Here’s how — and why — wombats poo cubes

Famous Tasmanian exports – Princess Mary and an animal that poos cubes. Picture: Getty Images

“We opened those intestines up like it was Christmas.”

Gruesome as that quote in Science News sounds, it’s a compelling insight into how much scientists are fascinated by wombats. Or at least fascinated by wombat poo, which is cube-shaped.

Yes, the Australian marsupial, despite having a round anus, literally s**ts bricks. Look:

Exhibit A. Picture: Bjørn Christian Tørrissen/Wikimedia Commons

The American Physical Society Division of Fluid Dynamics also looked at it — closely — at its annual meeting in Atlanta.

A team, led by Georgia Institute of Technology’s Patricia Yang, her colleagues Miles Chan and David Hu, and University of Tasmania’s Scott Carver, were presenting their findings on how wombats actually do this.

“In the built world, cubic structures are created by extrusion or injection molding,” the team said, “but there are few examples of this feat in nature.”

To study it, they needed some wombats, and the Tasmanian roadside provided two unfortunate specimens, euthanised by vets after they had been hit by cars.

Then, it was Christmas time. To see what was really going on in the wombats’ digestive tract, the team emptied it and inserted a long balloon in it, then inflated the balloon.

It’s in the final 8% of poo labour that the wombats’ faeces change from liquid state to solid cubes with 2cm edges.

The study, published in Bulletin of the American Physical Society, found that the balloon showed that a wombats’ intestinal wall has “azimuthally varying elastic properties”.

“By emptying the intestine and inflating it with a long balloon, we found that the local strain varies from 20% at the cube’s corners to 75% at its edges,” the team said.

“Thus, the intestine stretches preferentially at the walls to facilitate cube formation.”

That discovery could even have some real-world use for humans, in manufacturing real brick shapes directly out of soft tissues rather than moulding or cutting them.

The real question is, why do wombats poo cubes?

So they don’t roll away, silly. Because everyone knows that once wombats have done their business, they stack it up to attract other wombats.