Why do koalas sleep so much?

Koalas sleep up to 18-20 hours a day to conserve energy, as their diet consists mainly of eucalyptus leaves, which are low in nutrients and difficult to digest. Digesting these leaves requires a lot of energy, so koalas minimise their activity to ensure they extract the maximum nutrients. Their large, specialised caecum contains bacteria that break down the tough cellulose in eucalyptus. This slow lifestyle helps koalas thrive on a diet that would be insufficient for many other animals.