What do koalas eat and why?

Koalas are herbivorous, living almost exclusively on eucalyptus leaves. These leaves supply them with most of the water they need, although they have been observed drinking water as well. They also occasionally eat the gum tree blossoms.

Eucalyptus leaves are tough, toxic and low in nutrition, but the koala's digestive system is capable of removing the toxins, filtering them out by the liver. The caecum completes the process by changing the eucalyptus leaves into digestible nutrients. The caecum is similar to the human appendix.

Baby koalas, called joeys, drink mother's milk during their first 6-7 months of life. After 30 weeks, the mother produces a substance called pap. This substance is actually a specialised form of the mother's droppings which, having passed through her digestive system, give the joey the enzymes it needs to be able to start digesting the tough gum leaves, making an easier transition for the baby koala to start eating eucalyptus leaves.