We have eastern grey kangaroos and swamp wallabies coming to our grass-with-weeds (aka lawn). We don’t always see them but they leave little droppings as evidence. One day we saw one of the droppings move, then move again. Something was tampering with the evidence. In all ordered societies, some members live in luxury while others do the dirty work. So it is with insects.
We had a closer look and found that a couple of shiny little beetles were responsible and they tackled the job with relish. They were dung beetles at work. Dung beetles are members of the scarab family. They break up the droppings of other animals and bury them in the soil, both as stored up food capsules and as a place for the females to lay their eggs. This also serves the useful purpose of freeing up nutrients in the manure for use by plants. Some species make little round balls of dung and roll them to their underground chambers, while others simply bury it. Only the males do the hard yakka of transporting the balls of dung.
The beetles we saw are Australian native dung beetles, probably Onthophagus australis or O. dandalu (we can’t tell the difference), growing to about 6-12 mm long, usually a glossy metallic black/green colour. Along with other native species, mostly of the genus Onthophagus (meaning dung-eater), they have evolved to process the comparatively dry, fibrous and meagre droppings of our native marsupials.
Charles Darwin already noted this on his visit to Van Diemen’s Land in 1836. Although there are well over 350 native Dung Beetle species, some more effective than others, they had no hope of processing the high loads of manure once cattle, sheep and horses were introduced to Australia.
12 cowpats each per day
Consider this Australia has just under 29 million head of cattle, dropping on average 12 cowpats each per day.
The CSIRO addressed the situation in the 1970s and 80s by introducing 20 or so species of dung beetles from Europe, Africa and elsewhere. These aliens have evolved with herds of large animals, including elephants and buffalo and are able to deal with their droppings. One pile of elephant dung was found to contain 48,000 dung beetles which demolished it in about 2 hours. Many of these, particularly in the genus onitis, are 4 or 5 times the size of our natives and chew through piles of dung in short order. The beetles are well equipped for the task as their strong heads and mouth-parts serve as shovel, chopper, digger and rake. I guess you could refer to them as a mini earth-working machine.
European dung beetles have been observed climbing up on top of dung and making jerky movements in a sort of little dance. It was thought that this is how they orient themselves by the sun to find their nest burrows. Some recent research in Sweden has found that they actually navigate by the Milky Way. There is no data on the orientation method of our native species.
Especially interesting are the long-legged ball rollers, genus sisyphus, who make little round balls of dung and use their long hind legs to roll them to their burrows. Sisyphus was a king in ancient Greek legend condemned by the gods to roll a heavy stone up a steep hill but every time he got to the top the stone would roll down again. It was an awful job lasting for eternity but still better than rolling dung.
This ball-rolling was also observed by the ancient Egyptians who saw it as a representation of the god Ra, rolling the sun around the sky and consequently the scarab beetle became a token of veneration. When dung beetles process manure and make it available to plants as fertiliser at the root zone, they carry out other environmentally beneficial functions. Much of the carbon dioxide, nitrogen and methane by-products of manure decomposition are sequestered in the soil rather than released into the atmosphere. Dung beetles also help reduce phosphorus entering into catchments which assists in reducing the growth of blue-green algae.
Next to the tractor, these insects are probably the most useful tool for our agricultural industry. They have been a highly successful introduction. In fact, at the present time the CSIRO has two more species of dung beetle in quarantine for study before release into the field and both originate from France. Are they connoisseurs intended to handle the cordon bleu dung from our prime Angus beef?
Article — Kon Hepers