Chimps observed medicating themselves - and others - with insects for the first time

Published Feb 8, 2022

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Gabon - At the Loango National Park in the Central African country of Gabon, adult chimpanzee Suzee is shown inspecting a day-old wound on the foot of her adolescent son, Sia.

Then, she abruptly sits up, grabs an insect from a nearby branch and pops it in her mouth. She takes Sia's foot and applies the insect to the wound, repeating the process of extraction and application twice over as her daughter looks on.

It was a moment, captured on video in 2019, that a group of researchers say marks the first time such behavior was observed and studied in chimpanzees. The incident prompted the Ozouga Chimpanzee Project to begin further monitoring. Now they say that over the course of 15 months, their researchers have observed 19 instances of chimpanzees applying insects to wounds on themselves - and three times to the wounds of others.

In correspondence published in Current Biology Monday, the researchers said that they were reporting the first observations of chimpanzees self-medicating with insects. They argued that the behavior is further evidence that chimpanzees have the capacity for "prosocial behaviors," or voluntary actions that serve the best interest of another.

Those behaviors are linked to empathy in humans and, the researchers note, have "long posed a problem for evolutionary theory, because it was not immediately clear why organisms might help others in the face of selection operating in the interest of self."

But chimpanzees have become important candidates for the study of prosocial behaviors because they exhibited cooperation in territorial patrols and coalitionary aggression, the researchers wrote.

Other animals have been known to self-medicate, consuming non-nutritional plants that are not part of their regular diet to soothe pain or cure an infection. Bears and deer consume medicinal plants; pregnant elephants in Kenya eat specific leaves to induce delivery; and some chimpanzees swallow rough leaves to rid their intestines of parasites, according to a Proceedings of the National Academy of Sciences of the United States of America article.

"In the video, you can see that Suzee is first looking at the foot of her son, and then it's as if she is thinking, 'What could I do?' and then she looks up, sees the insect and catches it for her son,'" said Alessandra Mascaro, a volunteer at the Ozouga Chimpanzee Project, who first observed the behavior.

The researchers have not yet identified the exact insect being used as a remedy, but have theorized that they may have "soothing properties" for pain relief.

The chimpanzees work in the same sequence: First, they catch an insect; second, they immobilize it by squeezing it between their lips; third, they place the insect on the wound and move it around; and finally, they remove the insect from the wound with their mouth or fingers.

"Studying great apes in their natural environments is crucial to shed light on our own cognitive evolution," said Tobias Deschner, a primatologist with the project, in a news release. "We need to still put much more effort into studying and protecting them and also protecting their natural habitats."

WASHINGTON POST

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