Cubed wombat poo puzzle completed by researchers with the help of physics, volcanic science

wombat poos

A team of scientists from around the world — including associate professor Scott Carver from the University of Tasmania — have found some fascinating faecal facts about the wombat.

Scott and his colleagues discovered that wombats’ famously square-shaped poo was created within the intestine and not at “point of exit” in 2018, which nabbed them an Ignoble Prize — a prestigious award for science that makes you laugh and then makes you think.

However, questions about the peculiar poo still remained. Why do they fragment at such regular intervals along the length and come out as perfectly consistent little poos that are about the same length?

Dr Scott Carver

Turning to volcano science and physics to uncover the answer, the researchers have not only discovered why wombats have “perfectly consistent little poos”, but also what determines the shape of mammal poo in general.

Why look at volcanoes? The cooling process of lava beds can result in specific and regular shapes. The structures were formed because the lava they were made from cooled more slowly on the surface than internally, creating forces that resulted in regular cracking.

This got Dr Carver and his team wondering: “Does the same sort of principle apply to faeces and the sorts of different lengths and shapes that you get?” Except, unlike lava beds, the cracking of mammal poo occurs before expulsion, in the large intestine.

As food travels through a digestive system, it gets broken down and digested, leaving a sloppy “slurry” of waste, Dr Carver says. During the digestion process, the slurry enters the distal colon, where the body reclaims some of the moisture from the waste. “For a while, the moisture of the faeces is so much that it doesn’t really matter … they are still the slurry … but eventually they start to get drier,” Dr Carver said. The researchers had an inkling that this drying process created cracks through “water flux” in a similar way to how “heat flux” created the even hexagons during lava cooling.

In the lab, the team recreated the drying of waste in the intestine. Corn starch was used to simulate poo and the stand-in for intestines were plastic troughs. Heat lamps were used to dry the corn starch slurry at different rates and then the researchers analysed crack formation. The greater the drying, the more closely spaced the cracks. The water flux creates a “shearing process” that influences how regularly the breaks in the faeces occur — just as heat flux shears cooling lava. 

So, a wombat’s distinctive cubic poo is a result of the drying forces of its intestine being just right for the creation of poo that’s about as long as it is high. Mystery solved.

Their results also help to explain other animal poo shapes, which you can read more about here!