Loango National Park, GabonGabon’s Loango National Park recently provided the setting for researchers to observe a sight rare in nature: chimpanzees applying insects to their injuries.
The behavior – a unique demonstration of potentially advanced cultural activity – suggests the primate species may have long evolved health-related behaviors shared by members of closely related 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, savannas, coastal rainforests, floodplains and mangrove forests – that have created an explosion of biodiversity. The area is home to at least 80 mammal species, including 11 primate species, as well as leopard, forest elephant, hippo, swamp antelope and the elusive giant pangolin. The park is also home to 272 bird species.
Tobias Deschner, researcher at 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 collaboration with the Gabon National Park Authority (ANPN).
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Left: Thea, a man, immobilizes and lightly crushes an insect between his lips.
Right: Then he takes the insect out of his mouth and carefully places it on an open wound he sustained during a fight.
Photographs by Roland Hilgartner
The research team has been collecting behavioral data on the Rekambo community of about 40 primates for five years (Rekambo means “where English is spoken” in the local language). They filmed incredible scenes like chimpanzees attacking lowland gorillas and even killing and eating young ones. The team also observed the chimpanzees working together, using branches to dig up honey in underground beehives. (Read about a chimp who butchered its former leader.)
In February 2022, the scientists published their biggest discovery to date: chimpanzees deliberately treat their own wounds and those of their group with an unknown species of insect. It is the first time this behavior has been scientifically observed in great apes.
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, an area known as zoopharmacognosy. Decades ago, he observed wild, worm-infested chimpanzees swallowing the inner stem tissue of the African shrub Vernonia amygdalina. The plant contains antiparasitic agents and is also used by local people to treat intestinal pain.
When infested with roundworms, bonobos and gorillas ingest rough, hairy parts of plants that can fight parasites. At the same time, the bristly hairs of the plants increase intestinal activity and remove the worms. A few years ago, scientists also discovered that orangutans on Borneo were treating themselves with dragon tree extract.
Among great apes, grooming is a form of courtesy that signals affection. The same can apply to treating each other’s wounds.
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Mechanisms of self-medication are also known in 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, evolutionary biologist at Ozouga and leader of the February study, first noted in 2019 that the Rekambo chimps appeared to be healing their injuries. She watched a video clip of a 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 footage to Deschner and Pika, who were surprised by the scene. Subsequent videos showed that the behavior was not random or arbitrary, as other members of the Rekambo community also appeared to be treating injuries in the same way. In Mascaro’s study, she recorded 19 animals self-treating with insects.
Empathic Monkeys
Deep in the forest in Loango, Deschner observed Cesar, a chimp carrying coconut plums, being visited by two males. From about 20 feet away, he saw that one of the men had a large laceration on his left thigh and two open sores on his back. The second of the two men was also injured, bleeding from his wrist. (Read about other animals treating themselves, from birds to bees.)
Scientists have not yet identified the species of insect or the insects the chimpanzees harvest to treat their wounds.
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There appeared to have been a violent altercation the night before, probably caused by Pandi, the alpha male. After an absence of several days, Pandi rejoined the group, which may have increased tensions among the men.
The next morning I watched the chimpanzees groom each other’s fur. When the animals said goodbye, I followed Thea, one of the monkeys who had visited Cesar the day before and was still injured. From the look on his face, he was struggling with his injured leg – he was inspecting the wound with his fingers, his eyes scanning the surrounding vegetation as if searching for something.
Chimpanzees (pictured a male named Cesar) eat a wide variety of foods including fruits, nuts, seeds and insects. The approximately 60 square kilometer territory of the Rekambo chimpanzees includes almost all habitats of the national park, from the beach to the savannah to the rainforest.
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With a certain anticipation, I pulled my camera out of my backpack. Deschner also had his video camera ready. And then it happened.
Thea’s right hand reaches into the bushes like lightning. He catches an insect, maybe a fly, sitting on the underside of a leaf. He puts the animal in his mouth and lightly crushes 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 process a few more times before finally cleaning the wound with his fingers.
This pattern of behavior corresponds exactly to Mascaro’s first observation. And it’s all happening so quickly that it would be almost impossible to tell what was happening unless you observed it first.
Researcher Alessandra Mascaro observes Rekambo chimpanzees in the savannah.
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Three days later I observed another case of insect medication. This time it was another man who caught an insect and applied it to one of Thea’s wounds on his back. This behavior signaled to the scientists that chimpanzees also understand the well-being of others beyond mutual medication. It can be viewed as a prosocial behavior that scientists believe requires more complex cognitive skills. (Read how chimpanzees can have different personalities.)
After the two male chimpanzees move on, Mascaro searches the forest floor where they were. She – and all scientists – would like to know what kind of insect the chimpanzees used to analyze their chemistry. But the chimpanzees left no insects behind.
A stroke of luck
It’s hard to tell how aware some animals are of the connections between certain behaviors and pharmacological effects.
Furthermore, scientists can never be sure that behavior, even when intended, will produce a desired effect hours or even days later. Especially in the wild, there are often alternative explanations for why an animal is sick or gets well. Certain knowledge would require before and after investigations, which are often impossible with wild animals.
Fredy (left) nurses Thea, one of the men who is treating himself.
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The observations made by Mascaro and her colleagues on the Ozouga research team are unique because they documented the behavior firsthand, a fortunate observation, she says. Rekambo chimpanzees appear to only use the insect method when injured, limiting opportunities to see them in practice. (What wild chimpanzees can teach humans about healthy aging.)
Whether these findings have deep scientific meaning or are instead a mere behavioral fluke remains to be seen. Of course, humans are also known to do strange things – some proven, but many not – to achieve optimal health and well-being. Chimpanzees behaving the same way would be another commonality with our closest living relatives.
A version of this story was originally published in the September 2022 issue of the German edition of National Geographic magazine.
