The behavior—a unique demonstration of potentially advanced cultural activity—suggests that the primate species may have developed longstanding health-related behaviors that are shared among members of tight-knit groups.
A large protected area on the west coast of Central Africa, Loango is a natural paradise: The area of more than 580 square miles contains a mosaic of different habitats—including rainforests, lagoons, wetlands, savanna, coastal rainforests, floodplains, and mangrove forests—that have created an explosion of biodiversity. The area is home to at least 80 species of mammals, including 11 species of primates, as well as leopards, forest elephants, hippos, swamp antelopes, and the shy giant pangolin. The park is also home to 272 bird species.
Tobias Deschner, a researcher with the University of Osnabrück in Germany, and his wife, Simone Pika, head of the research group for comparative cognitive biology at the Institute for Cognitive Sciences at the University of Osnabrück, lead the Ozouga Chimpanzee Project in cooperation with Gabon’s National Park Authority (ANPN).
The research team has been collecting behavioral data on the Rekambo community of about 40 primates (rekambo means “where English is spoken” in the local language) for five years. They have filmed incredible scenes, such as chimpanzees attacking lowland gorillas, even killing and eating young ones. The team also observed the chimps working together, using branches to dig out honey in underground beehives. (Read about a chimpanzee that cannibalized its former leader.)
In February 2022, the scientists published their biggest discovery yet: Chimpanzees deliberately treat their own wounds and those of their group using an unknown species of insect. It’s the first time the behavior has been scientifically observed in the great ape.
Self-soothing among other animals
Michael Huffman, a primatologist and professor at Kyoto University, is one of the pioneers of research into animal self-medication, a field known as zoopharmacognosy. He observed decades ago that wild worm-infested chimpanzees swallowed the inner stem tissue of the African shrub Vernonia amygdalina. The plant contains anti-parasitic agents and is also used by local people to treat intestinal pain.
When infested with roundworms, bonobos and gorillas swallow rough, hairy plant parts that can combat against parasites. At the same time, the bristly hairs of the plants increase intestinal activity and carry away the worms. Several years ago, scientists also discovered that orangutans in Borneo were treating themselves with dragon tree extract.
Mechanisms of self-medication are known even among non-primates. Some bird species “bathe” on anthills to rid themselves of ectoparasites, such as feather mites, with the help of formic acid. At least one pregnant elephant in Kenya has been observed eating certain plants that local naturopaths also use to induce labor in pregnant women.
Alessandra Mascaro, an evolutionary biologist with Ozouga and leader of the February study, first noticed in 2019 that the Rekambo chimpanzees seemed to treat their injuries. She watched a video clip of female chimpanzee applying a recently caught insect to an open wound on her son. A short time later the mother carefully removed the remains of the insect. The behavior looked like wound care.
Back in Germany, Mascaro showed the recordings to Deschner and Pika, who were surprised by the scene. Subsequent video showed that the behavior was not accidental or arbitrary, as other members of the Rekambo community appeared to also treat injuries in the same way. In Mascaro's study, she recorded 19 animals self-medicating with insects.
Deep in the forest in Loango, Deschner watched as Cesar, a chimpanzee carrying coconut plums, was visited by two males. From about 20 feet away, he saw one of the males had a large laceration on his left thigh and two open spots on his back. The second of the two males was also wounded, his wrist bleeding. (Read about other animals that self-medicate, from birds to bees.)
A violent altercation apparently broke out the night before, likely caused by Pandi, the alpha male. After an absence of several days, Pandi rejoined the group, which may have increased tension among the males.
The next morning, I observed the chimpanzees groom each other’s fur. When the animals parted, I followed Thea, one of the apes that visited Cesar the day before and was still injured. It seemed from his facial expressions that his injured leg was bothering him—he inspected the wound with his fingers, and his eyes scanned the surrounding vegetation, as if he were looking for something.
With a certain premonition, I pulled my camera out of my backpack. Deschner also had his video camera ready. And then it happened.
Like a flash, Thea’s right hand reaches into the bushes. He catches an insect, maybe a fly, sitting on the underside of a leaf. He puts the animal in his mouth, lightly crushing it with his lips. He then carefully applies the resulting mush to his flesh wound, stroking it back and forth with his fingertips. He repeats the procedure a few more times before finally cleaning the wound with his fingers.
This pattern of behavior corresponds exactly to Mascaro’s first observation. And the whole thing happens so quickly that, had it not been observed before, it’d be almost impossible to discern what’s happening.
Three days later, I observed another instance of insect medication. This time it was another male who caught an insect and applied it to one of Thea’s wounds on his back. This behavior signaled to the scientists that, even beyond medicating each other, chimpanzees understand the well-being of others. It may be considered prosocial behavior, which scientists believe requires more complex cognitive abilities. (Read how chimps can have different personalities.)
After the two male chimpanzees have moved on, Mascaro searches the forest floor where they were just a moment ago. She—and all the scientists—would love to know which insect species the chimpanzees were using in hopes of analyzing its chemistry. But the chimpanzees left no insects behind.
A lucky break
It hard to know how conscious some animals are about the links between certain behaviors and pharmacological effects.
What's more, scientists can never be certain whether a behavior, even if intentional, produced a desired effect hours or even days later. There are also often alternative explanations, particularly in the wild, for why an animal is sick or becomes well. Knowing for certain would require before-and-after examinations, which are often impossible with wild animals.
The observations of Mascaro and her colleagues with the Ozouga research team are unique because they documented the behavior firsthand, a lucky observation, she says. Rekambo chimpanzees only seem to use the insect method when injured, which limits the opportunities to see it in practice. (What wild chimps can teach people about healthy aging.)
Whether these findings hold deep scientific meaning or are instead a mere behavioral coincidence remains to be seen. Humans, of course, are also known to do strange things—some proven, but many not—to pursue optimal health and wellness. Chimpanzees behaving the same way would be another thing we have in common with our closest living relatives.
A version of this story was originally published in the September 2022 issue of National Geographic magazine’s German edition.