DISCOVERY: Animals Create Their Own Pharmacies

Many animal species have created their own pharmacies from ingredients that commonly occur in nature.

Birds, bees, lizards, elephants, and chimpanzees all share a survival trait: They self-medicate. These animals eat things that make them feel better, or prevent disease, or kill parasites like flatworms, bacteria, and viruses, or just to aid in digestion. Even creatures with brains the size of pinheads somehow know to ingest certain plants or use them in unusual ways when they need them.

Anyone who has seen a dog eat grass during a walk has witnessed self-medication. The dog probably has an upset stomach or a parasite. The grass helps them vomit up the problem or eliminate it with the feces.

The science of animal self-medication is called zoopharmacognosy, derived from the roots zoo (“animal”), pharma (“drug”), and gnosy (“knowing”). It’s not clear how much knowing or learning is involved, but many animals seem to have evolved an innate ability to detect the therapeutic constituents in plants. Although the evidence is entirely circumstantial, the examples are plentiful. The practice is spreading across the animal kingdom in sometimes surprising ways:

Neighborhood Pharmacy

A wide range of animals self-prescribe the plants around them when they need a remedy.

• • Bears, deer, elk, and various carnivores, as well as great apes, are known to consume medicinal plants apparently to self-medicate.
• • Some lizards are believed to respond to a bite by a venomous snake by eating a certain root to counter the venom.
• • Baboons in Ethiopia eat the leaves of a plant to combat the flatworms that cause schistosomiasis.
• • Fruit flies lay eggs in plants containing high ethanol levels when they detect parasitoid wasps, a way of protecting their offspring.
• • Red and green macaws, along with many animals, eat clay to aid digestion and kill bacteria.
• • Female woolly spider monkeys in Brazil add plants to their diet to increase or decrease their fertility.
• • Pregnant lemurs in Madagascar nibble on tamarind and fig leaves and bark to aid in milk production, kill parasites, and increase the chances of a successful birth.
• • Pregnant elephants in Kenya eat the leaves of some trees to induce delivery.
• Most studies of animal self-medication, however, are in the great apes. In the 1960s, the Japanese anthropologist Toshisada Nishida observed chimpanzees in Tanzania eating aspella leaves, which had no nutritional value. Harvard primatologist Richard Wrangham saw the same behavior at Jane Goodall’s Gombe reserve, where chimps were swallowing leaves whole. Other scientists noted the same in other chimp colonies. Without chewing, the animals weren’t getting much nutritional benefit. So why do it?
  In 1996, biologist Michael Huffman suggested the chimps were self-medicating. Huffman, an American who has worked for years in Japan at the Primate Research Institute at Kyoto University, first saw a parasite-ridden, constipated chimpanzee in Tanzania chew on the leaves of a noxious plant it would normally avoid. By the next day, the chimpanzee was completely recovered.
• The plants had bristly leaves, rough to the touch. Huffman theorized the chimps were swallowing the plants to take advantage of that roughness, using the leaves and stems to scour their intestines and rid themselves of parasites. Other researchers observed the same practice among other apes across Africa.
  Huffman established widely used criteria for judging when an animal is self-medicating. First, the plant eaten cannot be a regular part of the animal’s diet; it is used as medicine not food. Second, the plant must provide little or no nutritional value to the animal. Third, the plant must be consumed during those times of year—for example, the rainy season—when parasites are most likely to cause infections. Fourth, other animals in the group don’t participate . If the activity meets these standards, it is safe to assume the animal is self-medicating, Huffman says. Researchers have observed the practice in 25 regions involving 40 different plants.