Why do koalas sleep so much?

KohakuHave you noticed that the koalas at the zoo always seem to be asleep? There is a good reason for that.

The answer in 30 seconds

First, let me give you the answer in 30 seconds.

Koalas sleep a lot because their main food, eucalyptus leaves, gives them very little energy. The leaves are full of fiber and contain substances that can be toxic, so they take a long time to digest. Koalas are thought to save energy by sleeping or resting for about 18–22 hours a day.

A koala curled up asleep in the fork of a tree branch — A koala sleeping with its body tucked into the fork of a branch.Photo: Alex Proimos from Sydney, Australia / CC BY 2.0 / Wikimedia Commons

Resting in the trees most of the day

Koalas spend about 18–22 hours a day sleeping or resting, sitting in the fork of a tree branch. San Diego Zoo also explains that they rest this long to save energy. They are mostly active at night, and they spend much of their waking time eating leaves.

Figure: A koala's day (resting time and active time)

Bar lengths are approximate.

Eucalyptus: a low-nutrient leaf

Their main food, eucalyptus leaves, is full of fiber (the tough strands in plants) and low in nutrients. The leaves also contain substances that are toxic to most animals. Koalas have a long cecum (part of the large intestine), and with help from the bacteria in their gut, they digest these leaves slowly.

KohakuLiving on leaves alone is harder than it looks, isn't it?

Saving energy by staying still

A research paper from Australia explains that the low nutrition of eucalyptus, combined with the work of dealing with its toxins, limits the energy koalas can use. That is why they are thought to save energy, and help their digestion, by moving little and resting for long periods.

Figure: Why koalas rest for so long

Wild koalas move a little more

Still, koalas are not asleep all the time. A study of wild koalas using accelerometers (small devices that record movement) attached to collars found that they were active for about 5–6 hours a day on average, ranging from 4.5 to 7 hours depending on the koala. Resting time also changes with the season and from koala to koala.

Want to know more?

A koala's hand has two thumb-like fingers that face the others. Together with sharp claws, they let it grip branches firmly.
There are more than 600 kinds of eucalyptus, but koalas prefer to eat only a little over 30 of them.
A baby grows in its mother's pouch for about 6 months. After that, it is thought to eat its mother's soft droppings to take in the bacteria that digest eucalyptus.

KohakuA koala's long naps aren't laziness. They are a wise way of making the most of very little energy.

Quick quiz: test yourself

What is the main reason koalas sleep so much?

Show the answer

Eucalyptus toxins make them sleepy
Their food gives little energy
So they don't fall from trees

Their food gives little energy Eucalyptus leaves give little energy and take a long time to digest. Koalas are thought to rest for long hours to save energy.

Sources

KoalaSan Diego Zoo Wildlife Alliance
Activity Patterns of Free-Ranging Koalas (Phascolarctos cinereus) Revealed by AccelerometryPLOS ONE
KoalaAustralian Museum

This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.