- For the first time, researchers observed chimpanzees applying insects to their own wounds and the wounds of others.
- Although questions remain, the topical application of these insects appears to be an instance of self-medication.
- Treating others’ wounds with insects may demonstrate prosocial behavior, which is rarely observed in species other than humans.
Researchers with the Ozouga Chimpanzee Project have been studying a group of about 45 chimpanzees in Loango National Park in Gabon for seven years. But in late 2019, Alessandra Mascaro, then a volunteer with the project, observed something none of them had seen before.
She was filming a female named Suzee interacting with her adolescent son, Sia. As Mascaro watched, Suzee appeared to grab something out of the air, put it between her lips, and then apply it to an open wound on Sia’s foot. Mascaro shared her unusual observation with a colleague at the project, Ph.D. student Lara Southern. A week later, Mascaro and Southern observed two more instances of similar behavior among the chimpanzees.
Mascaro showed the footage to her supervisors, Tobias Deschner, a primatologist with the project, and Simone Pika, a cognitive biologist at Osnabrück University. The team worked out that the tiny objects grabbed from the air were most likely some sort of flying insect. But they all agreed that such a behavior had never been documented before.
During the following year, the researchers began to look out for and film all individuals with injuries. They collected 22 observations of chimpanzees applying insects to either their own wounds or the wounds of others. Given that the behavior was only observed in association with open wounds, the researchers suggest that the applied insects may have anti-inflammatory or antiseptic properties. The team reported their findings in the journal Current Biology.
A Helping Hand
Self-medication, where individuals use parts of plants or non-nutritional substances to combat pathogens or parasites, has been observed across many animal species, including insects, reptiles, birds, and mammals. Chimpanzees, for instance, are known to swallow or chew plant leaves with antiparasitic properties to kill intestinal parasites.
“The topic of self-medication in chimpanzees is not new,” says Southern. “What has never been observed before is any kind of topical application of a substance to skin wounds.”
Another remarkable aspect of the team’s observations is that the chimpanzees not only treated their own wounds but also applied the insects to the wounds of other, sometimes non-related, individuals.
“It is interesting because when we saw chimpanzees applying insects onto others, the wound was easily reachable by the injured chimpanzee,” says Mascaro. “In those cases, the injured animal did not need the help, yet the other animal still gave it.”
The researchers argue that this is an example of prosocial behavior—behavior that acts in the best interests of others, rather than just oneself. In humans, such behaviors seem to be driven by empathic concern for others. Whether other species also demonstrate prosocial behaviors is an area of debate among scientists.
Southern says that the relationship between the individuals involved is important. Mascaro’s first observation involved two related individuals, a mother and son. But the team also observed two instances where completely unrelated chimpanzees took part in the behavior.
“In chimpanzee society, bonds between adult males and adult females tend to be the weakest,” says Southern. “Male-male bonds are quite strong, as are female-female and female-offspring bonds.
“But we recorded interactions between an adult male and an adult female who wouldn’t be considered to share an especially close relationship.”
The discovery of this surprising behavior has opened up a flood of new questions for the research team. Among their next steps is investigating the potential benefits of topical insect application, such as the efficacy of the treatment in helping wounds heal.
The team is also keen to identify the insect species used by the chimpanzees. Identification is challenging, as the chimpanzees mash the insects as part of their process. But Mascaro and her colleagues hope to recover remaining insect parts on which they can carry out bioassays to learn more.
“We don’t know if it’s just one species or more than one,” says Mascaro. “With analyses of these insects, maybe we can discover new substances with potential medicinal properties.”
In addition, the team will focus on elucidating the social dimensions of the behavior, such as which individuals tend to give the treatment and which tend to be on the receiving end, as well as the acquisition and transmission of the behavior in the community.
The research team says their observations show that, even after decades of field studies on wild chimpanzees, there is still much to explore and discover about these apes.
“This study is the starting point of figuring out why and how often this behavior happens and if it occurs in other populations,” says Southern. “What’s come to light from years of research is the fact that we’re still scratching the surface of what we know about chimpanzee populations and cultures.”
Mascaro, A., Southern, L. M., Deschner, T., and Pika, S. (2022). Application of insects to wounds of self and others by chimpanzees in the wild. Current Biology 7 February 2022. DOI: 10.1016/j.cub.2021.12.045.