One of Australia’s most iconic animals is known the world over for their cute faces and soft fur. But what may come as a surprise is that these gentle creatures are among the only few who can safely consume leaves that are toxic to many animals.
Their diet is composed mainly of eucalyptus leaves from eucalyptus trees commonly called gum trees. They grow in tropical and temperate environments in the southern hemisphere. Numerous varieties of eucalyptus trees are found in Australia. However, koalas only eat certain species of eucalyptus. Out of the roughly 650 species found in Australia, they only prefer 35 of them
Koalas eat around one to two pounds of these leaves each day. But they are known to consume even more when they are lactating.
These eucalyptus leaves are one of the most poisonous plants for many animals. The leaves with their leathery exterior and dark green color, are heavy on fiber. Around 18% of these are composed of fiber with around 50% water. But it also contains a toxic cocktail of chemicals that are believed to serve as the plant’s protection against leaf-eating insects. This is why eucalyptus oil is found in many insect repellant lotions and sprays. Aside from insects they can be lethal to larger animals like dogs, cats, and horses among many others.
So how can koalas eat these deadly leaves? The answer is in their gut
Specialized Diet And Digestive System
To process their unique diet, koalas have a specially adapted kind of digestive system. A particular organ called caecum that’s over 6 feet long (the longest in animals) helps digest fibrous eucalyptus leaves through fermentation. It also aids in detoxifying the leaves. Special microbes found in the koalas’ digestive tracks, also help break down the poisonous chemicals in their diet. But what’s even more fascinating is that these microbes are also passed down from mother to baby through the pap.
The pap is a specialized form of droppings or some consider feces, which allow baby koalas to transition from milk to eucalyptus leaves. It gives them the natural defenses that will allow them to eat these toxic leaves.
Since eucalyptus leaves are incredibly fibrous, koalas spend most of their days chewing. This is why you’d almost always find them chewing, all day, atop trees.
Their teeth, like their digestive system, are adapted to their unique diet. For instance, sharp front incisors help koalas cut the leaves off of trees and branches. Their back teeth, on the other hand, are shaped in such a way that allows them to cut the leaves into tiny parts instead of just crushing them. Their powerful jaws help turn these seemingly-tough fibrous leaves to a fine paste in the mouth.
Eucalyptus leaves are very high in fiber but have low nutrient and caloric content. And since their food provides little energy, koalas tend to be lethargic. They also sleep up to 20 hours per day so they can conserve their energy.
This is why you’d often see these gentle creatures moving slow and almost always, sleeping with their babies behind some tree branch. Contrary to what others believe, it is not because eucalyptus makes them intoxicated. It is just that eucalyptus leaves have very low caloric content in general and thus provide very little energy. Some scientists also believe that aside from having a nutrient-poor diet, the koala's long and specialized digestion process uses up what little energy they get from their food.
The koala’s drinking habits have long baffled scientists and locals since they seem to not drink water at all in the wild. In fact, the word koala was thought to mean “no drink” in the Australian aboriginal language. They are only seen drinking water when they are sick or under severe heat stress.
Many previously believed that they only get their water from the leaves they eat and when they munch on eucalyptus leaves drenched with rainwater.
But scientists have recently found that koalas also get water by licking down tree trunks during rainfall. The phenomenon called "stemflow" gives koalas access to much-needed hydration. Koalas were observed collecting stemflow from tree trunks during a study of koalas in the Australian wild from 2006 to 2019.
This discovery, according to scientists, is a crucial breakthrough that may help conservation efforts.