A “NEW CHUM”

I came to Australia as a young graduate biologist from the UK, to work on a CSIRO project to introduce exotic dung beetles to Australia.  Native Australian dung beetles prefer the small, dry droppings of kangaroos and other native animals, and they don’t like the large wet droppings of introduced cattle.  The result was that large areas of pasture were lost because the cow pads sat on it for ages, and nuisance flies bred in the cow dung.

So CSIRO brought in beetles that preferred large cow droppings, mainly from Africa, under very careful quarantine.  The first beetles were ones that were adapted to climates like north Queensland, and I was posted to a small lab in Townsville.  The lab was the old mortuary of the Townsville General Hospital, though the only way you could tell its former use was by the drain holes in the middle of the floor.

My job was to go round cattle properties in the north, to tell the graziers about the project and hopefully to get their permission to release the beetles on their land.  This was an interesting experience for a raw Pom, brought up in an English city.  I’d never been near anything bovine in my life, and I had to explain about exotic dung beetles to some quite sceptical Australian graziers.  I learned very quickly about the Australian sense of humour, being on the receiving end of quite a bit of it for a while.  Though after time I learned to give a bit of it back too.  And I learned to love cattle, too, especially the beautiful white Brahmans.

After we’d released beetles on the first few stations, I had to go back to check whether they were established and breeding.  I would go into the release paddock and bend over fresh droppings looking for signs of beetle activity.  Then I would look up and find a ring of cattle right around me, staring in amazement at this strange being peering at their droppings.

I gulped a bit at first when a Brahman bull, weighing close to a tonne, would amble up to me in the paddock.  Not to attack – it just wanted to have its nose scratched.  Really hard….  The only time I had anything like aggression was once when I got too close to a Brahman calf, and its mother came up to me.  It didn’t attack me – it just put its nose into my back and gently but very firmly pushed me away until I was a suitable distance from its calf – then left me again.

That was the beautiful Brahmans, and Herefords, Brafords and Shorthorns were similar.  But I did once go into a paddock that contained a bull that was either Jersey or Guernsey, and they are notoriously aggressive.  Fortunately I saw the bull in the distance as it began to snort and paw the ground.  I shot back out through the fence, not waiting to check which of the two breeds it was.

From my base in Townsville I travelled more and more widely into northern Australia to spread the word about the beetles, and then to release the beetles themselves.  I visited cattle stations around the Gulf Country and up the Cape York Peninsula, which gave me the background for the locations in the book.  Eventually I extended into the Northern Territory and across to Broome in Western Australia, and beetles have now been released throughout those areas.

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FLIES AND MAGGOTS

You will be thinking that none of this has anything to do with maggots, but the connection is that one of the problems with uncleared cow dung is that various different flies breed in it.  Two of these are pest species – the bushfly that comes in abundance to humans to suck sweat, and the buffalo fly which is a blood-sucking pest of cattle.  One of my jobs was to assess the impact of dung beetles in reducing the breeding of these pest flies, and we used to take standardised samples from dung pads to count the number of flies breeding in them.

We used to hold the sample until the adult flies bred from it, and then count the flies.  However, the problem was that when you remove the samples you interfere with the flies’ development, and too many died before they emerged as flies so the count was invalid.

The solution was to collect the developing maggots without waiting for them to become adult flies, but the problem then was that to the untrained eye most of the maggots look the same – small, white and squashy.  No guide to maggot identification was available, so I had to learn which was which species, and how to tell them all apart.  In the life history of a fly the female fly lays eggs, the egg hatches to a tiny first stage (or instar) larva; after a day or two that moults to become a second stage, and in a couple of days more it becomes a third stage.  The third stage exists for longer, and is the stage that does most of the feeding.

When fully fed the third stage goes quiescent, and its outer skin or cuticle becomes rounded and hard, forming the puparium.  Inside the puparium the remainder of the third stage larva turns into an adult fly, and eventually the puparium splits and the adult fly emerges.  Its wings are scrunched up because there is no room inside the puparium for them to spread.  When the adult emerges it is very soft, and it sits quietly for a while to harden its own cuticle off and blow up its wings.  Eventually it is able to fly away, and the cycle repeats itself.

It is almost impossible to identify fly eggs – they are all slender, cylindrical and white, though some species lay them all together in a batch and some spread them singly throughout the dung pad or other breeding medium.  It is almost equally impossible to identify first instar larvae because they have very few characteristics to separate them – they are all tiny and almost featureless.

The second instar larvae have some characteristics that resemble those of the third instar but simpler, but it is really the third instar that one needs for an identification.

In The Coolabah Creek Maggot Inspector Alan Campbell said that all maggots look the same – soft, white and squashy, and good for fish bait.  That was pretty much my own conclusion too when I first looked at what I was finding in the dung.  However, after a little time some differences became apparent.

The most significant features of a maggot are its hind spiracles, through which it breathes.  A maggot has two tubes inside its body, running the full length of the body.  At the front end each tube opens through an anterior spiracle, which has some use for identification, but the best characters are the hind spiracles that open through the flattened back end of the maggot.  Each spiracle is a broad plate, typically with three elongate slits through which air passes in and out.  Sometimes there are more than three slits, and sometimes there are many small round holes instead of slits.  The shapes, numbers and patterns of the slits are the best way to sort out which species of fly you have.

The other distinctive feature of a maggot is its head skeleton, though this tells you more about the diet of the maggot than it does about its identity.  The head skeleton comprises two mouth-hooks and two one or two pieces behind that.  Maggots that feed in dung have flattened mouth-hooks like small spatulas for shovelling wet dung into their mouths; blowfly maggots have sharp slicing blades to cut meat off; maggots that feed in living plant tissues have mouth-hooks with tiny saws to cut the plant tissue.

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MY WORK ON MAGGOTS

My study started at first on finding ways to distinguish the maggots of each of the fly species breeding in dung in northern Australia, and in the course of that I found that while the adult flies are very well known and described, very little existed on the detail of the maggots.  My study for CSIRO provided descriptions of the maggots of 29 different dung-breeding flies, with just a few species missing where I couldn’t obtain enough material.  This gave us a way to measure the effects of the dung beetles without having to breed out adult flies first.

When I first started that study, I shared everyone else’s view that maggots were featureless and couldn’t be told apart.  It took a while before I got my eye in and began to distinguish each one.  I then realised that most other entomologists were in the same boat, and couldn’t tell maggots apart either.  However, there are many situations in which it is vital to be able to distinguish the maggots.  Forensic science is one; quarantine is another.  For example, Australia has many different blowflies but it doesn’t have screw-worms.  That is a dangerous pest that is present as close as Indonesia, and it would be devastating to Australia’s cattle industry if it got in here.  So it is vital to be able to tell its maggots apart from the native blowflies.

Fruit flies are another large group where Australia has many species, but a number of other dangerous species exist in neighbouring countries.

Between 1948 and 1952 the German entomologist Willi Hennig published a guide to the maggots of all known fly species.  However, when I started my study nearly 30 years later, a huge amount of further information had been published since Hennig.  I first thought of preparing an updated version of Hennig, but the quantity of new material made it more sensible to prepare a totally new, comprehensive work on the subject.  With support from the Australian Biological Resources Study I compiled a two-volume, 907-page work, A Guide to the Breeding Habits and Immature Stages of Diptera Cyclorrhapha, covering over 90 different families of flies.

And in the course of that work, like Gil Reynolds in The Coolabah Creek Maggot, I came to have a great respect and affection for fly maggots.  They are quite fascinating little things!

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