Medicinal Plant Use by Chimpanzees in the Wild
Because chimpanzees are so like us they are often used in laboratory
experiments to find cures for many human diseases. Chimpanzees are now also
teaching us about how they cure some of their own diseases in the wild.
Extensive field and laboratory studies in progress at Mahale Mountains
National Park show us how chimpanzees infected with nematodes use plants which
help keep their infections under control. It now appears that some of these
plants have a chemical effect (e.g. Vernonia amygdalina) while others
have a physical purging effect (e.g. Aspilia mossambicensis).
The strongyle nematode species Oesophagosotmum stephanostomum is largely
responsible for the observed cases of illness recorded at Mahale during the
rainy season, when these medicinal plants are most frequently used by
Bitter-pith chewing : Vernonia amygdalina
Chimpanzees carefully remove the leaves and outer bark from young shoots and
chew on the exposed pith, sucking out the extremely bitter juice. In a few
well-documented cases, chimpanzees have been shown to recover their appetites,
regain strength, lower parasite loads, and recover from constipation or
diarrhoea within 24 hours after using this plant.
Interestingly, this species is also used widely across Africa as medicine by
many traditional human societies. Chemical investigations of compounds which
are effective against illness caused by bacterial infection, bilharzia, cancer,
Whole leaf-swallowing : Aspilia mossambicensis
Chimpanzees use their lips to carefully remove one leaf from the plant at a
time and pull it into the mouth with the tongue. This causes these rough,hairy
leaves to fold up accordion-style. Each folded leaf is then swallowed whole
without being chewed. Leaves are evacuated whole and undigested in their feces.
It has recently been demonstrated that leaves swallowed in this manner
physically remove adult worms that were previously attached to the wall of the
large intestine. As many as 21 worms have been found trapped within the folds
and attached to the surface of these leaves.
Leaves are now known to be swallowed whole by chimpanzees, bonobos, and
lowland gorillas across Africa. The hairy, rough texture of the leaf is a
characteristic common to 19 species now known to be used in this way.
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