Scientists observed a wild male orangutan repeatedly rubbing chewed leaves of a medicinal plant on a facial wound in a forest reserve in Indonesia.
It was the first known observation of a wild animal using a plant to heal a wound, and adds evidence that humans are not alone in using plants for medicinal purposes.
The male orangutan, Rakus, lives in Gunung Leuser National Park on the island of Sumatra and is believed to be around 35 years old. For years, researchers have followed orangutans like him on his travels through the forest, picking his way through the canopy in search of fruit to eat.
Scientists at the park's Suaq Balimbing research area first noticed a wound on his face on June 25, 2022, when they saw his self-medicating behavior begin.
“When I heard about it, I was very excited,” said Isabelle Laumer, a primatologist at the Max Planck Institute for Animal Behavior in Germany, partly because records of animals grooming themselves are rare, especially when it comes to to heal wounds. . She and her colleagues detailed the finding in a study published Thursday in the journal Scientific Reports.
The plant used by Rakus, known as akar kuning or yellow root, is also used by people throughout Southeast Asia to treat malaria, diabetes and other conditions. Research shows that it has anti-inflammatory and antibacterial properties.
Orangutans rarely eat the plant. But in this case Rakus ingested a small amount and also covered the wound several times. Five days after the wound was noticed, it had closed and less than a month later “it healed with no sign of infection,” Dr. Laumer said.
Michael Huffman, a visiting professor at the Institute of Tropical Medicine at Nagasaki University in Japan, who was not involved in the study, said: “This is, as far as I know, the first published study to demonstrate that an animal uses a plant with known biomedical properties for the treatment of a wound.”
It has been observed that in the past primates appeared to heal wounds, but not with plants. A group of more than two dozen chimpanzees in Gabon, central Africa, were seen chewing and applying flying insects to their wounds, said Simone Pika, an animal cognition expert at the University of Osnabrück in Germany, who documented observation.
Orangutans have been spotted using medicinal plants in a different way: In 2017, scientists reported that six Bornean orangutans rubbed the chewed leaves of a shrub with anti-inflammatory and analgesic properties on their legs and arms, probably to soothe aching muscles .
“The overall patterns of application are similar, which is good for our understanding of the species' propensity for this type of pharmacological behavior,” Dr. Huffman said.
Examples of self-medication in primates remain rare and the behavior is not fully understood. Chimpanzees, bonobos, gorillas, and white-handed gibbons are known to occasionally eat whole, rough leaves, presumably to help them expel parasites. Dr. Huffman and others have also seen chimpanzees chew the bitter pith of a plant called Vernonia amygdalina to treat worm infections.
But this behavior is not exclusive to primates. Indian civets, a cat-like mammal, also swallow leaves whole, most likely to get rid of worms. Various birds engage in a strange behavior, called antism, in which they rub on ants, to help them cure feather mites or other parasites. Hundreds of bee species also collect flower extracts that prevent the growth of fungi and bacteria in their colonies, which could be considered a kind of preventative or group self-medication.
Dr. Laumer hopes Rakus' study will help create greater appreciation for – and desire to protect – the Sumatran orangutan, a critically endangered species. Even after 30 years of studying in the park, researchers are learning new things.
Just in the last few years, scientists have shown that orangutans can solve complex puzzles, engage in planning for the future, playfully tease each other and laugh, like humans.
“There are so many things we still don't know about these monkeys,” he said.