Elizabeth Raine, DPhil in Zoology (2014)
When meeting new people and asked to explain what I study for my DPhil I am ashamed to say I often try to steer clear of mentioning dung beetles. It’s not generally seen as socially acceptable to immediately start talking to a complete stranger about poo – especially over dinner, but I also don’t really want people to remember me as ‘that girl who poos in plastic bags’ (we’ll come back to that one later). However I equally feel that by avoiding talking about the group of species that I study, I am doing them a disservice.
Dung beetles use dung both as a source of food and a breeding ground, which they find by flying around and smelling out where an animal has recently defecated. They roll balls of dung often several times their own size and bury them in the ground, then lay an egg inside which grows by feeding off the dung that surrounds it. It’s tough competition for dung beetles as dung is in short supply, and males can have large horns that they use to fight one another over access to dung balls or females in order to get a chance to mate. Some beetles roll away their ball of dung with their hind legs, which allows them to escape from other beetles that wish to steal their dung so they can bury it in safety. This still isn’t always enough to stave off competition, and some dung beetles have gone one step further to get to dung first and have been found to cling to monkeys fur to be right at the source when it defecates and drop to the ground with the falling dung.[1] There have even been reported cases of dung beetles entering the human intestine through the anus, potentially to get access to decaying matter before it has even been defecated.[2] Desperate times call for desperate measures.
All of this dung activity has not gone unnoticed in the past, especially in communities in ancient Egypt where large scarab (dung beetle) species would have been a common sight feeding on animal dung. Ancient Egyptians worshiped a scarab god of the sun, Khepri, and likened the sun’s movement across the sky to a dung beetle rolling a dung ball.[3] Khepri, which translates as scarab and also means ‘come into existence’, was believed to renew the sun each day after sunset. The sun setting and rising again was associated with the burial of a dung ball under the ground from which a new dung beetle would emerge, representing birth and resurrection.[4] The sacred scarab symbol was frequently used in amulets and is included on many sarcophagi where the representation of rebirth was of particular importance.
Back to modern day, and dung beetles are still performing unexpected feats. By burying dung underground, dung beetles contribute to combining essential nutrients into the soil. There are often seeds in dung, and their dispersal and burial by dung beetles can also help improve the chances of seedling growth. Through these processes dung beetles can inadvertently improve the growth of plants which provide food and shelter for many other species within a community, making dung beetles a key part of an ecosystem.
In fact, just the act of removing dung from the surface of the soil is an essential benefit that dung beetles provide. One cow can produce around 30kg of dung a day,[5] so it’s not hard to imagine how quickly huge volumes of dung can build up through large scale cattle farming. This became an issue through the intensification of cattle farming in Australia in the 1960s. As there are no naturally occurring species similar to cows, native Australian dung beetles are poorly adapted to feed on cattle dung and instead feed on the dung of marsupial species like kangaroos and wallabies. As a result cattle dung built up massively as cattle farming intensified, stopping grass growth in pastures and providing the opportunity for the spread of cattle pests. This had the potential to cause huge environmental and economic problems for the cattle industry, and after much research several deep tunnelling dung beetle species known to feed on cattle dung were introduced to Australia. This resulted in a proliferation of the introduced dung beetle species, and spectacular dung dispersal, greatly reducing the pest problem and allowing grass regrowth for cattle consumption.[6]
Dung beetles are far more important than you would expect based on their humble feeding habits, and this is exactly why there’s a lot of research being carried out to study them in more detail. Unlike other groups of animals that researchers can go and find in order to study them, dung beetles can be quite elusive. But the clue is in the name – if there’s a source of dung around you can attract dung beetles from far and wide. Researchers use dung to attract dung beetles in a pitfall trap, which uses a source of dung suspended over a cup buried in the ground to catch the unsuspecting dung beetle attracted to the smell. When you’re working in a forest there are often few sources of dung available and as a result human dung is often used as it is especially good at attracting large numbers of dung beetles. This is exactly what I did during my field work in order to explore the role of dung beetles in a community and how much they contribute towards dung removal in a forest.
So, although it might sound repulsive to collect and study them, dung beetles are really amazing creatures that reuse waste and make it available for other organisms to use. It’s difficult to imagine how the world would work without them. Maybe we should all take the ancient Egyptian approach to dung beetles!
[1] Jacobs, J., Nole, I., Palminteri, S. & Ratcliffe, B. First come, first serve: ‘sit and wait’ behavior in dung beetles at the source of primate dung. Neotrop. Entomol. 37, 641–5 (2008).
[3] Goff, B.L., 1979. Symbols of Ancient Egypt in the Late Period: The Twenty-First Dynasty (Vol. 13). Walter de Gruyter GmbH & Co KG.
[4] Yves Cambefort, Beetles as religious symbols: https://www.insects.org/ced1/beetles_rel_sym.html accessed 16 Dec. 2016
[6] History of the CSIRO Dung Beetle Project (1966-86): http://www.dungbeetle.com.au/csiro_dungbeetle_project.html accessed 16 Dec. 2016.
Photo (top): Coffin of Djeddjehutyiuefankh with Scarab detail, 25th Dynasty,770-712 BC, Ashmolean Museum, University of Oxford. (Photograph: Elizabeth Raine)
Photo (bottom): The males of some species of dung beetle have horns, like these Metallophanaeus saphirinus that I collected during my field work. (Photograph: Elizabeth Raine. Beetles now deposited in the Setor de Entomologia da Coleção Zoológica da Universidade Federal de Mato Grosso, Cuiabá, Brazil)