Wombats squeeze out cubes, and their guts are the mould 🧊

Wombats are the only known animals that produce cube-shaped droppings. The feat is not the work of a mould at the exit, but of the animal's own intestines, where the waste is gradually shaped into a cube as it travels. ^[1]

Why a cube is useful

Wombats use their droppings to mark territory. Cubes do not roll off rocks or logs the way spheres would, so they stay put and communicate ownership. The shape is a functional adaptation, not an accident. ^[2]

The gut as a mould

A 2018 study found that the wombat intestine is not a uniform tube. It has regions of stiffer and softer tissue arranged in a pattern. As waste moves through, these varying tensions press the material into a cube. The corners form first, then the flat sides. ^[1]

The researchers used a combination of dissection, imaging and mechanical testing to show that the cube shape emerges gradually along the last metre or so of the intestine. The process is passive, driven by the gut's own structure rather than by muscles actively cutting corners. ^[1]

Not just any cube

• The droppings are roughly 2–3 cm across and have rounded edges, not sharp ones. ^[1]
• The cube shape is consistent across the three wombat species. ^[2]
• Other herbivores with similar diets produce cylindrical or spherical pellets. ^[1]

What it tells us

The wombat gut shows how soft tissue can act as a mould without being rigid. Engineers have taken interest, because the same principle could inspire new ways to shape materials in manufacturing. For biologists, it is a reminder that evolution can solve a problem in an unexpected place. ^[3]

The finding was published in 2018 by a team at the Georgia Institute of Technology, and it remains the clearest explanation for the wombat's famous droppings. No other animal is known to produce cubes this way. ^[1]