The puzzle is not simply that the droppings have edges; it is how their contents acquire a regular form while moving through a living intestine. The explanation lies in the interaction between the faeces and parts of the intestinal wall with different mechanical properties.
Researchers investigated that interaction by examining wombat tissue and testing a mathematical model. Their findings help explain how the shape forms, while leaving open why wombats evolved to produce it.
The Fact, Precisely: Wombat Faeces Form Cubes Inside the Gut
The bare-nosed wombat’s relatively uniform, cube-shaped faeces are described as unique in the animal kingdom. The cubes do not take shape at the point they leave the body: their form develops inside the intestine.
A 2021 study found that the cube shape forms within the last 17 per cent of the intestine. Separated faecal cubes have been reported at about 2 centimetres long, giving a sense of their small, regular form.
The key feature is not just that the pieces have edges. Their relatively uniform shape includes corners, which the wombat’s intestinal wall helps form as the gut contracts.
How the Wombat’s Intestine Shapes the Faeces
The wombat’s intestinal wall has alternating regions of different stiffness, and these differences help create corners as the intestine contracts. Some regions were about twice as thick and four times as stiff as neighbouring regions.
As the intestine squeezes its contents, the more flexible and stiffer areas deform differently. The 2021 study proposed that this alternating pattern helps form corners as the intestine contracts.
Drying also plays a part. The University of Tasmania reports that drying in the distal colon—the final part of the colon—works with muscle contractions to produce the faeces’ regular size and corners. The shape therefore develops through both the changing properties of the gut wall and the faeces’ condition as they move along it.
How Researchers Worked Out the Mechanism
To investigate cube formation, researchers combined wombat dissections, tissue tests and mathematical modelling. This let them examine the intestine itself and test whether differences in its structure could help explain the shape.
They used histology, the study of tissue structure under a microscope, and tensile testing, which measures how tissue responds when pulled. These tests helped them compare the intestinal regions’ structure and stiffness.
The team also modelled contractions in a damped elastic ring with alternating stiff and flexible regions. In the model, contractions acted on areas with different stiffness, offering a way to test how such a pattern could form corners.
Why the Cubes Matter—and What Remains Unknown
Bare-nosed wombats place their faeces on prominent features such as rocks and logs to communicate with one another. The reason wombats evolved to produce cube-shaped faeces remains to be fully understood.
The appearance of the faeces may also offer a clue to hydration: wombat faeces can look less cubic in wetter conditions. That makes their shape a possible indicator of hydration, rather than a definitive measure.
