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Chimps Use Insects to Soothe Each Other's
Wounds in Never-Before-Seen Behavior
CARLY CASSELLA
7 FEBRUARY 2022
In 2019, Alessandra Mascaro, a volunteer and budding evolutionary biologist
for
The Loango Chimpanzee Project
, noticed something no other
primatologist in Africa had reported before.
In the forests of Gabon, while following and filming a female chimpanzee
Suzee and her son Sia, Mascaro noticed Suzee clamp something tiny
between her lips, before applying the invisible matter to a wound on Sia's
foot.
Looking back at her footage, Mascaro realized Suzee had snatched the
topical treatment straight from the underside of a leaf. It looked like a tiny,
dark insect.
"Discussing these observations and the possible function of the behavior
with the team members, we realized that we had never seen such a behavior
and that it had also never been documented before,"
says
Mascaro.
Once aware of the practice, Mascaro and her colleagues began to notice it
regularly.
A week after Mascaro's sighting, Lara Southern, a PhD student on the
research team, watched as an adult male chimpanzee pulled a leaf towards
his mouth, picked up an insect with his lips, and grabbed the creature with
his thumb and forefinger. The chimp then applied what he'd snatched from
the shrub to a day-old wound in the crook of his arm.
Over the next 15 months, researchers for the chimpanzee project carefully
documented 20 other similar events on the west coast of Africa. Most of the
time, the chimpanzees in Gabon applied the unidentified insects to their own
wounds, but there were several occasions in which they also helped each
other out.
"An adult male, Littlegrey, had a deep open wound on his shin and Carol, an
adult female, who had been grooming him, suddenly reached out to catch an
insect,"
recalls
Southern.
"What struck me most was that she handed it to Littlegrey, he applied it to
his wound and subsequently Carol and two other adult chimpanzees also
touched the wound and moved the insect on it. The three unrelated
chimpanzees seemed to perform these behaviors solely for the benefit of
their group member."
Prosocial behaviors that promote empathy amongst a group of animals are
controversial in evolutionary biology, as they seem to undermine the basic
'selfishness' of survival.
Self-medication is
quite common in the animal kingdom
, seen in birds, bees,
lizards, elephants, and chimpanzees, but selfless behaviors with regards to
medicine are exceedingly rare.
While chimpanzees and bonobos have been observed swallowing the leaves
of medicinal plants to help ward off intestinal infections, the topical
application of insects as medicine is a new discovery.
"Our observations provide the first evidence that chimpanzees regularly
capture insects and apply them onto open wounds,"
says
primatologist
Tobias Deschner from the University of Massachusetts.
"We now aim to investigate the potential beneficial consequences of such a
surprising behavior."
The insects used by the chimpanzees for this topical treatment have yet to
be identified, but judging by how quickly the primates must move to snatch
the dark-colored arthropods from their surroundings, the authors suspect
they are probably winged and hold some sort of anti-inflammatory or
antiseptic properties.
Humans themselves are known to use insects in a very similar way, as the
small bodies of some invertebrates
hold medicinal properties
. Written
records, for instance, indicate that '
maggot therapy
' has been used by
humans to treat wounds for thousands of years all over the world.
Despite decades-worth of chimpanzee observations in Africa, however, this
is the first time we've noticed a similar behavior among our closest living
relatives, and it suggests our species isn't the only one to play the roles of
doctor and patient.
Chimpanzees are known to display several behaviors that
appear to be
prosocial on the surface
, including food sharing, adoption, territorial patrols
and cooperative hunting, but the meaning and purposes of these acts are
debated among evolutionary biologists. Some other studies suggest chimps
are only concerned with their own wellbeing.
The topical application of medicine to another chimp's wounds strengthens
the idea that humans aren't the only ones who can act in the interests of
another. Studying chimps further could help us understand how such
prosocial behaviors first began to evolve and what their evolutionary
benefits might be.
"It is just fascinating to see that after decades of research on wild
chimpanzees they still surprise us with unexpected new
behaviors,"
says
Deschner.
"Our study shows that there is still a lot to explore and discover about our
closest living relatives, and we therefore need to still put much more effort
into protecting them in their natural habitat."
The study was published in
Current Biology
.
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