Koalas eat leaves, with eucalyptus being the most prominent staple in their diet. Koalas have very strong jaws, allowing them to chew tough, fibrous leaves. Eucalyptus leaves are very low in nutrition, and they contain a toxin that is filtered out through the digestive system. Koalas use their keen sense of smell to differentiate between leave types, and determine how much of the toxin they contain.
A baby koala, or a joey as it is called, nurses on milk while it lives in its mother's pouch for around six months. After emerging from the pouch, the joey lives on its mother's back for roughly six more months, subsisting on both milk and eucalyptus leaves. After approximately one year, the joey is weaned off of milk.
Koalas only eat 50 species of eucalyptus, out of the 700 in Australia. Their sharp claws and strong limbs allow them to climb tree trunks. Koalas have tails with thick padding, which helps them to sit in trees for hours at a time. They have four fingers and an opposable thumb on each hand for gripping the branches. They tend to be solitary creatures, and males mark their territory by rubbing a scent gland against trees.