Can dung beetles rein in cattle’s methane emissions?

When European settlers brought cattle
and sheep to Australia, they didn’t
just bring food sources – they brought
veritable poop factories. The solution to
the problem came in the form of foreign
dung beetles. The University of New
England’s Min Raj Pokhrel aims to find
out how the little critters are faring – what
temperatures they prefer and how they
might mitigate greenhouse gas emissions
– in the New South Wales Northern
Tablelands.

A single cow poops about 10 times
a day; with about 30 million cattle in
Australia, that’s 300 million cow pats
plopping daily onto the ground. In Europe,
cow dung is polished off by dung beetles.
Adult beetles bury it, eat it and lay eggs in
it, so their larvae can also feed on it once
hatched. Digging dung into the ground
also has the benefits of dispersing grass
seeds, not to mention fertilising and
aerating the soil, letting water more easily
soak into the earth and giving plant roots
room to grow.

Even though the nation boasts more
than 400 species of dung beetle, none
were up to the task of dealing with
cow poo. Native dung beetles evolved
with marsupials such as wallabies and
kangaroos. Adapted to hard, small, fibrous
poops, they couldn’t deal the big wet splats
from cows.

DUNG PATS WITHOUT BEETLES
PRODUCED METHANE EMISSIONS FIVE
TIMES HIGHER THAN THOSE WITH.

Without introduced dung beetles,
splattered dung would foul paddocks,
shrinking grazing land and providing
perfect breeding spots for disease-spreading
flies and parasites. Pats, once
they harden on the ground, can sit there
for months – even years.

Hungarian entomologist George
Bornemissza noticed this in the 1950s
when he first set foot in Western Australia.
Less than 200 years after cattle had been
introduced to Australia, cow poop was
a problem of epic proportions. Bush fly
populations were becoming unbearable,
and farmers were forced to contend with
rising worm and bacterial infections in
cattle stock.

In Europe, poop just wasn’t such a big
deal. Bornemissza wondered if Australia
could enlist some outside help. Would
introduced dung beetles clean up after
cattle?

He had to tread carefully. Introduced
species have a habit of running out of
control in Australia. After a decade of
researching dung beetles from around the world, the first large-scale release took
place in 1967. Four species – a total of
275,000 beetles – were let loose, mostly
in northern Australia between Broome
in Western Australia and Townsville in
Queensland.

Since that first cluster almost 60
different dung beetle species have been
introduced from Africa, Europe and Asia,
the most recent being Onthophagus vacca, in 2014, and Bubas bubalus, in 2015.

So how are the introduced beetles
faring – and what about their native
counterparts? These are questions Pokhrel
aims to answer during his PhD research.

He is taking stock of their populations,
counting them in 10 locations across
elevations from 300 metres to 1,300
metres above sea level in the Northern
Tablelands. Even at the highest altitudes,
Pokhrel exclaims, “We still found them!”

He is also monitoring when are they
most active – do they prefer the summer
heat or the chill of winter? – and how far
introduced beetles, which are quite good
flyers, have spread.

He’s also getting his hands dirty. Part
of his project is determining what type of
poop native dung beetles like. Has their
appetite changed with the availability of
sheep and cow dung? So far, he’s found
some native dung beetles have developed a
taste for sheep poop. This may be because
sheep dung is more nutritious compared
to that from kangaroos, he says, or perhaps
the native dung beetles have adapted to wetter, less fibrous poops. There’s
still more work to do before drawing a
conclusion.

Pokhrel is also keen to uncover what
it is about different species’ poop that
attracts dung beetles. He thought water
content might play a role, so to test this he
mixed sheep and kangaroo droppings with
water to make them the same consistency
as cow pats.

“They looked the same for me, but
it was very different for dung beetles,”
Pokhrel says. Dung beetles that preferred
sheep droppings continued to favour
them, even in their sludgy state. Likewise,
cattle-specific beetles stuck to their usual, even with watery sheep and kangaroo poop
on the menu. So how do greenhouse gases
fit into the equation? Cows burp and fart
methane – a greenhouse gas 28 times more
potent than carbon dioxide – but their
dung can pump it out too.

Grasslands and pastures are usually
carbon sinks, with plants taking up carbon
dioxide for photosynthesis. But cover
even a fraction of a paddock with cow pats and it becomes an emitter. On top of this,
methane-producing microbes prefer an
oxygen-free environment – precisely what
a sloppy, dense cow pat provides. If the
pat is broken apart and aerated, perhaps
by a dung beetle looking for a place to lay
its eggs, then carbon dioxide-producing
bacteria take over.

European and US studies have shown
this to be the case. Six-day-old dung pats
without dung beetles produced methane
emissions five times higher than those with
the beetles. Pokhrel will see if this applies
in the Australian context – and might find
yet another reason to celebrate nature’s
recyclers.