How dung beetles can help you

The beneficial role played by insects in agriculture should not be underestimated, and this is certainly true of dung beetles, says Paul Donovan.

How dung beetles can help you
The female buries her dung ball in a tunnel, pushing it all the way to an enlarged chamber at the far end.
Photo: Paul Donovan

As the many species of dung beetles out there go about their daily business of breaking up dung, they help to put important nutrients back into the soil, which foster plant growth.

It is often claimed that were it not for dung beetles, the plains of Africa would literally be knee-deep in animal dung!

In agriculture, cattle are among the main producers of dung. Here, dung beetles not only help to fertilise the soil – and thus provide better grass for grazing – but save the livestock industry millions of rands every year by helping to improve animal health.

If left exposed on the ground, cattle dung provides an ideal breeding ground for dangerous flies and parasites. Up to 3 000 flies can breed in two weeks on a single cow pat.

A study conducted by the American Institute of Biological Sciences in 2006 found that by burying all this dung, these beetles saved the US livestock industry a staggering US$380 million (R3,9 billion) annually.

Rolling the ball to safety
Collecting dung is usually the female’s task. She forms a neat ball from the dung pile, then rolls it with her rear legs – over and around obstacles if need be – seeking a suitable burial spot some distance away.

Research has shown that dung beetles use the position of the sun by day and the angle of the Milky Way by night to navigate themselves rapidly away from the dung pile, where competition is fierce and beetles try their best to steal each other’s dung balls.

Different species, different habits
When she finds a burial spot, the female leaves the ball and digs into the ground to create a tunnel 30cm to 40cm in length, depending on the species.

At the end of this tunnel, she digs an enlarged chamber to deposit the dung. Once she is satisfied with the excavation, she exits the tunnel, rolls the ball all the way into the chamber and lays an egg in the dung.

At this point, a number of things could happen. The female may fill in the tunnel with soil and go in search of more dung and a new nesting site.

Alternatively, she may bring additional dung balls to the original brood den as extra food for the larva. Sometimes, four or five dung balls are hauled into the tunnel.

Not all females work alone. Depending on the species, the male may help. Where this is the case, both beetles work to secure a site and guard the ball throughout the incubation period.

Instead of digging a tunnel, some species conceal their dung ball in a shallow depression beneath or to the side of the pile of dung from which it was cut. This ensures that the developing larva has a much greater food larder upon which to feast.

Needless to say, the threat of discovery means that it is in the female’s interest to bury several dung balls and lay an egg in each.

Dung Down Under

Cattle were introduced to Australia only in the 1880s. Although the country has several hundred species of native dung beetles, these evolved alongside kangaroos and other mammals, which have a much more fibrous diet than cattle.

As a result, the beetles cannot break down the vast amounts of dung produced by livestock.

A cow can produce up to 12 cow pats a day, and although the grass surrounding each of these will turn lush green, it is unpalatable to the cow. As a result, a considerable area of grazing land is taken out of use.

These cow pats do eventually dry up, but they take months, if not years, to break down completely.

Although some are used as a source of fuel in certain communities, far more lie dormant, and end up serving as breeding grounds for undesirable insects and parasites.

The problem became so severe in Australia that a programme was initiated between 1969 and 1987 to deal with it. The Australian Dung Beetle Project, led by Dr George Bornemissze under the auspices of the Commonwealth Scientific and Industrial Research Organisation, introduced beetle species from South Africa and Europe.

A total of 23 species were successfully established.

The project monitored the effects of the beetles and found that pasture quality and fertility improved significantly and there was a 90% reduction in localised bush fires.

Paul Donovan is a biologist who has worked with reptiles and insects in zoological collections in the UK. He is based in Botswana, where he advises farmers on the use of biological control agents.