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Do koalas smell like cough drops?

Koalas spend most of their time taking it easy. See more pictures of marsupials.
Jeff Foott/Discovery Channel Images/Getty Images

In the eucalyptus forests of Australia, you'll find the world's remaining wild koalas eating leaves and sleeping. That's pretty much all these marsupials do. They sleep for up to 20 hours a day cradled in eucalyptus branches, wake up to eat some leaves and go back to snoozing on a full stomach. It's a lazy life that revolves around a monotonous diet, and koalas are perfectly adapted to it.

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Eucalyptus leaves have very little nutritional value, provide almost no energy (in the form of calories), are hard to digest and are poisonous to almost every mammal besides the koala (Phascolarctos cinereus). Needless to say, koalas face little competition for their favorite food source. They consume up to 1.5 pounds (680 grams) of leaves in a single day -- that's about 1,000 leaves [sources: San Diego Zoo, Globio]. They spend pretty much all of the energy they get from the leaves on chewing and digesting them. Eucalyptus leaves are so fibrous that most animals wouldn't go near them even if they were safe to eat.

 

How can koalas eat eucalyptus? Koalas have cheek teeth that grind up the tough leaves, and their other teeth are spaced specifically to slice the leaves into smaller pieces they can swallow. But the most important part happens inside, when a eucalyptus-friendly digestive system takes over.

 

A koala's digestive tract is full of different types of bacteria that make eucalyptus both safe and (somewhat) digestible. A koala has an organ called a caecum (humans actually have it, too, but a koala's is much bigger). The caecum contains bacteria that break down the eucalyptus fibers. This makes it so at least some of the leaf (about 25 percent) can be digested -- converted into calories for nutrition and energy [source: AKF]. The other digestive trick is a bacterium that neutralizes the toxins in eucalyptus oil, mostly cineole, the poisonous component that makes the leaves unsafe for most mammals.

 

Of the roughly 500 types of eucalyptus trees out there, koalas only go for a couple of dozen types. And of those, a particular group of koalas will have a few favorites. Eating the same few types of eucalyptus all of the time probably helps koalas learn the scent of a leaf that has a different toxic substance in it called prussic acid. Prussic acid is toxic even to koalas, so they have to be very careful not to eat those leaves.

Koalas are all about eucalyptus, and eucalyptus is an ingredient in many a cold remedy. But how can a cold remedy contain a poison? On the next page, we'll learn what makes eucalyptus medicinal -- and find out if koalas really smell like cough drops.

When koalas aren't eating eucalyptus leaves, they're probably napping.
When koalas aren't eating eucalyptus leaves, they're probably napping.
Tim Graham/The Image Bank/Getty Images

It's not hard to see why a koala might smell like eucalyptus. It's pretty much all they eat. This means koalas hardly ever have to leave the trees, so they're out of reach from the countless predators who would find the little 25-pound (about 11 kg), slow-moving marsupial an easy target. It also means they can sometimes smell like cough drops.

Only sometimes, though -- it's mostly the young koalas that give off a slight eucalyptus scent. Adult koalas smell more like a mixture of urine and koala-mating musk, according to the Australian Koala Foundation.

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And here we come to an interesting question: If eucalyptus oil is toxic, how can it be used in cough drops? As with most substances, it's all about moderation. What's toxic at high doses can be beneficial in small amounts. Koalas eat lots of different types of eucalyptus leaves, some of which contain tremendous amounts of toxins like cineole. Oil from eucalyptus leaves can be up to 95 percent cineole. Most herbal remedies containing eucalyptus, which date back at least hundreds of years in the Aboriginal tribes of Australia, come from the species E. globulusis, or blue gum. The oil in blue gum leaves contains much less cineole, as little as 4 percent by volume [source: Cornell].

Eucalyptus oil finds its way into cough drops mostly because of its anti-inflammatory properties, which are attributed to the cineole. But it doesn't stop there: Eucalyptus is something of an "alternative medicine" cure-all. It's an antiseptic and a sedative, and it has both antimicrobial (kills viruses) and antibacterial properties. It's used in herbal medicine to treat everything from the common cold to fungal infections to bronchitis. It may even help with ear infections [source: UMMC].

With all of eucalyptus oil's medicinal applications, you'd think koalas would be protected against just about every nuisance out there. But no, they're still subject to their own health concerns. Eucalyptus oils may protect eucalyptus trees from bugs and parasites, but koalas have as many ticks as the next marsupial. They also have the sexually transmitted disease chlamydia in strangely large numbers [source: Science Daily]. Aside from that, though, the biggest threats to koalas are domestic dogs, speeding cars and, of course, greenhouse gasses: An increase in carbon dioxide may be sapping what few nutrients eucalyptus leaves have to offer.

For more information on koalas, eucalyptus and related topics, look through the links on the next page.

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Related HowStuffWorks Articles

More Great Links

 

 

Sources

 

  • Australian Koala Foundation. https://www.savethekoala.com/koalasdiet.html
  • Eucalyptus. University of Maryland Medical Center. http://www.umm.edu/altmed/articles/eucalyptus-000241.htm
  • Eucalyptus spp. Treating Livestock with Medicinal Plants: Beneficial or Toxic? Animal Science. Cornell University. http://www.ansci.cornell.edu/plants/medicinal/eucalyp.html
  • A home among the gum trees. Zoo Friends. ZooNooz June 2002. http://www.zoofriends.org.au/zoonooz/zoonooz_june02_article2.html
  • Koala. Enchanted Learning. http://www.enchantedlearning.com/subjects/mammals/marsupial/Koalaprintout.shtml
  • Koala. HowStuffWorks. https://animals.howstuffworks.com/mammals/koala-info.htm
  • Koala. Kids' Planet. http://www.kidsplanet.org/factsheets/koala.html
  • Koala. Park Victoria. http://www.parkweb.vic.gov.au/education/factfiles/03.htm
  • Koala. San Diego Zoo. http://www.sandiegozoo.org/animalbytes/t-koala.html
  • Koalas. Globio.org. http://www.globio.org/glossopedia/article.aspx?art_id=62
  • Koalas under threat from toxic eucalyptus leaves. May 7, 2008. CNN.com. http://www.cnn.com/2008/TECH/science/05/07/koala.threat.ap/index.html

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