If you’ve ever looked at a koala reading book, you’ll know that koalas are rather unique creatures. They evolved from a common ancestor with the wombat, but unlike this ground-dwelling creature, they headed up into the trees to live, around 20 million years ago. 

When Australia’s climate became drier and the rainforests began to decline (around 15 million years ago), eucalyptus trees began to spread. Over time koalas adapted to a diet of eucalyptus leaves, and still live on them today. But why do they love this diet so much? Let’s find out.

Eucalyptus galore

Did you know that eucalyptus leaves contain toxins which make them inedible to most creatures? Over millions of years, koalas have become specially adapted to break down these toxins, meaning they are able to feast on the leaves without any adverse effects. 

Their digestive systems contain a long caecum (pronounced see-kum), which is a part of the large intestine. This is filled with specialised bacteria that enables them to break down the toxins into harmless components. In addition, they have lots of a particular liver enzyme (a protein that speeds up chemical reactions) that further detoxifies the leaves. The poisons are then excreted in their poop. 

‘No drink’

Another reason koalas love eucalyptus leaves so much is because they contain so much water; between 75-85% of the leaf is water. In fact, the name ‘koala’ comes from a word in the Dharug Aboriginal language that means ‘no drink’, because they are rarely seen drinking from fresh water sources. 

Fussy eaters

Koalas may be specially adapted to eat leaves that are poisonous to most other animals, but they are also very fussy eaters. They choose only certain species of eucalyptus trees - the ones with toxins that their digestive systems can break down. In fact, out of 700 different species of eucalyptus trees, koalas eat the leaves of fewer than 50. They also choose wisely - the leaves at the tops of the trees contain more water and nutrients, so they tend to feast on those. 

Preparing for poison

When baby koalas are born, they have no way to process the poisons that are in eucalyptus leaves. Before they can be weaned, they must obtain the necessary gut bacteria to be able to break down the toxins in their diet. 

At around six months old, a joey starts eating pap - a soft substance that is excreted from its mother’s anus. This is not only nutritious, but also rich in the bacteria the joey needs to digest eucalyptus. The baby will feed on this until it is about seven or eight months old, when its teeth begin to grow and it can munch on fresh leaves. 

The Koala Who Could

If your kids enjoy Rachel Bright and Jim Field’s koala picture book, The Koala Who Could, why not take them to see the stage production this season? The family-friendly koala show retells the charming story of Kevin the koala with singing, dancing and puppetry, and is currently touring the UK. Book tickets today at your local theatre.