Animals are continually confronted with disease and infection, but luckily the natural world is a veritable pharmacy. The study of what animals do when they are sick – called zoopharmacognosy – began in 1978.
“Self-medication can take many forms and occurs widely across the entire animal kingdom,” says primatologist Michael Huffman from Kyoto University in Japan. “But we still have a lot to learn in this area.”
To humans, eating dirt seems more likely to induce sickness rather than cure it. But giraffes (Giraffa camelopardalis) in South Africa eat mouthfuls of clay-rich termite mound soil to cure an upset stomach, as do elephants, chimpanzees, gorillas and rhinoceros.
This inspired scientists to perform mineralogical analyses on clay content – they found it is an effective binding agent and detoxifier with useful absorptive properties, meaning it could absorb and deactivate nasty toxins from bacteria or plants. It also contained the mineral kaolin, which is used in many human treatments for diarrhoea.
Take prenatal drugs
Huffman and his team saw pregnant sifakas (Propithecus verreauxi), a species of lemur in Madagascar, eating the leaves and bark of fig and tamarind trees in the weeks before giving birth. Small doses of these tannins stimulate milk production and kill gut parasites, and the group that ate the tannins had fewer failed pregnancies than a group of sifakas that didn’t.
Like something out of a horror movie, flies crawl inside the woolly bear caterpillar (Grammia geneura) and lay eggs. The caterpillar becomes paralysed and when the fly larvae hatch, they eat the caterpillar alive. But it has some defence.
In 2005, entomologists Elizabeth Bernays and Michael Singer from the University of Arizona reported that infected woolly bears seek non-nutritive leaves from threadleaf groundsel (Senecio longilobus). These leaves contain a toxic compound, pyrrolizidine alkaloids, which can kill parasitic fly larvae.
Just as we have our coffee in the morning, Chacma baboons (Papio Ursinus) in South Africa are known to occasionally consume a small quantity of leaves from Euphorbiaceae plants. These plants are not part of their regular diet. Researchers from the University of California, Davis classify them as ‘euphorics’ as baboons consumed them consistently but only in minute quantities. Euphorbiaceae plants are known for their stimulant properties, however, studies into the plant’s full pharmacological benefits are ongoing.
After a two-year pregnancy with a 100 kg calf, African elephants (Loxodonta africana) are eager to give birth. Twenty years ago, ecologist Holly Dublin from the WWF was observing the feeding routine of African Elephants in Kenya. She was surprised when a heavily pregnant female wandered out of her usual feeding area one day to munch on a different species of tree from the Boranginacae family. Days later she gave birth.
With more research, Dublin discovered that the leaves and bark of this tree induce uterine contractions and on some occasions pregnant Kenyan women would drink it in tea to induce labour or abortion.
Use insect repellent
Wedge-capped capuchin monkeys (Cebus olivaceus) that live in the tropical rainforests of Venezuela protect themselves from mosquitoes by using insect repellent. Instead of a bottle of spray, however, capuchins reach for a millipede (Orthoporus dorsovittatus) to rub over its body. Millipedes secrete benzoquinones, a potent insect repellent.
Irrigate their colon
Researchers from Kyoto University observed sick chimpanzees (Pan troglodytes) in the forests of Tanzania folding Aspilia leaves and swallowing them whole. The physical irritation produced by the bristly leaves on an empty stomach increases gut motility and secretion resulting in diarrhoea. This sheds the body of parasitic worms, a major cause of illness in chimps.
Fumigate their nests
Dusky-footed wood rats (Neotoma fuscipes ) that occupy forested areas in California engage in nest fumigation behaviour to control fleas, ticks and mites. Animals that rest in nests or burrows are particularly susceptible to nest-borne parasites that carry disease.
In 2002, researchers from Vassar College in New York showed that dusky-footed wood rats place bay leaves in their sleeping nests and regularly make tears in them to release fumigating vapours, significantly reducing parasite survival.
Soothe irritated skin
European starlings (Sturnus vulgaris) happily sacrifice ants to soothe their irritated skin and kill feather parasites. They collect and crush ants, then wipe them frenetically through their plumage. Ants secrete formic acid, which acts as a strong insecticide, fungicide and bactericide – enough to kill feather lice and mites. Formic acid also contains benzoquinones, which are powerful insect repellents. Such ‘anting’ is common in songbirds and has even been seen in squirrels, cats and monkeys.