Koalas

The oil found in eucalyptus leaves is poisonous to many mammals. This poison is a chemical defense mechanism used by eucalyptus trees against their enemies. Yet there is a very special living being that gets the better of this mechanism and feeds on poisonous eucalyptus leaves: a marsupial called the koala. Koalas make their homes in eucalyptus trees while they also feed on them and obtain their water from them.

Like other mammals, koalas also cannot digest the cellulose present in the trees. For this, it is dependent on cellulose-digesting micro-organisms. These micro-organisms are heavily populated in the convergence point of small and large intestines, the caecum which is the rear extension of the intestinal system. The caecum is the most interesting part of the digestion system of the koala. This segment functions as a fermentation chamber where microbes are made to digest cellulose while the passage of the leaves is delayed. Thus, the koala can neutralize the poisonous effect of the oils in the eucalyptus leaves.