“Every Species On The Planet Self-Medicates In Some Way”: How Wild Animals Use Medicine

Of course, no monkey is making for the medical center, nor are lions sipping Lemsip or alpacas popping Advil, but a rudimentary form of medicine may be common – ubiquitous even, some argue – in the animal kingdom.

Do animals use medicine?

“Every species on the planet self-medicates in some way or another,” Michael Huffman, a primatologist now at the Institute of Tropical Medicine at Nagasaki University, told IFLScience, highlighting the myriad examples of the practice in primates and other mammals, as well as bird species.

Often referred to as zoopharmacognosy, this self-medication in animals tends to involve plants or other non-nutritional substances – such as soils and insects – being ingested or applied topically to combat disease. Think of the natural world as a fully stocked medicine cabinet at any animal’s disposal.

Self-medication, or at least what appears to be self-medication, has been observed in the animal kingdom – particularly among the great apes – for decades. However, there was some initial skepticism as to whether these species were truly medicating themselves and if so, whether it was effective. After all, a chimp swallowing a leaf could be doing it just because, and not in some ingenious attempt to treat a parasite.

In the years since, research has started to accrue in favor of self-medication in animals – and Huffman has played a big part in that. His work with chimpanzees in Africa, for example, revealed instances of wild chimps consuming the plant Vernonia amygdalina (bitter leaf) seemingly to treat parasite-related diseases.

“There is widespread evidence of such behaviors as whole leaf swallowing, bitter pith chewing, and fur rubbing in African great apes, orangutans, white handed gibbons, and several other species of monkeys in Africa, Central and South America, and Madagascar,” Dr Isabelle Laumer, from the Max Planck Institute of Animal Behavior, told IFLScience. Topical application of medicinal compounds, on the other hand, is rarely witnessed – though recent research has changed that. 

In a 2022 study, chimpanzees were reported applying insects to their wounds, and occasionally those of other members of their troop, for the first time. We don’t yet know how effective this seeming self-medication is, Laumer explained: “Further research is needed to investigate the efficiency of this behavior.”

Woolly bear caterpillars – thought to be the first recorded self-medicating insect – are believed to deliberately eat poisonous plants to rid themselves of parasites.

Then, last year, Laumer was first author of a study detailing the case of Rakus the Sumatran orangutan, who was caught chewing the leaves of the Akar Kuning plant (Fibraurea tinctoria) – used in traditional medicine to treat dysentery, diabetes, and malaria – before applying the juice to a facial wound, which healed without infection. The behavior was repeated several times, and later the wound was covered with solid plant material. It was the first documented case of active wound treatment using a biologically active plant by a wild animal.

Examples of what may be self-medication also exist outside of primates. There is evidence to suggest that goats may self-medicate using plants with anthelmintic properties to counter gastrointestinal worms. Meanwhile, parrots, and other animals, eat clay, possibly to neutralize toxins in their diet.

Even creepy crawlies get involved: Some ants use a mixture of tree resin and formic acid in an antimicrobial cocktail (there’s a pun to be made there, but we’ll spare you) to protect their colonies from disease. And woolly bear caterpillars – thought to be the first recorded self-medicating insect – are believed to deliberately eat poisonous plants to rid themselves of parasites or to boost their own immune systems.

These examples are just the tip of the iceberg of animal self-medication – there’s plenty more where they came from. There’s even some evidence that non-human species are partial to recreational drug use, such as black-handed spider monkeys with a taste for boozy fruit.

From creature to clinician: How do animals acquire self-medication? 

All these animals are decidedly different – and not all of them famed for their intelligence. So how did they come by these self-medicating behaviors? Are they instinctual? Do they learn them? Is it our old friend natural selection at play again?

In the case of Rakus the orangutan, it could simply be a happy accident, Laumer told IFLScience. “Individuals may accidentally touch their wounds while feeding on Fibraurea tinctoria and thus unintentionally apply the plant’s juice to their wounds. As [the plant] has potent analgesic effects, Rakus may have felt an immediate pain release, causing him to repeat the behavior several times and subsequently apply solid plant matter.”

“But it may also be that Rakus has learned this behavior from other orangutans in his birth area,” Laumer added.

Learning could play an important part in propagating self-medication behaviors in some species, Huffman agrees.

“For all species, some aspect of self-medication is innate,” he told us. “But for social species that live in groups and are raised by their mothers, there are many aspects of the behavior that needs to be learned; what plants are used, what part [of] the plant, where are these plants in their habitat, etc.”

This may be the case for apes. Take chimps: We know them to be capable of learning and teaching, meaning it’s likely that knowledge of self-medication could be passed between generations. But for other animals, it might be a different story.

The existence of self-medication in our closest relatives could point to how such behaviors evolved in humans.

“You should never underestimate the power of natural selection,” Mark Hunter, a professor of ecology and environmental biology at the University of Michigan, told Joel Shurkin for a feature in PNAS. If eating a plant or putting its leaves on a scrape confers benefit to an animal, then those that happen to do it may be more likely to survive and pass on their genes – and possibly behaviors with them.

“It does not take a smart organism to develop an instinctive behavior,” Hunter added.

Nature’s pharmacy: What can we learn from animal “medicine”?

They might not have invented vaccines or mastered brain surgery, but there’s much we can learn from animals – even when it comes to medicine. If we look to them for clues about the medicinal properties of plants and other natural materials, our own drug cabinets could be all the richer for it. 

In a world with a growing antimicrobial resistance problem, coming by new medicines is imperative, and no mean feat. Could the silver bullet we’ve been searching for be lying in the hands of an orangutan or the belly of a caterpillar? It can’t hurt to look.

If we don’t learn about new medicines, we may at least be able to learn about ourselves. The existence of self-medication in our closest relatives could point to how such behaviors evolved in humans – who have been experimenting with wound healing since at least 2200 BCE.

“As forms of active wound treatment are not just a human universal but can also be found in both African and Asian great apes, it is possible that there exists a common underlying mechanism for the recognition and application of substances with medical or functional properties to wounds and that our last common ancestor already showed similar forms of ointment behavior,” Laumer added.

But perhaps, above all else, the knowledge that other animals often act as we do we should serve to deepen our understanding of and respect for the other species with which we share our planet. As Huffman put it: “Always we should learn to appreciate that animals, like humans, are capable of taking care [of] themselves, and we need to leave nature intact for the health of all animals and ourselves.”

This article first appeared in Issue 24 of our digital magazine CURIOUS. Subscribe and never miss an issue.