Mention dung beetles and most people will conjure up the image of industrious beetles rolling massive balls of dung away from a steaming pile of elephant excrement to the dulcet tones of Sir David Attenborough. Some people may be aware that Australia has a long and successful history of introducing non-native dung beetles to combat the mountains of dung produced by agricultural animals, particularly cattle. These beetles were introduced because most of Australia’s native dung beetles don’t cope well with the large moist pads produced by cattle.
Over 40 foreign dung beetle species have been released across mainland Australia, 23 of which have established permanently. Unfortunately, information about Australia’s suit of fascinating and unique dung beetles is overshadowed by the emphasis placed on these imported beetles due to their role in agriculture. There are estimated to be over 500 native species of dung beetle, almost 20% of which are found in South East Queensland.
Dung beetles belong to the family Scarabaeidae (the scarab beetles) and are found on all continents except Antarctica. Most dung beetles are winged, but there are a few wingless species, mainly found in rainforests. All have a keen sense of smell and characteristically branched, flat-tipped antennae.
Aptly named, the life of dung beetles revolves around animal dung. Interestingly, the beetles don’t eat the dung itself as their mandibles aren’t adapted for eating solid material. Instead, they greedily suck up the dungs’ bacteria-rich moisture for sustenance.
Dung beetles are separated into three main groups based on their lifestyle: tunnellers (paracoprids), rollers (teleocoprids) and dwellers (endocoprids). Australia’s native dung beetles only belong to the tunneller and roller groups.
Tunnellers disperse dung by digging tunnels directly underneath the dung pile. After digging their tunnels using specially adapted forelegs, the beetles break off pieces of dung and drag them into their tunnels. They then compact the dung into a brood mass into which the female lays a single egg. The brood mass is then sealed in the tunnel with a plug of soil before a new brood mass is created, which is again sealed with soil, and so the process is repeated until the tunnel is filled. As well as digging straight down, some tunnellers also dig branching side tunnels which get filled with alternating layers of brood mass and soil. Different species dig burrows of different depths, affected by soil type and moisture.
Rollers, as their name suggests, create dung balls which they roll away from the site of dung deposition using their characteristically long, usually curved, back legs. These balls are created by working and moulding broken-off dung segments, and can weigh many times the beetle’s weight. After depositing a ball into a pre-dug hole, the female dung beetle excavates a small hole into the ball, inside which she lays a single egg. She then seals the egg inside and scrapes soil over the top of her creation, known as a brood ball.
After an egg hatches, the larva spends the next period of its life systematically chomping away on the dung that surrounds it. In this way the brood mass is hollowed from the centre out, filled by the rapidly growing larva. The larva then pupates inside the brood mass and emerges as a young beetle. Depending on the species and environmental conditions this whole process can take up to a year.
Competition for a limited resource is a very common evolutionary driver between species (interspecific competition) and amongst members of the same species (intraspecific competition). Competition amongst dung beetles is believed to have driven the ‘lifestyle’ evolution of dung beetles into the different functional groups we see today.
In tunneller species this same competition has resulted in physiological evolution. Many sport spectacular horns along their bodies, which are used to defend their burrows and dung stockpiles from other beetles.
To further reduce competition, Australia’s suite of dung beetles show highly diverse traits. Different species are active at different times of the day and year, are adapted to rainforest or open forest, prefer different soil types, range in size from 3.5cm down to the size of a pin head, and show a preference for different dung mediums. There are also dung beetle cuckoos, which lay their eggs in other beetles hard won and crafted dung.
In Australia we have dry dung, which is often deposited into a hot, dry environment. Some of our dung beetles, such as Onthophagus parvus (found in SEQ), have a unique adaptation to ensure they have ready access to fresh moist macropod pellets. These beetles literally hang around the anus of macropods with their claws, which are specially adapted to cling onto animal fur. They then drop off as their unsuspecting ride deposits a fresh load of pellets.
Another fascinating dung beetle found in SEQ rainforests is the wingless Cephalodesmius quadridens. Instead of using dung or fungi these dung beetles make their own pseudo ‘dung’. The male beetle collects pieces of vegetation and fruit which he transports to a pre-dug nesting chamber. Here the female essentially creates a compost mound by chewing up the provided vegetative material and mixing it with her own faeces. This concoction composts for about a month after which the female breaks
pieces off the mound and forms them into small balls. She then lays a single egg into each of these brood balls. Due to the small size of the initial ball, the female continues to add more layers of decomposing material to the brood mass to feed the ever-growing larvae inside. The larvae signals the mother to add more material by scraping its tail across its throat. The last act of these devoted parents is to spread a protective coating of faeces, excreted by the larvae itself, across the surface of the brood ball. This allows the larva to safely finish the process of pupation before it breaks out of the ball and makes its way to the surface as a fully formed beetle, ready to start the whole process over again.
There are doubtless more fascinating stories to be discovered about the lifestyles of our Australian dung beetles. In all their various forms they are amazingly efficient at what they do and are just one more of the unsung heroes that go quietly, and often unnoticed, about the business of nutrient recycling and improving soil health.
References and Further reading
Edwards, P (2001-2002) The Queensland Dung Beetle Project.
Montieth, G. Australian Native Dung Beetles, Entomological Society of Queensland, Queensland Museum
Monteith, G & Kenyon, T (2011) A Survey of Dung Beetles from the Moggill Creek Catchment, Brisbane, A Consultancy Report to the Moggill Creek Catchment Group.
Ridsdill-Smith, J & Simmons LW (2009) Encyclopedia of Insects 2nd Edn.
Article by Tony Mlynarik
Land for Wildlife Officer
Brisbane City Council