Why do koalas sleep so much?

Answer: Their low-energy eucalyptus diet

Their brains need extra rest — Wrong. A koala's brain is actually quite small for its body size, so it does not need extra rest for brain function. The long sleep comes from a eucalyptus diet that supplies minimal energy.

They hibernate year-round — Wrong. Koalas do not hibernate; they are active every day, just for very short periods. Their extended sleep is due to their low-calorie eucalyptus diet, not seasonal dormancy.

Their low-energy eucalyptus diet ✓ — Correct! Koalas sleep 18 to 22 hours a day mainly to save energy, because eucalyptus leaves give them very little fuel. The leaves are low in protein and energy, they contain toxic compounds that cost energy to break down, and they are so tough and fibrous that digestion takes days. A slow metabolism helps the koala conserve every calorie, and its unusually small brain also saves energy. The animal feeds mostly at night and relies on special gut bacteria to detoxify the leaves, so its energy budget is so tight that it can only be active for short periods.