What do koalas eat? Koala diet explained

 ​Koalas are one of the most specialised eaters in the animal kingdom. Their diet consists almost entirely of eucalyptus leaves, selected from around 30 of the more than 600 eucalypt species found across Australia. These leaves are tough, fibrous and toxic to most animals, yet koalas have evolved a remarkable digestive system that allows them to thrive on a food source almost nothing else can stomach 

Read on to learn about the vital role of diet in koala health and discover how you can contribute to their wellbeing.

You can support our free wildlife veterinary care by donating directly at our donation page.  When you donate to us, you are helping us get koalas back to the wild and back to eating leaf in their natural environment.

What is special about a koala's diet?

Koalas rely almost entirely on eucalyptus leaves for food, even though these leaves are tough, low in nutrients, and difficult to digest (Lawler et al., 1998). They also contain natural chemicals called phenolics and terpenes, which are toxic to most animals (Foley, Iason, & McArthur, 1999).

​So how do koalas survive on a diet that most animals avoid?

• They have developed special adaptations that allow them to process eucalyptus leaves efficiently. One adaptation is their slow metabolism, which helps them conserve energy while digesting this tough diet (Ellis & Bercovitch, 2011).  That's one of the reasons they sometimes look sleepy.
• Another remarkable feature is their unusually long caecum - a part of their digestive system that is the longest relative to body size of any animal. This organ is home to special bacteria that break down the tough plant material, turning it into nutrients the koala can absorb (Osawa, 1990).

• Research shows that koalas carefully choose their leaves based on nutritional content and the levels of natural plant chemicals, known as secondary metabolites, which can affect digestibility and taste (Marsh, Wallis, & Foley, 2003).
• ​​They also tend to prefer leaves from older eucalyptus trees, which are believed to have higher protein content, making them a more nutritious option (Ellis, Melzer, & Carrick, 2002). This pickiness isn’t just about preference - it’s a crucial survival strategy that helps them get the most out of their limited diet.
  

​By being selective, koalas have adapted to live on a diet that nearly every other animal cannot. 

What else do koalas eat?

In conditions such as drought or lack of preferred eucalyptus species, koalas may even turn to exotic plant species introduced in their habitats. Plus they may like to eat  specific types of bark and wood which likely reflects the mineral content within these substances, offering a glimpse into their dietary adaptability under ecological pressures.

Koalas, rather than being a fan of eucalyptus, also eat other species too if required.  They might eat other plants like Corymbia, Melaleuca, Causarina and Angophora, all of which are directly related to Eucalyptus, particularly when the situation is urgent.

More koala facts are here

Favourite Leaf of Koalas - What do they enjoy eating?

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Koalas' love for specific eucalyptus leaf is well-known. However, their preferences can change greatly depending on the region due to variations in eucalyptus species availability across Australia.

​Still, several eucalyptus species regularly are enjoyed:
 
1. **Eucalyptus camaldulensis** (River Red Gum): Widespread and a koala favorite.
 
2. **Eucalyptus tereticornis** (Forest Red Gum): Frequently found in koala diets.
 
3. **Eucalyptus microcorys** (Tallowwood): A popular choice for koalas in New South Wales and Queensland.
 
4. **Eucalyptus punctata** (Grey Gum): A frequent constituent of the koala's diet in New South Wales and Queensland.
 
5. **Eucalyptus viminalis** (Manna Gum): A favored food source, particularly among koalas in Victoria and South Australia

6.  ** Swamp Gum (Eucalyptus ovata), , River Red Gum (Eucalyptus camaldulensis), Blue Gum (Eucalyptus leucoxylon), Long-leaved Box (Eucalyptus goniocalyx) and Brown Stringybark (Eucalyptus obliqua) - All South Australian favorites!!

Koala's Sense of Smell

Koalas demonstrate a remarkable ability to select eucalyptus leaves based on nutritional value, actively choosing leaves with higher protein content and lower levels of defensive chemicals such as tannins and phenolic compounds (Marsh, Wallis & Foley, 2003).

Koalas have also evolved highly effective water conservation mechanisms.

In their often arid habitat, they obtain the majority of their hydration directly from eucalyptus leaves, though they will drink free water when it is available and will actively seek alternative water sources when needed (Ellis & Melzer, 2003).

​Current research continues to expand our understanding of koala hydration needs. Read more about koalas and water here

Do Koalas Eat Soil?

​While eucalyptus leaves make up the majority of a koala's diet, koalas also consume soil, particularly from termite mounds. Known as geophagy, this behaviour is thought to provide essential minerals and digestive enzymes that eucalyptus leaves alone cannot supply.
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Interestingly, sick koalas have been observed eating soil more frequently, leading researchers to suggest they may be self-medicating. This has practical implications for wildlife care; facilities now routinely offer soil in bowls to unwell koalas to support their recovery (Gillett et al., 2019). Some researchers also suggest that clay-rich soils may help koalas detoxify compounds found in their eucalyptus diet (Barker et al., 2005).

The Implications for Koalas in a Hot Climate

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Koalas have a highly specialised diet, which gives them an advantage by reducing competition for food. However, this comes with challenges as eucalyptus leaves are low in nutrients and contain natural toxins that koalas must process to survive.

Research suggests that climate change may make eucalyptus leaves even less nutritious, putting koalas at greater risk (Moore et al., 2010).  

The water content in fresh eucalyptus leaves can provide a large portion of a koala’s hydration; studies show koalas obtain approximately 74–81% of their daily water intake from leaf moisture alone (Mella, Ward, & McArthur, 2019).  But when eucalyptus trees are exposed to heat and drought - and with climate change this is now happening more than ever, so leaves begin to lose moisture - a process known as desiccation. You can think of it like a sponge drying out. At first, the leaves may still feel soft and moist, but over time they become drier and less able to hold water.

Scientists measure desiccation time to understand how long it takes for leaves to dry out once water is no longer available. In one study looking at a range of eucalyptus species, some leaves lost their moisture in just 4 days, while others took up to 14 days to fully dry (Blackman et al., 2019).

This matters because:

• Trees with a short desiccation time lose water quickly and become poor sources of hydration for koalas.
• Trees with a longer desiccation time hold onto water longer, giving koalas more time to access moist, hydrating leaves  especially during heatwaves or when rainfall is low.

Leaves that dry out quickly are simply less helpful to koalas, especially when droughts last for weeks or months.   So do koalas need water?  Yes - read more here. 

Science has debunked the theory that koalas are not water drinkers. 

This problem of lack of moisture in leaf is an important example of how climate extremes impact wildlife: the eucalyptus tree can endure drought by dropping leaves, but the koala then faces a landscape of crunchy, dry leaves that can’t sustain them. Understanding eucalyptus leaf desiccation helps explain why, in tough times, koalas need a helping hand (or a helping sip) to quench their thirst. Koalas will drink water if the leaf cannot sustain their hydration levels. 
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If you find a koala that appears lethargic, dehydrated or injured, seek veterinary advice immediately. A continuously drinking koala needs help.  Our team provides professional wildlife veterinary care for koalas across South Australia.

 -  Found a koala on the ground - what you need to know
-   Contact numbers for us and rescue groups

How can you help koalas today?

Adelaide's summers are getting hotter and koalas are suffering for it. Heat stress and dehydration can be fatal without prompt veterinary treatment, and during heatwaves our clinic sees a dramatic increase in koalas needing urgent care.
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Since 2014 Adelaide Koala and Wildlife Centre has provided free professional veterinary treatment to over 15,000 native animals  - five days a week, every week. Every dollar donated goes directly to the clinical care that gives koalas and native wildlife a second chance.

Help Us Treat Heat-Stressed Koalas

During Adelaide's hottest days our clinic sees a surge in heat-stressed and dehydrated koalas needing urgent care.

Donate Today

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References:
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Cork, S. J., & Sanson, G. D. (1990). Digestive adaptations of the koala. Australian Natural History, 23(7), 498-503.

Ellis, W. A., & Bercovitch, F. B. (2011). Body size, reproductive phenology and life history in Koalas. Journal of Mammalogy, 92(1), 102-112.

Ellis, W. A., Melzer, A., & Carrick, F. N. (2002). Breeding dynamics of koalas in open woodlands. Wildlife Research, 29(1), 19-25.

Foley, W. J., Iason, G. R., & McArthur, C. (1999). Role of plant secondary metabolites in the diet of the koala. In: Nutrition for the 21st Century (pp. 45-58). Federation of Asian and Oceanian Biochemists and Molecular Biologists (FAOBMB).

Gillett, A., & Hanger, J. (2019). 32 Koala. Current Therapy in Medicine of Australian Mammals, 463.

Lawler, I. R., Stapley, J., Foley, W. J., & Eschler, B. M. (1998). Ecological example of conditioned flavor aversion in plant–herbivore interactions: effect of terpenes of Eucalyptus leaves on feeding by common ringtail and brushtail possums. Journal of Chemical Ecology, 24(1), 1-9.

Lunney, D., Crowther, M. S., Wallis, I., Foley, W. J., & Lemon, J. (2012). Koalas and climate change: a case study on the Liverpool Plains, north-west New South Wales. In Wildlife and Climate Change: Towards Robust Conservation Strategies for Australian Fauna, 150.

Marsh, K. J., Wallis, I. R., & Foley, W. J. (2003). The effect of inactivating tannins on the intake of Eucalyptus foliage by a specialist Eucalyptus folivore (Pseudocheirus peregrinus) and a generalist herbivore (Trichosurus vulpecula). Australian Journal of Zoology, 51(1), 31-42.

 Moore, B. D., Wallis, I. R., Marsh, K. J., & Foley, W. J. (2004). The role of nutrition in the conservation of the marsupial folivores of eucalypt forests. In Conservation of Australia’s forest fauna (pp. 549-575). Royal Zoological Society of New South Wales.

Moore, B. D., & Foley, W. J. (2005). Tree use by koalas in a chemically complex landscape. Nature, 435(7041), 488-490.

Osawa, R. (1990). Formation of a clear zone on tannin-treated nutrient agar by a Streptococcus sp. isolated from feces of koalas. Applied and Environmental Microbiology, 56(3), 829-831
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Phillips, S., & Hopkins, M. (2007).  Tweed Coast Koala Habitat Studyhttps://www.tweed.nsw.gov.au/files/assets/public/documents/environment/native-plants-and-wildlife/koala-habitat-study.pdf

Understanding koala life - Department for Environment and Water
Source: Strahan, Ronald (Ed) (1998) Complete Book of Australian Mammals, Australian Museum. Koala scent gland
https://cdn.environment.sa.gov.au/environment/docs/pa-fact-koalalife.pdf

Ellis, W., Melzer, A., Carrick, F., & Hasegawa, M. (2010). Tree use, diet and home range of the koala (Phascolarctos cinereus) at Blair Athol, central Queensland. Wildlife Research, 29(3), 303–311v

Mella, V. S. A., Ward, S. J., & McArthur, C. (2019). Needing a drink: Rainfall and temperature drive the use of free water by a threatened arboreal folivore. PLOS ONE, 14(5), e0216964. 
Mella, V. S. A., Orr, C., & Hall, L. S. (2020). An insight into natural koala drinking behaviour. Ethology, 126(8), 858–863.