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How has unleashing an army of dung beetles changed our lives?
“Well, we can have barbecues in summer,” says Professor Nigel Andrew, an entomologist from Southern Cross University.
These introduced masters of manure have utterly transformed Australian life by slashing populations of biting flies, he says. Now, new research has revealed that dung beetles are powerful mitigators of a far worse scourge.
The idea of bringing in foreign species instantly rings alarm bells in a nation plagued by toxic cane toads, mobbed by Indian mynas and ravaged by rabbits.
But, over decades, the CSIRO has purposefully brought in more than 50 species of dung beetle from Africa, Europe and Hawaii. The science agency only recently recruited three more species from Morocco.
There are plenty of disaster stories when it comes to invasive species. Here’s how the humble dung beetle flipped the script.
Biting flies by the squillions
Skip back to the 1950s, and we had a huge problem. Cows were dumping millions of tonnes of manure across the nation. And it wasn’t going anywhere.
Cowpats are slow to disintegrate, stewing for weeks in paddocks and fouling entire fields.
Worse, the festy mounds serve as breeding grounds for bitey things. One cowpat can incubate and unleash 3000 bush flies in just two weeks, as well as blood-sucking buffalo flies and at least four types of biting midges.
One cow can produce 10 cowpats in a day. Australia now has at least 30 million cows. Scientifically speaking, that’s a shit-tonne of potential flies.
“In the ’30s and ’40s, there were just so many bushflies around areas where there were livestock, cattle and sheep and horses, it was just intolerable,” Andrew says.
Australia has about 500 species of native dung beetle, but they only go for the fibrous pellets left behind by kangaroos and wombats, and don’t work well with livestock manure.
In the late 1950s, George Bornemissza, a Hungarian entomologist who joined CSIRO, was struck by the build-up of old cowpats clogging Australian farmland. In Europe, dung disappeared in days.
Bornemissza and CSIRO began importing dung beetles that could handle cow manure. At least 55 species were introduced between 1967 and 1982.
Not all of them took hold in harsh Australian climes, but those that established permanently had a profound impact. In areas brimming with dung beetles, cowpats can be entirely “shredded” within 24 hours, restoring pasture, aerating soil and recycling nutrients.
Without them, according to one CSIRO estimate, a million hectares of pasture would be ruined each year. One study estimated their presence boosts pasture growth by 27 per cent, and the overall value of their services has been put at between $45 and $2000 per hectare.
Plus, fly populations have plummeted.
“That is what dung beetles have brought to Australia – that we are able to enjoy outside living,” Andrew said.
‘Get them while they’re sloppy’
In a new study, Andrew and his co-authors investigated how the beetles could also be cutting carbon emissions.
Lead author Dr Jean Holley and some valiant volunteers patrolled a cattle property in Bingara, northern NSW, ears perked for the plop of newly laid pats.
Dung beetles like the fresh stuff, so it was fast work to collect the dung and get it back to the lab, Andrew says: “You have to get in early and get them while they’re sloppy.”
The researchers sorted dung into cylinders and tracked the emissions emanating from the manure samples for 90 days. Some samples were populated with an array of dung beetles; others were left beetleless.
They found dung beetles slashed emissions of methane – a greenhouse gas 30 times more potent than carbon dioxide at trapping heat in the atmosphere – by 85 per cent. Overall, beetles cut emissions by 18 per cent.
Andrew and his co-authors speculate the beetles’ flurry of tunnelling, rolling, devouring and egg-laying aerates the manure, disrupting methane-producing microbes which operate in anaerobic (low or no oxygen) conditions.
Holley, from the University of New England, says their methane-slashing power adds to an already valuable repertoire.
“Not only do they recycle nutrients, reduce fly numbers and aerate the soil, but they may also help to mitigate greenhouse gas emissions from livestock production.”
Ecosystem engineer or invasive species?
Associate Professor Theo Evans, an insect expert at the University of Western Australia who wasn’t involved in the new research, says the study is well-designed and consistent with previous evidence.
Many native species of dung beetle are so small they “drown” in sloppy pats of cattle manure, he says, which is why introduced species are needed. (Perhaps a pleasant death for a dung beetle.)
But why haven’t the foreign beetles become feral pests?
Cane toads, Evans says, are “the worldwide classic example of biocontrol gone wrong” partly because they are “gape-limited predators”. That means they will eat anything that fits into the gape of their mouth.
Dung beetles, by contrast, are highly specialised picky eaters. One “wacky” native species clings beside the anus of kangaroos, he says, ready to pounce when the roo poos.
Meanwhile, the foreign dung beetle species don’t have the right mouth parts or gut bugs to eat scat from Australian native animals.
The risk of ecological disaster is much lower when you’re dealing with specialist species, Evans says, rather than generalists such as the toads.
Introduced dung beetles have been found in native bushland, but they don’t seem to be breeding there away from their precious cow manure. “There’s no evidence to suggest that the introduced species have displaced any native species,” Evans says.
Different species are also active across different seasons. Many species struggle in winter or in “shoulder seasons” such as late summer.
That’s why CSIRO has introduced another three species over the past six years to help fill these seasonal gaps: two tunnelling species (Onthophagus vacca and Onthophagus andalusicus) and a classic “roller” from Morocco (Gymnopleurus sturmi).
Andrew is interested in how a better species mix could be spread across Australia’s farmland, so dung beetles can shred manure and reduce pollution year-round.
While many people hate insects, he says, dung beetles have a charisma that sparks joy from farmers to kids.
“That’s one of the things that I really find exciting about dung beetles,” he says. “They bring together lots of different components of our community into one big, sloppy mess.”
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