The main food source for koalas is eucalyptus leaves. These Australian marsupials are highly specialized feeders, with over 600 types of eucalyptus trees existing in the wild, but they primarily consume leaves from just a few species. Eucalyptus leaves are tough and have low nutritional value, making it necessary for koalas to eat large quantities to meet their energy needs. Additionally, the leaves contain toxins that most animals cannot tolerate, but koalas have developed adaptations to detoxify them. Their diet is crucial to their habitat and survival, showcasing the unique relationships between species and their environments.