If you have ever walked a bush track in Tasmania, Victoria or southern New South Wales, you may have spotted something odd sitting on top of a rock or a log: a neat little pile of droppings that look almost like dice. They belong to wombats, and they really are cube-shaped, with flat sides and surprisingly sharp corners. For years, nobody could explain how a round, soft animal produced such square droppings. So why do wombats poo cubes? The answer was finally worked out by Australian scientists, almost by accident, and the research ended up winning a prize.
A mystery solved by accident
The cubes come from the bare-nosed wombat, also called the common wombat, which lives in south-eastern Australia and Tasmania. People had long assumed the shape must be made at the very end of the digestive system, perhaps by a square-shaped opening. That turned out to be wrong.
The breakthrough came from University of Tasmania wildlife ecologist Dr Scott Carver, who was not studying poo at all. He was researching sarcoptic mange, a painful skin disease that kills many wombats, and while dissecting a wombat that had died, he found the droppings already shaped into cubes well inside its intestine, as the University of Tasmania explains. “We discovered cubes inside the soft intestines,” he told Australian Geographic. It raised an obvious question: how do you make cubes inside a soft tube?
Carver teamed up with engineers at the Georgia Institute of Technology in the United States, including mechanical engineering researcher Dr Patricia Yang. Scans confirmed that the wombat’s anus is round, not square, according to the Georgia Tech research team. The cubes were being shaped further up.
How a round tube makes square poo
The answer lies in the intestine itself. A wombat’s intestine is remarkably long, about 10 metres, or roughly 10 times the length of its body, and food takes much longer to pass through than it does in people, according to the University of Tasmania. By measuring wombat intestines in the lab and building mathematical models, the team found that the wall of the intestine is not the same all the way round. In the final section, it has two stiff regions and two more flexible regions.
As the gut squeezes waste along, the stiffer and more flexible parts of the wall stretch and contract differently, so they press on the droppings unevenly, flattening the sides and forming corners. At the same time, the wombat is drawing water out of its waste very efficiently; its droppings end up about a third drier than human faeces, as The Veterinarian reports. That drying firms the cubes up so they hold their shape. The cubes are formed in the last 17% of the colon, roughly the final metre, Carver said, so by the time they leave the wombat, they are already finished.
To test the idea, the Georgia Tech team even sewed model intestines out of cloth, adding extra stitching to create stiffer strips, and found that pulling on them to mimic the gut’s muscle contractions turned round contents into square ones. Carver has also pointed out that kangaroo droppings sometimes have one or two flat-ish sides, but nothing like the wombat’s neat corners. (The American half of the team, naturally, called it poop.)
Why would a wombat want square poo?
The shape is not just a curiosity; it may be useful. Bare-nosed wombats use their droppings to communicate. They leave them on prominent spots in their home range, such as rocks, logs and small rises, as a kind of signpost to other wombats, Carver told Australian Geographic. Many people have suggested that cubes are less likely than round droppings to roll off those perches. That makes sense, but it is worth being clear that it is a likely explanation rather than something the research has proven. What the scientists showed is how the cubes are made, not exactly why wombats evolved to make them.
A prize for research that makes you laugh, then think
In 2019, the team won an Ig Nobel Prize, the tongue-in-cheek awards presented at Harvard University each year for research that first makes people laugh and then makes them think, as the Royal Society of Chemistry notes. Their full findings were published in 2021 in the journal Soft Matter.
It is easy to giggle, but the work has serious uses. Nobody had seen cubes made inside a soft tube before, and Carver has said the discovery could inform manufacturing, clinical pathology and digestive health. The Royal Society of Chemistry notes it could even help develop new ways of detecting colon cancer, because it shows how changes in the stiffness of the intestine affect the shape of what passes through. Yang has suggested it could change how we shape soft materials, or how soft robots are controlled, and joked that she was not sure people would want cubic sausages. And for wildlife researchers, wombat droppings are a useful way of monitoring the animals’ health and numbers without disturbing them.
How you can help wombats
Carver’s original research was into sarcoptic mange, and it remains one of the biggest threats to bare-nosed wombats, along with being hit by cars. Mange is caused by a tiny mite that burrows into the skin, leading to hair loss, thick crusty skin and infections that can kill the animal. It is surprisingly common: of all the wombats reported through the WomSAT citizen science project between 2015 and 2019, 31.2% had mange, according to Western Sydney University, with cases more common closer to urban areas.
You can help in a few simple ways:
- Report what you see. The WomSAT website and app let anyone log sightings of wombats, burrows, roadkill and wombats with mange, even from outside phone range, uploading once you are back in signal. More than 23,000 sightings have been reported so far, and the data help researchers find roadkill hotspots and mange outbreaks.
- Slow down at dusk and dawn. Wombats are most active from late afternoon through the night, so take extra care when driving through wombat country around those times.
- Do not try to treat a sick wombat yourself. A wombat out in daylight with patchy fur or crusty skin may have mange; note the location and contact your local wildlife rescue group, who can arrange treatment.
Queensland also has its own wombat story: the northern hairy-nosed wombat, one of the rarest mammals in the world, survives only in a couple of protected sites in the state. It is not the species behind the famous cubes, but it is a good reminder of how much these animals rely on people giving them space.
Square pegs and round holes
So wombats poo cubes because the last stretch of their very long intestine has a wall that is stiffer in some places and stretchier in others, which squeezes their slowly drying droppings into flat-sided blocks before they ever leave the body. They probably use those blocks as signposts, and the scientists who worked it out did so while trying to help wombats with a deadly disease. Not bad for a discovery that began with a dissection and ended with an Ig Nobel Prize. If you enjoy strange Australian animal stories, see how cane toads ended up in Australia, and for another animal that is not quite what its name suggests, are killer whales dolphins?
Sources
- University of Tasmania: Scientists get to the bottom of wombat cubed poo mystery (2021)
- Royal Society of Chemistry: Wombat research that’s not to be sniffed at (2021)
- Australian Geographic: Why do wombats have cube-shaped poo?
- Georgia Tech: Ig Nobel for cubed poops
- The Veterinarian: Solving the poo puzzle
- Western Sydney University: Spatial and temporal patterns of sarcoptic mange in wombats
- The Conversation: Two biggest threats to wombats revealed by citizen scientists