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Thursday, May 3, 2001
How dung beetles came to save Australia
By MARK BRAZIL
Second of two parts
For millions of years a whole host of landlubbers (mammals, reptiles, birds and insects) have been scouring the Earth for food and leaving behind the scraps of their meals and deposits of dung. Billions of creatures over thousands of millions of years, all dumping on the planet. Thank goodness for the natural processes of decay and for the swarms of recyclers that share our space.
The processing of animal waste that dung beetles undertake helps to greatly speed up the process of breaking down raw manure left lying on the ground. The result is a processed biowaste usable by a whole range of creatures and ultimately fueling further plant growth. The value of the dung beetle as a natural recycler is so great that certain species have even been deliberately introduced to some countries.
One is Australia. Most of the native mammals there were forest and bush dwelling. That, not surprisingly, is exactly the habitat favored by the native dung beetles. When Europeans introduced domestic cattle the dung they produced was too big, too wet and too out in the open for most native Australian dung beetles to cope with.
The millions of cowpats produced daily and left lying around provided, however, a perfect nursery for the bush and buffalo flies introduced inadvertently in the 1890s. The flies had a field day, with up 3,000 of them being reared per pat. Billions of flies swarmed across the open landscape in horrible plagues, making outdoor life a misery. Thanks to a practical research program involving the introduction of various species of dung beetles, however, future generations of Australians may even wonder why their ancestors made such a fuss about the flies.
Since 1967, more than 50 types of foreign dung beetles have been experimentally imported to, bred and released in Australia. These insect immigrants have been hard at work consuming cowpats, breaking them down and burying them -- taking them out of reach of the flies and killing the fly eggs and the larvae. With fewer nurseries available for the flies to lay their eggs in, there was a dramatic drop in fly numbers -- more than 80 percent.
The problem had not arisen in other parts of the world, such as Africa. There, large numbers of domesticated animals were also introduced, but there were already in Africa about 2,000 species of beetles perfectly adapted to feeding on herbivore dung -- elephant, rhino, zebra and so on. The horses and cattle that were introduced produced dung very similar to that of the wild grazing animals; the beetles just found more food and thrived on it.
Biological controls, such as those being attempted in Australia using beetles, have led to many notorious ecological disasters around the world. Introduced predators have so often turned their attentions to more vulnerable native species rather than prey on the rats, rabbits or snakes that humans wanted them to feed on. With the dung beetles, however, there seems little chance of their introduction going wrong. They can't get out of control.
Why not? Well, the adult beetles have mouth parts that are specially adapted to suck the juices from animal dung; they are unable to eat anything else. When there isn't enough dung to go around the beetles starve, so the supply of dung regulates their numbers. Dung beetle larvae are also specially adapted to dung: They can bite and tear at it, but they too cannot feed on anything else. Dung beetles removed from dung die quickly.
The life cycle of the dung beetle is wonderfully focused on dung. They hatch in it, grow up in it, feed on it and when they are not actually living in it, they are whirring through the air sniffing about for a fresh pile of it. Once they have located a new source to their liking, the males and females pair off and mate, and the process begins again with brood balls being rolled off for burial.
The male is a fastidious dung plasterer, picking out useless material, such as inedible seeds, from the good stuff before tidying it into a neat ball. In some species, the male excavates tunnels right beneath the dung heap. Other species invest enormous effort in producing a spherical mass that is then pushed away to a suitable spot.
The female often hitches a ride to the site, adding to the male's burden. Perhaps this is her way of checking him out. If he is still able to roll the ball to a suitable site, despite being encumbered by her too, well then, his genes are worth having in her offspring.
The beetles' fastidious behavior is part of the success story. So thorough are they in cleaning out the useless material from the dung that they leave neither fly eggs nor maggots in their brood balls. Whereas in the past Australia's beetle-free pats were perfect nurseries for flies, the introduced beetles have proliferated, spread and now make brood balls in which fly survival is zero.
The difference in Australia, where cow pats used to last for up to four years, clogging and poisoning the surface of the soil, is remarkable. With dung beetles about they are recycled within as little as 48 hours. So much dung is processed so quickly that bush-fly reproduction has been reduced by 80-100 percent.
That is not the only benefit though. The beetles not only reduce the millions of cowpats that would have otherwise have been breeding swarms of flies, they also break down the pats quickly, spreading the benefits of the dung evenly as fertilizer through the soil.
By burrowing into the soil, they aerate it and improve drainage so that the soil doesn't become waterlogged so easily, and because they bury the balls of dung quickly, they add nitrogen to the soil that would have otherwise escaped into the atmosphere in gaseous form.
So before you scorn the lowly insects, and before anyone even considers a plan to wipe them out, just think of the advantages they bring us and think of the horrible consequences of not sharing earth with them.
We would very quickly be in deep do-do.
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