Koalas are known for their exclusive diet of eucalyptus leaves, a food source posing significant challenges due to its toxic compounds and low nutritional content. This specialized diet often raises questions about their unusual eating habits, particularly if they consume their own waste. Young koalas, called joeys, consume a special substance called “pap” produced by their mothers, which is not ordinary feces. This practice is fundamental to their development, enabling survival on an otherwise harmful diet.
The Koala’s Specialized Diet
Koalas are herbivores, feeding almost entirely on eucalyptus leaves. These leaves are fibrous, low in protein, and contain chemical compounds toxic to most other animals. To manage this challenging diet, koalas have evolved specialized digestive adaptations, including a very long caecum, up to 200 centimeters long. This large organ houses millions of bacteria that break down tough fibers and detoxify harmful chemicals.
Despite these adaptations, adult koalas absorb only about 25 percent of the fiber they consume. The detoxification process requires substantial energy, contributing to their sedentary lifestyle and long sleep periods (18 to 22 hours daily) to conserve energy. While adult koalas produce dry, pellet-like feces, mothers produce “pap” for their offspring. Pap is a soft, greenish, semi-liquid substance, distinct from regular adult droppings.
A Crucial Nutritional Step
Pap is produced by the mother for her joey, typically when the joey is 5 to 7 months old and emerges from the pouch. This substance is a specialized output from the mother’s caecum, rich in essential microbes and nutrients, not regular fecal matter. The joey stimulates the mother’s cloaca with its mouth to encourage the release of pap, which often appears after the discharge of normal fecal pellets.
Pap consumption is a necessary developmental milestone for joeys, transitioning them from milk to a solid eucalyptus diet. Pap contains live bacteria, including tannin-protein-complex-degrading enterobacteria, transferred from the mother’s digestive system. These microbes colonize the joey’s immature gut, establishing the microbiome needed to break down toxic compounds and digest fibrous eucalyptus leaves.
Without this microbial inoculation, joeys cannot process their adult diet, making pap consumption fundamental for their survival and transition to independent feeding. The joey’s microbiome gradually shifts over several months to resemble that of an adult, becoming fully adapted by about one year of age.