Among the many, world-famous, cute critters of the world, koalas are some of the most loved. Often called koala bears, it is commonly known now that they are, in fact, not bears. These lovable creatures are marsupials (along with kangaroos) and so have the pouch to carry their young. Another well-known fact about koalas is what they eat—eucalyptus, and lots of it. In fact, koalas almost exclusively eat eucalyptus. Now, with these plants being their sole diet, one would think that as soon as a joey was old enough, it too would begin feasting on eucalyptus. However, koala joeys actually do not have the capability to digest eucalyptus. So how is it that they get this ability? While the answer makes sense, you may not be able to look at koalas quite the same after.

The problem—koala joeys do not have the enzymes or gut bacteria in their stomach to digest eucalyptus (and, clearly, they are going to be eating eucalyptus). The solution—adult female koalas will pass on these bacteria to their joeys. The method—transfer these bacteria from “pap” (that’s right, special fecal matter from the mother…special poop). Now it is a different texture and color than the normal koala poop, changing to more of a paste than solid, but it does still come out of the same area. This “pap feeding” begins for joeys shortly after leaving the mother’s pouch, and allows for the joey to eventually transition from its mother’s milk to eucalyptus leaves. Eucalyptus leaves have a high concentration of tannins, which create complex chemical structures with protein, making them hard to digest in mammals. However, two types of bacteria in koala guts have been found, streptococci and enterobacteria, which seem to be the stars in helping digest these complex chemical structures. By sharing some “special meals” of pap, these bacteria get passed from the mother koala gut to the joey koala gut.

And for a little extra side snack of odd, it has even been found that koala joeys can induce this pap production from female koalas, even ones that are not their mothers.

The Bite-Sized Takeaway:

• The Problem: Koala joeys lack the gut bacteria to break down eucalyptus (as tannins combine with proteins to create complex, indigestible structures).
• The Solution: Specialized bacteria (Streptococci and Enterobacteria) are able to break down those chemical complexes.
• The Method: A “bacterial transplant” via maternal pap (specialized fecal matter) that gives joeys the tools they need to survive off eucalyptus.

Scientific Papers

Osawa, R., Blanshard, W., & Ocallaghan, P. (1993). Microbiological Studies of the Intestinal Microflora of the Koala, Phascolarctos-Cinereus .2. Pap, a Special Maternal Feces Consumed by Juvenile Koalas. Australian Journal of Zoology, 41(6), 611. https://doi.org/10.1071/zo9930611