What do wild animals do when they are sick?
Chimpanzees eat the same herbs that traditional healers in parts of Africa do to treat malaria and diarrhea. Baboons also eat certain kinds of leaves to cure infections; the leaves of one tree, the candelabra tree (Cassia), are sought out to treat menstrual cramps.
Not only those animals who have “high cognitive abilities that allow them to observe, learn, and make conscious decisions” can self-medicate, though, according to Mark Hunter, a University of Michigan ecologist, and his colleagues. Monarch butterflies and ants, fruit flies and moths are also “animal pharmacists,” who seek out certain plants for their curative effects.
Even more, these insects do not only use plants to treat their own maladies, but for those of others. Wood ants, the scientists found, take an antimicrobial resin from conifer trees and incorporate it into their nests, to ward off microbial growth in the colony. Monarch butterflies who have become infested with parasites protect their offspring from the same by laying their eggs on milkweed, which is anti-parasitic.
Says Hunter about these behaviors that seek to protect the animals’ future generations:
Perhaps the biggest surprise for us was that animals like fruit flies and butterflies can choose food for their offspring that minimizes the impacts of disease in the next generation. There are strong parallels with the emerging field of epigenetics in humans, where we now understand that dietary choices made by parents influence the long-term health of their children.
In the case of insects, using medication is an innate rather than a learned response. For instance, furry moth larvae known as wooly bear caterpillars have been observed to eat leaves of senecio (ragwort) to rid themselves of parasites. Eating these leaves fills them with alkaloids, which humans take in the form of caffeine, morphine and cocaine. Healthy wooly bear caterpillars also ingest small amounts of alkaloids so they become “unsavory” to predators — but if they eat too many, they can die.
The discovery that many types of insects self-medicate has a number of implications for “the ecology and evolution of animal hosts and their parasites,” says Hunter and his colleagues, as well as for understanding animal immune systems and our own.
Honeybees offer one example. From analyzing their genome, scientists have found that they do not have many of the immune system genes that other insects. Like wood ants, honeybees collect antimicrobial resins and put these into their nests. The honeybees have, it seems, evolved a way to compensate for not having such immune mechanisms. Or it might be that their reliance on “medicine” in the form of the resins has led to them losing some kinds of immune mechanisms.
“When we watch animals foraging for food in nature, we now have to ask, are they visiting the grocery store or are they visiting the pharmacy,” says Hunter. Plants are an important source of study to develop future medications, so observing which ones animals use to treat themselves could lead to the creation of new drugs for humans. To treat disease in ourselves, we’d do well to follow the flight of the butterfly.
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