Koala facts

• The word "koala" originates from the dharug Aboriginal word ‘koolah’, which roughly translates as ‘no drink’ or ‘no water’.¹
• In the Australian bush, koalas rarely drink water as they get most of the H20 they need from eating fresh eucalyptus leaves.
• There is only one species of koala in the whole world; they are the only surviving member of their family. Koalas’ closest living relative is the common wombat.²
• Koala babies, known as joeys, are born just five weeks after conception. New-born joeys are only 2cm long – about the same size as a jellybean. 
• Koalas are not social animals and prefer a solitary lifestyle in the wild. Once young joeys mature, they usually leave their mother’s territory and seek out a new home. Koalas are highly territorial animals.
• Koala fur is coarse, like the wool of a sheep.³
• Koalas have two opposing thumbs on each of their hands. They also have two toes fused together on their feet, which they use to comb their fur.⁴
• Koala bears have an excellent sense of smell, which they use to sniff out the most nutritious eucalyptus leaves. They can also detect the whiff of other koalas’ scent markings on trees.
• Koalas sleep for between 18-20 hours every day. Their extraordinary laziness is believed to be an adaptation to their leaf-based diet. They get very little energy from eating eucalyptus leaves, so they need to rest to conserve their energy.
• Koalas are marsupials, and like many other marsupials, they carry their young joeys in pouches. The pouch protects joeys from injury while the mother climbs among trees.  
• Although they usually move around at a relatively slow pace, a startled koala can run on the ground at speeds of up to 30km/h.⁵ If frightened, they can run up a tree in two-metre bounds.⁶

Koalas live in Australia – however, as 70% of this continent consists of either arid or semi-arid land, koalas must be choosy about where they make their homes. They tend to be found in the southeast and eastern parts of Australia, along the coastlines of Queensland, New South Wales, South Australia, and Victoria.⁷ There, they inhabit forests and open woodlands close to the coast, particularly those dominated by eucalyptus trees.  They can also be found inland, living in eucalyptus woodlands close to streams and creeks.

Koalas are leaf specialists. Their favourite food is leaves from the eucalyptus tree, but they have also been known to munch the foliage of other plant species. Koalas can even store leaves in their cheek pouches in case they get hungry later in the day.⁸ They eat so much eucalyptus (up to 1kg a day) that they even take on its smell.⁹

Their penchant for eucalyptus is especially unusual, as the leaves contain toxins that can be poisonous and even fatal to other animals when eaten. The leaves are also very tough and rich in fibre, making them difficult to digest. To help them in this task, koalas have a two-metre-long digestive tube called a caecum, in which specialised gut bacteria help them break down the insoluble fibre, as well as the toxins in eucalyptus leaves.¹⁰

In 2018, researchers led by Rebecca Johnson at the Australian Museum Research Institute in Sydney sequenced the complete genome of the koala.¹¹ They found detoxification genes that allow the koala to break down the poisonous compounds in eucalyptus leaves, as well as specialised taste and smell genes that allow the animals to sniff out the most nutritious leaves. Koalas can often be seen sniffing the leaves before they eat them and are quite fussy about the leaves they choose.

There are other aspects to the koala’s diet that are unconventional to say the least. As baby joeys don’t have the gut bacteria that can detoxify the poisons in eucalyptus leaves,  they eat a liquified version of their mother’s faeces – known as pap.¹² The poo acts like a microbial transplant, giving the baby koalas the bacteria they need to allow them to feed on eucalyptus. Baby joeys also drink their mother’s milk both before and during the pap stage.

Koalas are often referred to as bears, but this is a misnomer. Although their scientific genus, Phascolarctos, translates as "pouched bear", koalas are not members of the bear, or Ursidae family.¹³ Koalas are actually more closely related to kangaroos, bandicoots and possums than true bears. Koalas are marsupial mammals, which means that females give birth to relatively underdeveloped offspring. The baby koala, known as a joey, instinctively crawls inside its mother’s pouch where it continues to grow. True bears, on the other hand, are placental mammals, which means that offspring receive nutrients and oxygen via the placenta, allowing the foetus to grow and develop within its mother’s womb for a longer period of time.

Joeys grow and develop in the pouch for about six months. Once strong enough, they climb on their mother’s back where they stay for a further six months, returning to the pouch only to feed.

We know from the fossil record that primitive marsupials inhabited Australia from 55 million years ago.¹⁴ Evidence also suggests that koalas probably separated from wombats around 30-40 million years ago, with the first koala-like animals appearing in the fossil record around 25 million years ago.¹⁵ In total, 15-20 distinct species of koala have been identified.¹⁶ The modern koala, Phascolarctos cinereus, first appeared around 350,000 years ago, and is the only surviving member of the koala family. So what happened to the other species?

The greatest diversity of koala species occurred in the late Oligocene (25 million years ago) and early and middle Miocene periods (23-16 million years ago).¹⁷ At this time, lush rainforests existed in Australia. However around 16 million years ago, the onset of drier conditions meant that the number and size of these rainforests diminished. This resulted in the apparent extinction of at least three koala lineages (Litokoala, Nimiokoala, and Priscakoala).¹⁸ 

Recently, scientists discovered fossils from a new species of koala, which roamed Australia 25 million years ago.¹⁹ The species – Lumakoala blackae – is represented by just by a dozen ancient teeth found in rocks near Alice Springs, a town in the Northern Territory of Australia. The teeth suggest the small, cat-sized koala, weighed between 2.2 and 2.6kg, a lot less than modern koalas, which weigh between 4.1 and 13.5kg. Analysis of the dentures suggest that the tiny koalas probably fed on soft leaves and small fruits, rather than the tough eucalyptus leaves favoured by today’s koala bears. Interestingly, the study also found fossilised teeth from other previously known genera of koalas, Madakoala and Nimiokoala, hidden in the rocks. This suggests that at least three species of koalas were living in the area at the time. Also present were members of the family Ilariidae – huge marsupials that weighed upwards of 200kg and were the largest land mammals in Australia at the time.

Chlamydia is a sexually transmitted disease that is widespread amongst koalas. Amongst mainland koala populations, infection rate varies between 21%–88%.²⁰  Chlamydia can cause painful urinary tract infections, loss of bladder control, blindness, infertility and even death in koalas, with the infection thought to be a major cause of plummeting koala numbers.²¹

Attempts to treat koalas with antibiotics haven’t worked, as koalas appear to suffer serious side effects from these drugs. This is likely due to the fact that broad-spectrum antibiotics wipe out the “good bacteria” in the koalas’ guts that help them break down harmful toxins present in eucalyptus leaves.²²

A vaccine to protect koalas against chlamydia has been developed and is currently being tested in clinical trials in Queensland, Australia. The vaccine contains small fragments of the Chlamydia pecorum bacterium, which trains the immune system of inoculated koalas to recognise and combat the pathogen when they are exposed to it. So far, the results of the clinical trials are positive, showing that the vaccine successfully prevents koalas from getting ill if they catch chlamydia. It can also reduce the severity of symptoms severity in infected koalas. For example, a recent study in 2024 reported results from a decade of clinical trials.²³ During that period, 680 koalas were tracked, with five vaccine trials involving 165 koalas. Results showed that vaccinated koalas were 64% less likely to die from chlamydia and had significantly lower disease incidence.

Unfortunately, the number of koalas left in the wild is dwindling. In the early 1900s there were millions of koalas in Australia, but currently the International Union for the Conservation of Nature (IUCN) estimates that there are only 100,000 to 500,000 koalas left in the wild.²⁴ However, some groups say that as few as 50,000 koalas remain and the species is officially listed as endangered along much of the east coast.²⁵ Some claim that koalas could become extinct in some states within a generation.

As well as the diseases like chlamydia, koalas face existential threats from deforestation and habitat loss. Land clearing, logging and bushfires have already destroyed much of the forest that koalas live in. As the planet warms, more intense and frequent droughts and bushfires are expected, which poses an increasing threat to koalas. For example, the unprecedented 2019-20 Australian bushfire season killed or displaced nearly three billion animals, including koalas.²⁶ The problem is exacerbated by the fact that koalas need a lot of space to live in – about 100 trees per animal, reportedly.²⁷ Destruction of their woodland habitat also means koalas must travel longer distances to find trees, which is not only energetically costly given their diet, but also increases the probability of encountering risks, such as vehicle collisions and dog attacks.²⁸

Koalas are listed as vulnerable by the IUCN, with koalas listed as one of 10 animals most vulnerable to climate change.²⁹ To make matters worse, increasing levels of carbon dioxide in the atmosphere is expected to reduce the nutritional quality of eucalyptus leaves.³⁰ That, coupled with more frequent droughts, means that koalas will have to spend less time sleeping, and more time eating and looking for sources of water.³¹ This will force koalas to exert more energy and put them at a higher risk of predation. 

The Australian government has listed the koala as one of 113 animals requiring urgent help.³² In response, wildlife hospitals, rescue organisations, and zoos have increased their efforts to care for injured koalas with the goal of eventually releasing them back into the wild.

Koalas are certainly cute and cuddly – their fur is thick and soft, and they have beautiful fluffy white ears. So it’s no wonder that, for visiting celebrities, royals, tourists and locals alike, no visit to Australia seems to be complete without a hug from a cuddly koala bear. However, despite their cuddly façade, koalas have sharp teeth and very sharp long claws that they use for climbing and holding on to trees. Nevertheless, koalas will rarely attack humans. They are solitary animals that keep to themselves, eating and sleeping most of the day. They will only become aggressive if they feel stressed or cornered, for example if they are picked up.

In fact, it is illegal to hold and cuddle koalas in all Australian states that host wild koala populations, except for Queensland and South Australia. Although the practice is still legal in Queensland, several zoos and wildlife parks are beginning to outlaw hugging koalas. For example, in July 2024, the world’s oldest koala sanctuary – Lone Pine, in Brisbane, Queensland – announced it would no longer offer visitors a chance to hold koalas.³³ International animal welfare organisations have also called for koala cuddling to be officially outlawed.³⁴ Although koalas could harm humans if cornered, the main reason behind banning the hugging of koalas is to protect these wild animals from harm. Studies have shown that interacting with, and cuddling humans stresses koalas out, preventing them from spending time sleeping and eating.³⁵

Koalas have quite a diverse vocal repertoire, with male, female and baby koalas making different calls. Baby koalas yip and squeak to attract the attention of their mother. Male koalas, on the other hand, are renowned for their noisy displays, which they use to attract females and announce their territory. The male koala starts by making a series of snore-like snorts, before moving on to grunts, growling and belching sounds. He then bellows and roars extremely loudly to announce himself to any neighbouring females. Interestingly, the noise a male koala makes is about 20 times lower than you would expect given his size.³⁶ This is due to an extra pair of vocal folds located outside the larynx between the koala’s oral and nasal cavities. The larger the male, the lower his voice and the further the sound travels. Female koalas can also make grunting and bellowing noises, but they tend to be much quieter. They sometimes make screeching and crying noises if they are distressed or threatened, particularly by the unwelcome advances of a nearby male.³⁷

In a 2019 study, researchers at the University of Sydney observed a group of wild koalas over two weeks during the hottest time of the year.³⁸ They found that on the mornings of what would turn out to be the hottest days, koalas lowered their body temperatures. This suggests that koalas predict the hottest days from morning conditions and adjust their core temperatures accordingly.

Normally, koalas maintain a core body temperature of around 36.3 degrees. However, on the morning of the hottest day of the study, where temperatures reached a high of 40.8C, the lowest ever recorded temperature for a koala was measured (32.4C). This ability to lower their core body temperature is likely an adaptation that helps koalas reduce water loss on very hot days. This is because, by starting at a cooler body temperature, koalas can allow their body heat to rise with air temperature rather than attempting to keep their temperature strictly within the normal range – a process that would result in water loss through evaporative cooling.

Featured image © David Clode | Unsplash

Fun fact image © Pascal Mauerhofer | Unsplash

Quick Facts:

1. Source: Top 10 Facts about Koalas. World Wildlife Fund.  https://www.wwf.org.uk/learn/fascinating-facts/koala

Fact file:

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