For thousands of years indigenous peoples around the world have used plants for medicinal purposes. This knowledge was passed from generation to generation by shamans and healers who were most knowledgeable about medicinal plants and other indigenous cures. A major source of such medicinal plants is the rainforest, where indigenous populations make use of more than 5,000 plant species. Many of these medicinal plants have been used to produce our modern drugs and medicines. Today, nearly 70% of medicines come from nature, of which more than 25% come from rainforest plants.

In addition to the ancient populations that have used medicinal plants to cure disease, we have discovered numerous examples of wild animals who also seek out specific plants for their medicinal benefits. In many cases, the same cures discovered by humans have also been used by wild animals to treat similar ailments.

Eating the whole tree is not an uncommon behavior in elephants

An extraordinary example is of a pregnant female elephant in Kenya’s Tsavo Park. After observing the very stable diet and feeding rituals of this particular elephant for nearly a year, ecologist H. T. Dublin was surprised to observe the pregnant elephant wandering much farther than usual, and not feeding until she came upon a small tree of a species related to borage that she had never been known to include in her diet before. Dublin watched as the elephant almost entirely devoured the tree. Four days later, she gave birth to a healthy calf. Further investigations by Dublin revealed that tea made from the leaves and bark of this tree induced uterine contractions and was often used by Kenyan women to induce labor or abortion.

Studies in the 1990s by Duke University zoologist Dr. K. Glander suggest that females of South America’s mantled howler monkey may be actively employing pharmacological methods to determine the sex of their offspring. Glander noted that the sex of a female’s offspring appears to be directly related to the plants she eats before mating. These plants affect the electrical conditions in the female’s reproductive tract by either attracting or repelling sperm carrying the male chromosome, which are believed to possess a different electrical charge than sperm carrying the female chromosome.

During a malaria outbreak in Calcutta in 1998, Dr. Dushim Sengupta and his colleagues at Calcutta’s Center for Nature Conservation and Human Survival were surprised to see house sparrows eating and lining their nests with leaves from the paradise flower tree, a species whose leaves are rich in the anti-malarial drug quinine. The sparrows swiftly gathered fresh leaves of this same species when the scientists removed those already lining their nests, confirming that their choice of leaves was deliberate.

House Sparrows utilize the leaves of the paradise flower tree to protect them from Malaria

In Brazil, female woolly spider monkeys have been observed intentionally consuming plants that affect fertility. Wisconsin University primatologist Dr. K. Strier noted that once a female monkey has given birth, she seeks out certain leaves that contain isoflavonoids, which reduce fertility. The same females eat a legume called monkey ear when they are preparing to concieve, which produces a steroid believed to enhance fertility.

Brazilian woolly spider monkeys use medicinal plants that affect fertility

In 1972 a field researcher in Gombe National Park in Tanzania noticed a chimpanzee had left the path to eat the leaves of a plant called Aspilia rudis. This was not part of chimpaanzees usual diet, and its leaves are rough and sharp with a very nasty taste. This chimpanzee had not only sought the plant out, but had eaten the leaves by rolling them up and carefully placing them in his mouth before swallowing. Other chimps were observed eating rough leaves from 19 different plants in the same way. It was eventually discovered that the leaves were excreted whole and, when examined closely, tiny worms that had infected the chimpanzee’s stomachs were found on the sharp barbs of the leaves. Researchers in the Gombe also learned that Aspilia leaves were used by indigenous herbalists for stomach upsets since they contained chemicals with antibacterial properties and also eradicated stomach parasites.

It appears that animals avoid medicinal plants unless they need them. At the Awash falls in Ethiopia there are two baboon populations, one above the falls and one below. The tree Balanites aegyptiaca, the fruit of which is used by the locals as a de-worming treatment, grows in both areas. However, it is only consumed by the lower baboons, who are exposed to a parasite spread by water snails.

There is also evidence that various animals will seek out plants that provide an intoxicating effect. It is well known that elephants can smell the fermenting fruit of the marula tree from 10 kilometers and will come running for it. Bohemian waxwings enjoy rowan berries that have begun to ferment. These birds are often found dead on the ground after falling from their perch. Postmortem examinations have shown they were drunk when they died.

Bohemian Waxwings enjoy fermented White Rowan Berries

Whether this knowledge comes from instinct or experience or a combination of both, it appears that over time, natural selection has favored those animals who are able to maintain their health through the use of medicinal plants in their environments. Zoopharmacognosy, or animal self-medication is a fascinating new field in biology that studies the self-medication of animals and what we can learn from them.

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