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Question of the Week: Why Do Wombats Poop Cubes?

By Arendse I Lund, on 14 February 2018

 

A wombat waddling along (Image: © Jack Ashby)

With pudgy little legs and a determined waddle, wombats are amongst Australia’s cutest marsupials. I mean, have you ever seen a wombatlet (not the technical term, unfortunately) sneeze? There’s lots to love about wombats—including their cube-shaped poop.

Wombat faeces—not a snack treat (Image: Bjørn Christian Tørrissen)

This odd wombat feature has sparked a lot of gleeful speculation. The prevailing thought is that these six-sided excrements are caused by a combination of the digestion time, the shape of the large intestine, and the dryness of the resulting fecal matter.

Wombats have a slow digestive system—it takes up to 2.5 weeks for food eaten to make its way down the alimentary canal, through the stomach, small intestine, and finally out the anus as fecal matter. (On the scale of animal defecation time, wombats aren’t even in the running. One snake was recorded as “holding it” for 420 days.)

A common wombat, or Vombatus ursinus, skull with large teeth for masticating grasses and roots, and a skeleton with large front claws for digging (Images: Grant Museum of Zoology, Z68 and Z67)

After being processed by the stomach, the digested matter transverses the large intestine, which is a long tube-like organ with ridged sides. These ridges may help to break the matter into compact sections. Since the final part of the intestine is much smoother, these cubed sections retain their shape all the way to the anus.

A wombat’s long digestive time means that this matter becomes condensed and, ultimately, dry as the nutrients are extracted. Wombats have some of the driest faeces amongst mammals and, it turns out, it’s a handy evolutionary trait. Wombats use their droppings to mark territory; with a propensity to defecate on logs and other elevated objects, cubes won’t roll off, unlike cylindrical droppings. As wombats drop between 80 and 100 scats a day, it would be a pain if they, well, scattered.

 

According to Jack Ashby, Manager of the Grant Museum of Zoology, “Another thing to note about wombat poo is that since wombats have backwards-facing pouches, larger wombatlets end up spending a lot of time with their faces in poo. It has been suggested that this is an important way that they gain helpful gut bacteria that they need to digest the wombat diet of tough Australian grasses.”

If you want to see fake wombat faeces in action, Robyn Lawrence created a video demonstrating a wombat’s digestive system. She uses Jell-O to illustrate the forming and squeezing of the food into cube shapes, which then passes unchanged through the colon and out the fake anus.

So no, the wombat rectum isn’t square.

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Further Reading:

Menkhorst, P. A Field Guide to the Mammals of Australia. South Melbourne: Oxford University Press, 2001.

Triggs, Barbara. The Wombat: Common Wombats in Australia. University of New South Wales Press, 2002.