Why does a koala eat eucalyptus leaves?

Koalas eat eucalyptus leaves because they are specially adapted for this purpose. Koalas live in eucalyptus trees and eat only a few types of gum leaves from which they get all nutrients and water requirements. They also occasionally eat the gum tree blossoms. Eucalyptus leaves are tough, toxic and low in nutrition, but the koala's digestive system is able to remove the toxins, filtering them out by the liver. The caecum, which is similar to the human appendix, changes the eucalyptus leaves into digestible nutrients.

While there are hundreds of different eucalyptus species in Australia, koalas eat from only about 60 of the species, consuming about half a kilogram of eucalyptus leaves every day.