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Dung beetles

Dung beetle By gailhampshire from Cradley, Malvern, U.K - Scarabaeus semipunctatus, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=50041167

How could anyone like an animal with the word "dung" in its name? How could a dung beetle be of interest to anyone except biologists?

Background

A dung beetle's main diet consists of poop. If you want the technical term for this behaviour, they are coprophagous. It sounds revolting to humans, but it is a real service, using an otherwise wasted resource, carrying out vital nutrient recycling and ridding the world of piles and piles of smelly faeces.

The name dung beetle is used for over 5,000 different species of beetle which are found all over the world with the exclusion of Antarctica. So long as there is herbivore or omnivore dung available, they can live there.  Of course, different dung beetles for different dung producers and different strategies for utilising it.

Rollers - probably what most people would visualise if you asked them to describe a dung beetle, these species gouge out a chunk of dung and roll it away to prevent other dung eaters from stealing it. They find a suitable spot to bury their ball and use it for a food storage. Sometimes they will use it as a brood chamber and inject eggs into it. The eggs hatch into larvae which literally eat themselves out of house and home as the go through their life cycle to become adults.

Tunnelers - these species dig tunnels under the pile of dung and bring bits of dung down their tunnels for consumption.

Dwellers - these species don't bother with transport, they just live in the dung in situ.

Services

In the course of their dealing with fecal matter, beetles plant many seeds. Some of these have gone through the digestive tract of herbivores first, which softens hard coverings. Those seeds wind up in dung that the beetles then bury, effectively  planting the seeds.

Australian pastoralists had to learn the value of having dung appropriate dung beetles in place the hard way. White settlers introduced the agricultural animals that they had always farmed, without considering the consequences. Native Australian dung beetles are able to clean up poop from animals like kangaroos and wombats, but would have nothing to do with dung from cattle and sheep. Soon the paddocks were littered with pats which were attracting disease carrying insects. It took until the 1960s for Australia to import exotic dung beetles that were adapted to eating ruminant dung. This has worked in the sense of dung cleanup, and there is currently an active market for dung beetles in Australia. Before the exotic beetles were introduced, dried cow pats as hard as rock fouled the countryside, and polluted creeks and dams during rain events, providing the perfect breeding ground for flies and parasites. Australia currently has about 26m head of cattle nationwide dropping about 12 pats every day. Imagine if all that was just lying around - the stench would be horrific and the flies would be blanketing everything. This all sounds great but more research needs to be done about the impact of introducing novel elements into an established system.

There is a lack of consensus on how much influence dung beetle activity has on carbon sequestration.1

Summary of services provided for us

  • Removal of dung from ground surfaces
  • Improved nutrient recycling and improved soil structure for the purposes of grazing animals
  • Reduction of disease transmitted by flies and other insects on surface dung
  • Seed dispersal
  • Services for ecosystem stability

Threats to the services?

  • Habitat destruction - land clearing/bushfires
  • Cattle/sheep drenching may make dung toxic to dung beetles.
  • Climate change is making drought more frequent and intense, and during drought there is  less dung around so this can reduce dung beetle numbers. Once dung does become available again, flies can respond immediately and complete their life cycle in just weeks. Most dung beetles, in contrast, take at least a year to complete a generation.
  • Dung beetles reproduce deep in the soil profile. This keeps them safe from predators like birds, but if the ground stays rock hard for a prolonged period, they have a really hard time digging their way out to complete their life-cycle.

What can we do to retain these services?

  • Learn more about dung beetle ecology to inform better decision making
  • Manage toxic chemical usage to not poison dung beetles
  • Reduce greenhouse gas emissions to lessen threats from climate change consequences

Dig deeper

A tordwifel (literally ‘turd’ + ‘weevil’) used to be the word for a dung beetle.

  1. Carbon Neutral: The Failure of the Dung Beetle (Coleoptera: Scarabaeidae) to Affect Dung-Generated Greenhouse Gases in the Pasture [↩]
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