Wombats Poop in Perfectly Shaped Cubes

Have you ever wondered what the strangest bathroom habit in the animal kingdom might be? Here is a strong candidate: somewhere in the forests and grasslands of Australia, a stocky, burrowing marsupial is producing droppings shaped like dice. Not roughly cube-like. Not vaguely angular. Genuinely, measurably cube-shaped, with flat faces and sharp corners. The wombat is the only animal on Earth known to do this.

Researchers had known about wombat cube droppings for years, and the obvious guess was that the animal's intestine must be shaped like a cookie cutter — square at the very end, stamping out cubes as the waste passed through. It made intuitive sense. It was also completely wrong. In 2018, a team of scientists, including engineer Patricia Yang, dissected wombat intestines and found something nobody expected: the intestine was round the entire way through, just like in any other mammal. There was no mould. No stamp. No square-shaped exit at all.

If the tube was round, the answer had to be hiding somewhere else. The researchers found it in the walls of the intestine itself. Along the final stretch of the wombat's digestive tract, the tissue varies in thickness and stiffness — some sections stretch easily, while others resist stretching and stay relatively rigid. As waste moves through, it gets squeezed unevenly, bulging out where the wall is soft and staying flat where the wall is firm. Over a long enough stretch of intestine — about ten times longer relative to body size than in humans — those uneven squeezes gradually press the material into flat-sided, sharp-edged cubes. It is closer to slowly folding dough into a block than stamping it with a mould.

This is not just a strange party trick of nature — it serves a real purpose. Wombats are territorial, and they mark their territory by leaving droppings on top of rocks, logs, and raised surfaces, often in places other animals would have trouble reaching. A round pellet, like a marble, would simply roll off. A cube stays exactly where it is placed. The unusual shape is, in effect, a stable little signpost that says: this ground belongs to someone.

It turns out that one of the animal kingdom's oddest party tricks is also a small engineering marvel — built not from a mould, but from the careful, uneven give of living tissue. Next time you spot a perfectly square little block sitting on a rock somewhere in the Australian bush, you will know exactly how it got there.