Animals self-medicate with the behavior of plants that humans have observed and imitated for millennia

When a wild orangutan in Sumatra recently suffered a facial wound, apparently after a fight with another male, it did something that caught the attention of the scientists observing it.

The animal chewed the leaves of a liana vine, a plant not normally eaten by monkeys. Over several days, the orangutan carefully applied the liquid to his wound, then covered it with a chewed liana paste. The wound healed with only a faint scar. The tropical plant he chose has antibacterial and antioxidant properties and is known to relieve pain, fever, bleeding and inflammation.

The surprising story was picked up by the media around the world. In interviews and in their research paper, the scientists stated that this is the first systematically documented case of active wound treatment by a wild animal with a biologically active plant. The discovery will provide new insights into the origins of human wound care.

left: four leaves next to a ruler.  right: an orangutan in a treetop
Fibraurea tinctoria the leaves and the orangutan rubbing some of the leaves.
Laumer et al, Sci Rep 14, 8932 (2024), CC BY

The orangutan’s behavior seemed familiar to me. As a historian of ancient science investigating what the Greeks and Romans knew about plants and animals, I was reminded of similar cases reported by Aristotle, Pliny the Elder, Aelian, and other naturalists from antiquity. A remarkable number of stories from ancient times to the Middle Ages describe self-healing by many different animals. Animals used plants to treat disease, repel parasites, neutralize poisons, and heal wounds.

The term zoopharmacognosy was coined in 1987. But as the Roman natural historian Pliny pointed out 2,000 years ago, many animals have made medical discoveries useful to humans. Indeed, a large number of medicinal plants used in modern medicine were first discovered by indigenous peoples and past cultures, who observed animals using plants and imitated them.

What you can learn by watching animals

Some of the earliest written examples of animal self-medication appear in Aristotle’s History of Animals from the fourth century BC, such as the well-known habit of dogs to eat grass when they are sick, possibly for cleansing and deworming.

Aristotle also noted that after hibernating, bears look for wild garlic as their first food. It is rich in vitamin C, iron and magnesium, healthy nutrients after a long winter sleep. The Latin name reflects this popular belief: Allium ursinum translates to bear lily, and the common name in many other languages ​​refers to bears.

medieval image of a deer wounded by a hunter's arrow, while a fallow deer is also wounded but eats the grass of the day, causing the arrow to come out
As a hunter shoots a few arrows into his quarry, a wounded doe ingests a growing dina.
British Library, Harley MS 4751 (Harley Bestiary), folio 14v, CC BY

Pliny explained how the use of ditan, also known as wild oregano, to treat arrow wounds arose from the sight of wounded deer grazing on the grass. Aristotle and Dioscorides credited wild goats with the discovery. Vergil, Cicero, Plutarch, Solinus, Celsus, and Galen asserted that ditaku has the ability to expel an arrowhead and close a wound. Among ditans, many known phytochemical properties are antiseptic, anti-inflammatory and coagulant effects.

According to Pliny, the deer also knew an antidote for toxic plants: wild artichokes. The leaves relieve nausea and stomach cramps and protect the liver. To cure themselves of spider bites, Pliny wrote, deer ate crabs washed up on the beach, and sick goats did the same. In particular, crab shells contain chitosan, which boosts the immune system.

When elephants accidentally ingested chameleons hidden in green foliage, they ate olive leaves, a natural antibiotic to fight salmonella harbored by the lizards. Pliny said that ravens eat chameleons, but then eat bay leaves to combat the lizards’ toxicity. Antibacterial bay leaves relieve diarrhea and gastrointestinal upset. Pliny noted that blackbirds, partridges, laurels and pigeons also eat bay leaves for digestive problems.

17th century engraving of a weasel and a basilisk in conflict
A weasel wields a girdle as it attacks a basilisk in an illustration from a 1600s bestiary.
Wenceslaus Hollar/Wikimedia Commons, CC BY

Weasels were said to roll in the path of the evergreen plant to ward off wounds and snakebites. Fresh rue is toxic. Its medicinal value is unclear, but the dried plant is included in many traditional folk remedies. Swallows collect another toxic plant, celandine, to make a poultice for the eyes of their birds. Snakes coming out of hibernation rub their eyes on the fennel. Fennel bulbs contain compounds that promote tissue repair and immunity.

According to the naturalist Aelian, who lived in the third century BCE, the Egyptians traced much of their medical knowledge to the wisdom of animals. Aelian described elephants treating spear wounds with olive blossoms and oil. He also mentioned storks, partridges and pigeons crushing oregano leaves and applying the paste to wounds.

The study of animal medicines continued into the Middle Ages. An example from the 12th-century English compendium of animal lore, the Aberdeen Bestiary, tells of bears covering wounds with scabs. Folk medicine prescribes this flowering plant to soothe pain and heal burns and wounds, thanks to its anti-inflammatory chemicals.

Ibn al-Durayhim’s 14th-century manuscript The Usefulness of Animals reported that swallows cured nestlings’ eyes with turmeric, another anti-inflammatory. He also noted that wild goats chew and apply sphagnum moss to wounds, just as the Sumatran orangutan did with liana. Sphagnum moss dressings neutralize bacteria and fight infection.

Nature’s Pharmacopoeia

Of course, these premodern observations were folk knowledge, not formal science. But the stories reveal the long-term observation and imitation of various animal species self-medicating with bioactive plants. Just as traditional indigenous ethnobotany is leading to life-saving medicines today, scientific testing of ancient and medieval claims can lead to discoveries of new therapeutic plants.

Animal self-medication has become a rapidly growing scientific discipline. Observers report sightings of animals, from birds and rats to pigs and chimpanzees, deliberately using an impressive repertoire of medicinal substances. A surprising observation is that finches and sparrows collect cigarette butts. Nicotine kills mites in bird nests. Some veterinarians even allow sick dogs, horses, and other pets to choose their own prescriptions by sniffing different botanical compounds.

Mysteries remain. No one knows how animals know which plants cure disease, heal wounds, ward off parasites, or otherwise promote health. Do they deliberately react to particular health crises? And how is their knowledge transmitted? What we do know is that we humans have learned the secrets of healing by watching animals heal themselves for millennia.

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