Animals treat themselves with plants – a behavior humans have observed and imitated for millennia

When a wild orangutan in Sumatra recently suffered a wound to his face, presumably after a fight with another male, he did something that caught the attention of the scientists observing him.

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

The remarkable story was picked up by the media worldwide. 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

The orangutan’s behavior sounded familiar to me. As a historian of ancient science who studies 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 ancient naturalists. A remarkable collection of accounts from antiquity through the Middle Ages describes self-medication by many different animals. The animals used plants to treat disease, ward off parasites, neutralize toxins, and heal wounds.

The term zoopharmacognosy – “the knowledge of veterinary medicine” – was coined in 1987. But as the Roman natural historian Pliny noted 2,000 years ago, many animals have made medical discoveries that are useful to humans. Many medicinal plants used in modern medicine were first discovered by indigenous peoples and ancient cultures who observed animals using plants and mimicked them.

What You Can Learn From Observing Animals

Some of the earliest written examples of self-medication in animals appear in Aristotle’s History of Animals from the fourth century BCE, such as the famous habit of dogs to eat grass when they were sick, probably to purify and deworm themselves.

Aristotle also noted that bears seek wild garlic as their first food after hibernation. 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 means ‘bear lily’ and the common name in many other languages ​​refers to bears.

medieval depiction of a stag wounded by a hunter's arrow, while a doe is also wounded but eats the herb dill, causing the arrow to come outmedieval depiction of a stag wounded by a hunter's arrow, while a doe is also wounded but eats the herb dill, causing the arrow to come out

Pliny explained how the use of dittany, also known as wild oregano, to treat arrow wounds originated from watching wounded deer graze on the herb. Aristotle and Dioscorides attributed the discovery to wild goats. Virgil, Cicero, Plutarch, Solinus, Celsus, and Galen all claimed that dittany had the ability to expel an arrowhead and close the wound. Dittany’s many known phytochemical properties include antiseptic, anti-inflammatory, and coagulant effects.

According to Pliny, deer also knew an antidote to poisonous 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 that washed up on the beach, and sick goats did the same. Interestingly, crab shells contain chitosan, which strengthens the immune system.

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

17th century etching of a weasel and a basilisk in conflict17th century etching of a weasel and a basilisk in conflict

Weasels were said to roll in the evergreen rue to ward off wounds and snakebites. Fresh rue is poisonous. Its medicinal value is unclear, but the dried plant is used in many traditional folk medicines. Swallows gather another poisonous plant, celandine, to make a paste for the eyes of their chicks. Snakes emerging from hibernation rub their eyes in fennel. Fennel bulbs contain substances that promote tissue repair and immunity.

According to the naturalist Aelianus, who lived in the third century B.C., the Egyptians derived much of their medical knowledge from the wisdom of animals. Aelianus described elephants treating spear wounds with olive flowers and oil. He also mentioned storks, partridges, and turtledoves crushing oregano leaves and applying the paste to wounds.

The study of animal remedies continued into the Middle Ages. An example from the 12th-century English compendium of animal lore, the Aberdeen Bestiary, tells of bears covering sores with mullein. Folk medicine prescribed 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 healed the eyes of nestlings with turmeric, another anti-inflammatory. He also noted that wild goats chew and apply peat moss to wounds, much as the Sumatran orangutan did with lianas. Peat moss dressings neutralize bacteria and fight infection.

The pharmacopoeia of nature

Of course, these premodern observations were folklore, not formal science. But the stories reveal long-term observations and imitations of various species treating themselves with bioactive plants. Just as traditional indigenous ethnobotany leads to life-saving medicines today, scientific testing of the ancient and medieval claims could lead to discoveries of new therapeutic plants.

Self-medication in animals has become a rapidly growing scientific discipline. Observers report sightings of animals, from birds and rats to porcupines and chimpanzees, deliberately ingesting an impressive repertoire of medicinal substances. One surprising observation is that finches and sparrows collect cigarette butts. The nicotine kills mites in birds’ nests. Some veterinarians even let sick dogs, horses, and other pets choose their own medications by sniffing various botanical compounds.

Mysteries persist. No one knows how animals sense which plants cure illness, heal wounds, repel parasites, or otherwise promote health. Do they deliberately respond to specific health crises? And how is their knowledge passed on? What we do know is that for millennia, humans have learned healing secrets by watching animals medicate themselves.

This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Adrienne Mayor, Stanford University

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Adrienne Mayor does not work for, consult, own stock in, or receive funding from any company or organization that would benefit from this article, and she has disclosed no relevant affiliations beyond her academic appointment.

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