The emu as a possible explanation for the nuisance of the bush fly in aboriginal Australia

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The bush fly (Musca vetustissima https://inaturalist.ala.org.au/taxa/338075-Musca-vetustissima) is remarkably abundant over much of Australia (https://www.abc.net.au/news/science/2017-01-26/salute-the-great-australian-bush-fly/8211770).

It has no apparent counterpart on other continents in terms of a widespread public nuisance (https://blog.csiro.au/wp-content/uploads/2012/08/0005_csiro1.jpg and https://www.alamy.com/flies-on-a-womans-back-in-outback-mullewa-western-australia-image7472807.html and https://www.alamy.com/brunette-woman-in-the-outback-of-australia-protected-with-a-mosquito-net-over-hat-and-head-image224398897.html and https://www.alamy.com/stock-photo-woman-wearing-an-aussie-cork-rimmed-bush-hat-to-keep-away-flies-litchfield-23547896.html).

We know that this species - despite acting like an introduced pest - is indigenous to Australia.

The first European explorers noticed the abundance of the bush fly as soon as they reached the shores of this continent. Indeed, the bush fly may be the first member of the indigenous fauna of Australia ever recorded by Europeans.

It may previously have been assumed that the bush fly bred mainly in human and canine faeces, before the introduction of livestock to Australia. This is because the species depends on faeces during its larval stage and the pellets of kangaroos and other wild mammals were unsuitably small and dry.

However, the idea that the swarming populations of the bush fly observed in Australia as early as 1629 could have been owing to an abundance of human and canine faeces is mathematically absurd.

The aboriginal population was so sparse that each England-size part of this continent contained, on average, only about as many persons as a high school does today (https://en.wikipedia.org/wiki/Indigenous_Australians).

And the dingo (Canis familiaris), which bred exclusively in the wild and was not kept captive once adult, probably competed with the bush fly in consuming human faeces, rather than providing a net supply of breeding medium for the larvae.

The abundance of the bush fly under natural conditions in Australia can consequently only be explained by a supply of suitable faeces from some other indigenous animal.

How about the emu (Dromaius novaehollandiae https://www.inaturalist.org/taxa/20504-Dromaius-novaehollandiae)?

For the rest of this Post, I have copied my writings (including figure captions) on this topic for Wildlife Australia magazine, with associated edits.

Please see https://search.informit.org/doi/abs/10.3316/informit.163353703246236?download=true

Milewski, Antoni (2016) A new perspective on our embarrassment of flies. Wildlife Australia vol. 53, no. 2, pages 21-23 (edition of Spring 2016)

A NEW PERSPECTIVE ON OUR EMBARRASSMENT OF FLIES

Little known is that among murder and mayhem the first record of a distinctively Australian organism was inadvertently made. Life was grand for bush flies after Europeans introduced cattle – one large cow pad can produce up to 3000 flies. But there is now a lot of competition, with 23 new dung beetle species introduced since 1969 to help process cattle dung. The faeces of native wildlife (top) is far less productive. Photos: Grayham Bickley (bush fly), Neil Zoglauer (dung beetle)

Little known is that among murder and mayhem the first record of a distinctively Australian organism was inadvertently made.

Life was grand for bush flies after Europeans introduced cattle – one large cow pad can produce up to 3000 flies. But there is now a lot of competition, with 23 new dung beetle species introduced since 1969 to help process cattle dung. The faeces of native wildlife (top) is far less productive.

Photos: Grayham Bickley (bush fly), Neil Zoglauer (dung beetle)

The first European ‘settlement’ of Australia could hardly have begun with more of a bang – and buzz. In June 1629 the Dutch ship Batavia was wrecked on Morning Reef, near a fly-ridden coast off Western Australia. Flies were among the least of the worries of the 282 men, women and children who escaped drowning. The ensuing psychopathic saga has passed into infamy. Little known is that among murder and mayhem the first record of a distinctively Australian organism was inadvertently made when Commander Francisco Pelsaert wrote in his diary about the nuisance presented by a fly: ‘There was … such a host of flies, which came to sit in the mouth and the eyes, that they could not be beaten off.’ He was writing of the bush fly (Musca vetustissima).

Had bush flies not been so irritating, prompting Pelsaert and subsequent European explorers to complain about them in their journals, it would be easy to assume they had been introduced from more vulgar lands overseas – like the cane toad, the misleadingly named Australian sheep blowfly (Lucilia cuprina) and the closely related house fly (Musca domestica). The first European visitors to other southern continents recorded nothing resembling the bush fly. Pelsaert himself stopped at the southern tip of Africa and found no flies. A similar species, Musca sorbens, called the eye fly for its irritating attraction to the human face, occurs in Africa and Asia. It made life hell for Australian soldiers at Tobruk. But it has never been recorded in remote bushland or on offshore islands as small as the Houtman Abrolhos off Western Australia, where survivors of the shipwrecked Batavia and murderous mutineers huddled in terror for months. The eye fly swarms only near livestock and among humans, and is not as insistent as the bush fly on riding the human body.

The bush fly puzzle

The bush fly swarms across much of Australia and probably pestered the Aboriginal population for the 50 or more millennia before Europeans arrived. Although we may joke about the ‘Aussie salute’, deep down we must be puzzled by this biological disgrace. How can it be that the bush fly, which depends on faeces for its maggots, belonged on a continent as clean as Australia was before Europeans started farming livestock here?

Cattle are now the main animals providing faeces for the bush fly, which is why the introduction of dung beetles from Europe and South Africa has been successful in reducing their numbers. But what did these flies breed in before farming?

Although the bush fly breeds well in human and dog faeces, it would be innumerate to suggest they were the main habitat for the larvae. People were mostly too sparse, with the average England-size portion having an Aboriginal population no larger than the average high school today. And dingoes, also sparse, have been in Australia only a few thousand years. They probably competed with the bush fly near human camps by scavenging human faeces.

Among Australia’s indigenous fauna there are very few candidates for the production of suitable faeces in sufficient quantity. By ‘suitable’ I mean initially wet enough to stay moist for the 3–4 days of larval development, nutrient-rich to facilitate rapid growth, and not highly attractive to dung beetles. The faecal pellets of the marsupial herbivores, particularly kangaroos and wombats, are too small, fibrous and dry.

The prime suspect must be emus. Although barely mentioned in connection with the bush fly, everything about them seems

22 | Wildlife Australia | WINTER 2016

The bush fly has a positive side – as a pollinator. Here, a bush fly takes nectar from a trigger plant (Stylidium species) in Western Australia – in
this case without activating the trigger and therefore not helping with pollination. The bush fly and other flies are particularly important in alpine areas, where other pollinators are often scarce. Photo: Jean and Fred Hort

Keep an eye out for emu faeces and bush flies. Emus are acknowledged as important agents for dispersing seeds. They probably also once provided the main habitat for bush fly larvae. Photos: Michael Schmid (emus), Tony Rodd (emu faeces)
ECOLOGICA

to make sense. Their former population is likely to have been far greater than that of humans, and they produce copious quantities of faeces. They are Australia’s largest terrestrial animal: female adults weigh on average more than females of the largest kangaroo species, and are second only to the southern cassowary in body mass.

The emu diet is varied – including shoots, fruits, flowers, and invertebrates – and richer than the mainly grass diet of cattle. Owing to a lack of a large gizzard or large intestine, their digestion is remarkably superficial. Instead of thoroughly digesting a limited amount of food, as cattle do, they are like elephants in eating and defecating rapidly. Food items are often clearly identifiable in their faeces, some still green.

Emus need to drink and are like cattle, but unlike most large herbivores and omnivores, in producing unusually moist faeces. At times their faecal pat is downright sloppy. But it tends not to set as firmly as cattle pats do, being ropier with intact items as large as banksia blooms and sheoak cones.

The bush fly would have had emu faeces all to itself, because no indigenous dung beetles seem able to deal with material of this texture – an odd combination of sloppy and ropy. Dung beetles need a consistency suitable for breaking up into sections that can either be rolled off or buried on the spot.

Pelsaert, even if he had been of a mind to ponder the biology of the bush fly, could not have suspected the existence of a bird as strange as the emu. It was first recorded by Europeans 67 years later, by the captain of another Dutch ship, Willem de Vlamingh, who was searching for survivors from a 1694 shipwreck. He attributed the footprints he saw in Western Australia to a ‘Kasuarius’. He missed the connection to bush
flies, and so has almost everyone else since.

Although occasional mention has been made of bush flies breeding in emu faeces, no scientist has studied this. Part of the reason may be that, whereas kangaroos have become more common since European settlement, the opposite has happened to the emu. It may be a case of ‘out of sight and out of mind’ given that the niche of this bird would be occupied by a large mammal almost anywhere other than in the Antipodes.

Perhaps bush flies should join the emu on Australia’s coat of arms.

It has been suggested that this unloved member of Australia’s fauna is responsible for the tendency of Australians to mumble. More credibly, the bush fly may be responsible for spreading some pathogens – the bacterium Neisseria gonorrhoeae, which can cause conjunctivitis, and Chlamydia trachomati, which causes trachoma. The bush fly is a prime suspect in the escape of rabbit hemorrhagic disease virus from an Australian quarantine facility in 1995. Photo: Andreas Lambrianides

A NEW PERSPECTIVE ON OUR EMBARRASSMENT OF FLIES
 
The first European arrival in Western Australia could hardly have gone off with more of a bang. Actually, a combination of crash and buzz.
 
The Dutch ship Batavia was wrecked north of Perth in 1629 on a fly-ridden coast. As it turned out, flies were the least of the worries of the 282 men, women and children who escaped drowning. What ensued among the survivors – a psychopathic saga stranger than fiction – has passed into infamy. But among the mayhem the first discovery of a distinctively Australian organism was inadvertently made. For the commander, Francisco Pelsaert, had the presence of mind to record in writing the nuisance presented by the bush fly (Musca vetustissima).
 
(I think a short summary of the shipwreck events should be provided somewhere, eg. in a caption, for those who don’t know it. A relevant quote from Pelsaert to include: ‘There was also such a host of flies, which came to sit in the mouth and the eyes, that they could not be beaten off.’)

Had he and various other European explorers not recorded the bush fly during aboriginal times, it would be easy to assume that this species has been – like the cane toad, house fly and misleading named Australian sheep blowfly – introduced from more vulgar lands overseas. Our insect is a pest that swarms across much of Australia. Although we may joke about the ‘Aussie salute’, deep down we must be puzzled by this biological disgrace. And yet by all the evidence the bush fly is as indigenous to Australia as the human species is. It probably pestered the aboriginal population for the full 50 millennia before European arrival.
 
But breeding in what? How can it be that the bush fly, which depends on faeces for its maggots, belonged on a continent as clean as Australia in aboriginal times?
 
The first European visitors to other southern continents recorded nothing resembling the bush fly – least of all when shipwrecked. Pelsaert himself stopped at the southern tip of Africa – at the site of Cape Town long before its founding – and found no flies there. A similar species, called the eye fly (Musca sorbens) for its irritating attraction to the human face, does occur in Africa. Indeed, it made life particularly hellish for the Australian soldiers at Tobruk. However, it has never been recorded in remote bushland or on offshore islands as small as the Houtman Abrolhos of Western Australia, where the survivors of the wreck of the Batavia were to huddle in terror for months when Francisco Pelsaert saved the day for some of them by navigating – against all odds - a 9 m boat as far as Java to fetch help. Instead, the eye fly of Africa and mainland Asia swarms only near livestock and among human desperation, and even there is not as insistent on riding the human body as is the bush fly.
 
There were, in the indigenous fauna of Australia, only a few candidates for the production of suitable faeces in sufficient quantity. None of the marsupial herbivores – particularly kangaroos and wombats - were suitable, because their faecal pellets are too small, fibrous and dry.
 
To be ideal for the bush fly, faeces should start wet enough to hold enough moisture for the whole of larval development; nutrient-rich enough to allow rapid growth of larvae; and not particularly attractive to dung beetles including the many indigenous species.

Although the bush fly breeds well in human and canine faeces, it would be innumerate to suggest that these were the main food for the larvae. Aboriginal people were so sparsely distributed that the average England-size portion of Australia had a population equivalent to the average high school today. And the dingo competed with the bush fly rather than being a net provider of faeces, for part of its attraction to human camps was no doubt the scavenging of human faeces as food.
 
The paper by Williams 2013 suggests the Aboriginal population exceeded 1 million at its peak in which case an England-sized portion of Australia would have averaged 20,000 people (larger than high school populations). Would this have been sufficient to sustain bush fly populations? Antoni replies: not by a long shot.

But yes at other times the population would have been much less. The other question is about the contribution by dingo faeces, for presumably many dingoes did not live around human camps, so would have been an additional source of faeces beyond camps. Antoni replies: as a predator, the dingo occupies a position in the food-chain where it is naturally sparse. Furthermore, canids in the wild digest their food more thoroughly than do pampered domestics, because they have relatively little food. I don't think the dingo can be taken seriously as a breeding substrate for the bush fly, and besides it is thought to have arrived relatively recently (a few thousand years) in Australia.

Readers will of course know that the main animals providing faeces for the bush fly today are domestic bovines, which is why the introduction of dung beetles from Europe and South Africa has been so successful in reducing the numbers of this pest. However, our puzzle is about the original Australia before any farming began.
 
The prime suspect in the indigenous fauna turns out to be the emu (Dromaius novaehollandiae). Although this bird has been underplayed in connection with the bush fly, everything about it seems to make sense.

You might have to say ‘largely overlooked’. We’ve found 3 mentions of them using emu dung. (1) Two European researchers - Thomas & Jespersen (1994) – say bush flies will ‘develop in the dung of cattle, sheep, horses, camels, emu, dogs, swine and humans’. They don’t provide a source for that. (2) Jim Heath says (but not in a journal paper, see http://www.viacorp.com/flybook/fulltext.html): ‘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).’ Again, no source and you say they don’t breed in kangaroo dung. (3) A 1987 article in Ecos says: Before European settlement its major breeding sites would have been the faeces of large marsupials, humans, dingoes, and emus.
The original population of the emu in aboriginal times is likely to have been far greater than that of the human species. Testimony to the density of the population of emus is their survival until the time of European arrival on islands such as Kangaroo and King Islands, where aboriginal people had died out.
 
The emu is an omnivore, with a diet emphasising shoots, fruits, flowers, and invertebrates. Its diet is richer than that of bovine livestock, which eat mainly grass.
 
In contrast to other large flightless birds such as ostriches, the emu has remarkably superficial digestion owing to its lack of a large gizzard or large intestine. Instead of digesting a limited amount of food thoroughly as bovine ruminants do, it is similar to elephants in consuming food rapidly and defaecating rapidly, with various items clearly identifiable in its faeces. Indeed, some items are still green.
 
The emu – which depends on drinking water - resembles bovine ruminants in producing unusually moist faeces in contrast to most large herbivores and omnivores. At times the faecal pat is downright sloppy. However, it tends not to set as firmly as we see in ‘cattle pats’, because emu faeces are more ropy than ruminant dung, containing intact items as large as banksia blooms the casuarina cones.
 
The bush fly would have had emu faeces all to itself, because none of the indigenous dung beetles seems able to deal with material of this texture. Dung beetles need faeces to be of a suitable consistency, that they can break up into sections that can either be rolled off or buried on the spot. Emu faeces defy this because they are an odd combination of sloppy and ropy. And a search of the literature confirms that no indigenous species of dung beetle has been recorded consuming emu faeces.
 
How confident are you that indigenous dung beetles don’t use emu dung? There is a fleeting reference in ‘Dung Beetles Downunder’ to dung beetles using emu faeces - ‘The native species that prefer grassland and do not breed in cattle or sheep dung will suffer significantly because of the absence of their preferred dung types (marsupial, dingo, emu) from the pasture environment’.. Antoni replies: James Ridsdill-Smith did a literature search on my behalf and found to reference to any indigenous dung-beetle in emu faeces (please see the email I forwarded to you).

Although a bird, the emu is actually the largest of all terrestrial animals indigenous to Australia, besides the human species. This is because the adult female on average weighs more than the fully mature female of the largest species of kangaroo, and is second only to the southern cassowary in body mass.
 
Pelsaert, even if he had been of a mind to ponder the biology of the bush fly, could not have suspected the existence of a bird as strange as the emu. As it happens the emu was to be recorded for the first time 67 years later, when another Dutch captain, Willem de Vlamingh, visited a nearby part of the Western Australian coast in search of any survivors from a subsequent shipwreck of 1694. But although de Vlamingh’s crew were the first Europeans ever to have the opportunity to put the concepts of ‘bush fly’ and ‘emu’ together, they missed the connection and so has everyone else until today.
 
Although the bush fly has been nominally recorded breeding in emu faeces, no scientist has specifically studied this. Part of the reason may be that, whereas kangaroos have become far commoner with European settlement than they were in aboriginal times, the opposite has happened to the emu. It may be a case of ‘out of sight and out of mind’ given that the niche of this bird would be occupied by a large mammal anywhere other than in the Antipodes.

Or – notwithstanding the occasional reference to emu dung – it may be that the question hasn’t been of interest to researchers because the main focus has been on mitigating their impacts? Antoni agrees.

Antoni's attempt to close the storyline:

A strange twist to the story of the Dutch shipwreck unfolded many centuries later, during the second World War and just after the last of the original resistance to European invasion in the remote centre of Australia. Hundreds of aboriginal men signed up to fight for Australia in WWII, and several of them found themselves in the trenches at Tobruk in eastern Libya. Letters to home from this battlefield told of the flies being almost as hard to bear as the deadly hazards, for there were enough emergencies on the way to the pit latrines that the eye fly managed to breed in large numbers. Just as Pelsaert's Dutch found themselves in an overseas hell ridden with flies, so the Australian diggers must have felt similarly abandoned and maddened by the conditions of this desperate battle against the odds in Libya. And for any aboriginal man who had enlisted straight from the outback and experienced Tobruk as his first intimate acquaintance of a faraway continent, it must have seemed obvious that not just Australia, but the whole world, was the domain of these strangely ambivalent insects.
 
Extra information, possibly to include in captions:

Life history & what it implies about their dung needs – eg. The eggs hatch after only a few hours (after 7 hours at 32C). Larval growth is also rapid –the development of the three instars is completed in 8 h, 10 h and 49 h, respectively, in moist cattle dung at 32°C.
The impacts of dung beetles on bush flies as competitors for dung.
Other quotes about bush flies – eg. Lieutenant John Lort Stokes from the Beagle: ‘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.’

Ernest Giles: ‘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.’

Posted on June 11, 2022 05:29 PM by milewski