Dung beetles are members of the scarab family that harvest an abundant resource: poo. They feast on it, bury it and lay their eggs in it. Some harvest it by rolling balls of poo larger than themselves along the ground.
Of all the poo-eating creatures in the world, it’s only some species of dung beetles that are capable of rolling poo balls. Or is it?
Scientists from our Australian National Insect Collection recently filmed a spectacular poo-rolling performance by a weevil and named three new species in the process.
The world of beetles
Beetles are possibly the largest group of animals on Earth.
The scarab beetle family has more than 30,000 species. They include dung beetles, Christmas beetles, beetles with shiny-metallic colours (like Chrysina resplendens) and the beetles that inspired jewellery and amulets in ancient Egypt. Their larvae mostly live underground and are pale-coloured grubs shaped like the letter C. Many scarab species are nature’s recyclers, feeding on decaying animals, plants and poo.
Weevils are a different group of beetles. Almost all weevil species feed on plants (like the cabomba weevil). They are easy to recognise thanks to their long snout, which they use to drill into plant tissue to feed or lay eggs. There are close to 200,000 species of weevils in the world. But only about 62,000 have scientific names so far.
Some weevils in the genus Tentegia live in monsoonal and arid parts of Australia. They specialise in harvesting marsupials’ dung, in a remarkable case of convergent evolution (the independent evolution of similar features in different species) with scarab dung beetles.
Our beetle taxonomist Dr Hermes Escalona filmed the dung rolling behaviour of these weevils at Undara Volcanic National Park in north Queensland. This unusual behaviour was described in the mid-1960s but had not been documented until now.
"Weevils of the Tentegia clan roll dung pellets of marsupials into collections under logs. The females lay their eggs in the pellets and the larvae eat them as they develop," Hermes said.
"By eating the poo of plant-eating marsupials, they are still eating plant material like other weevils. It has just been processed through the gut of a marsupial first.
"The behaviour of rolling and eating dung is unique in insects outside of the dung beetle realm. It’s a consequence of adaptive evolution. These weevils have come to resemble dung beetles as part of their adaptation to arid Australian ecosystems."
Three new species of dung weevils
As part of their research, Hermes and colleagues Rolf Oberprieler and Debbie Jennings studied the taxonomy of Australian dung weevils. They gave scientific names to three new species of Tentegia weevils from the Northern Territory (NT). One of these lives on our site in Darwin. There are eight species of dung weevils in the NT, more than anywhere in Australia.
The team hopes their work will stimulate further studies on biology and distribution of these fascinating and poorly known weevils. They also hope it will aid in conservation, given that several species appear to be rare, living only in small areas.
Introduced dung beetles
Australia has more than 500 native dung beetle species, but they’ve evolved to clean up the small, dry, fibrous poo of native marsupials. Therefore, huge, wet cow pats aren’t on their menu. Because of this, cattle farming in Australia created an endless breeding ground for native bush flies and midges, which boomed in numbers and became pests.
That’s why, back in the late 1960s, we began importing dung beetle species from Africa and the Mediterranean. These carefully chosen recyclers dealt with cow pats on farms, which improved pastures and solved Australia’s fly problem.
The paper, A dung-beetle impostor: revision of the Australian dung-weevil Tentegia Pascoe (Curculionidae: Molytinae: Cryptorhynchini) with remarks on the natural history of Tentegia stupida (Fabricius), was published in the journal Annales Zoologici 2023, 73(1).
We would like to thank the Queensland Department of Environment and Science, the Ewamian people and The Undara Experience for facilitating permits and access to the site.