Koalas only eat the leaves of one kind of tree: the eucalyptus, or gum tree. Eucalyptus leaves are tough, full of oils, and slightly poisonous to most animals. Koalas have a special long gut that breaks the leaves down very, very slowly. That is one reason they need so much sleep - digesting is hard work.
There are over 700 kinds of eucalyptus tree, but most koalas only eat from a few of them. A koala can recognise its favourite leaves by smell alone. They eat about half a kilogram of leaves a day - that's the weight of a small bag of sugar in salad.
A baby koala is called a joey, just like a baby kangaroo. It lives in its mum's pouch for about six months. After that, it climbs onto her back and rides around like a small, fuzzy backpack until it is old enough to look after itself.
Koalas have very strong claws and rough pads on their paws, which help them grip tree trunks like climbers wear special shoes. They have two thumbs on each front paw - one extra compared to humans - to help them hold branches tightly. They are excellent climbers but a bit clumsy on the ground.