are brown. And as you probably know, they bite hard, suck blood -- and hurt.

Their larvae grow up in mud or in decaying organic matter. They are very seasonal, and are only around for a short time.

Their scientific name: Tabanidae.


Thanks to CSIRO

When I asked for information about bush flies and beetles, CSIRO poured it out. I'd like to give special thanks to Dr. James Ridsdill-Smith, Officer in Charge of the Entomology Division, CSIRO, Perth. On my first trip to his office, I came away with a pile of papers and files that was 20 cm thick. That energetic help continued, right through the project.

In addition to giving me technical papers and answering about 200 questions, Dr. Ridsdill-Smith and his colleague John Matthiessen suggested further topics for the book. And they kindly read a draft of the whole typescript. (But errors are my responsibility, if there are any.)

I thank them -- and others at CSIRO -- who helped me. It may not be out of place to say they also deserve broader thanks for their help to farmers, and to the rest of us, who already live in a less fly-infested land because of their work.



Update, references and links, and more by the same author

By the same author

Your dog is watching you.

The Debt Book

Tips on choosing a suburb in Perth, Australia.


Update on The Fly in Your Eye

Here are two updates to the book: Dec 2007 ( Are birds eating too many dung beetles?) and Jan 1998 (The impact of dung beetles on bush fly populations). Dr. James Ridsdill-Smith from CSIRO wrote them. He supplied most of the scientific information that I used in the original book too.

References and links

If you'd like to read more about flies, a good place to start is with "The Ecology of Pests -- some Australian case histories" (CSIRO: Australia). It has a good chapter on the bush fly, and also on the sheep blow fly.

If you just want to buy one book about insects, here's the one I recommend: Bugs in the System: Insects and their impact on human affairs, by May Berenbaum. How insects affect us, like it or not. Not just by biting us (though that's covered in piercing detail), but also their benefits.

Here's a book that celebrates beetles. It's the next best thing to 20 display cases of startling and expensive specimens. These are simply the most beautiful photos of beetles. You might be opening a chest of jewellery from another galaxy -- so uncanny and captivating. An inordinate fondness for beetles, by Arthur Evans, Charles Bellamy, and Lisa Watson. Factual, reliable and clear text. It would be a fine reference, even without the photos.

I used this book as a reference when I was researching The Fly in Your Eye: To know a fly, by Vincent Dethier. Lots of insight into what makes flies tick, and what it is that makes them so intriguing to lab scientists. Why flies resemble flying microchips (with low RAM).

And if you are one of those calculating sorts who wondered about the gigantic pile-up of flies in the exponential breeding example, here are some more details on that kind of insect horror: how bad it could get with cockroaches and compound interest formula.

Eye protection, fly repellents, special hats, nets

Oct 2013

The most annoying thing is the way bushflies go for your eyes. You can stop them with safety glasses like these:

This type will fit over eyeglasses or sunnies. You can see clearly and the air holes stop the safety glasses from fogging.

But the flies can still crawl around on your face. If you find that intolerable, you can try an insect repellent. Aerogard has one that's almost odourless. It relies on the chemical picaridin, which is probably harmless. Some flies will still land on your face, but usually decide it's a bad environment and shoot right off. But before you use any repellent, you may want to make enquiries about possible effects on your health. Here's one place to start: Wikipedia background on insect repellents.

A chemical-free approach is to wear a Frillneck hat. Like this one:

Most of the flies can't work it out. They stay outside. (For the reason why, see the "Bush-fly habits and flight performance" section above.)

If you want 100% protection, then buy a hat net. Camping shops have them and they also sell hats with built-in nets. Tip: if you add some weight to the bottom of the net at the front, it will stop the net from blowing about in a breeze and tickling your face. Most nets have an elastic cord around the bottom and you can use that as a pouch. Try putting different things in the pouch until you find something heavy enough but comfortable. Some people use a pair of socks.