Zoopharmacognosy is a behaviour in which non-human animals apparently self-medicate by selecting and ingesting or topically applying plants, soils, insects, and psychoactive drugs to treat or prevent disease.
The term derives from roots zoo ("animal"), pharma ("drug"), and gnosy ("knowing") and was proposed in 1993. The term gained popularity from academic works and in a book by Cindy Engel called Wild Health: How Animals Keep Themselves Well and What We Can Learn from Them.
A well-known example of zoopharmacognosy occurs when dogs eat grass to induce vomiting. However, the behaviour is more diverse than this. Animals ingest non-foods such as clay, charcoal and even toxic plants, apparently to prevent parasitic infestation or poisoning. Self-medication in wild animals remains a controversial subject because evidence is mostly circumstantial or anecdotal, however, there are many purported examples. The methods by which animals self-medicate vary, but can be classified according to function as prophylactic (preventative, before infection or poisoning) or therapeutic (after infection, to combat the pathogen or poisoning).
Many examples of zoopharmacognosy involve an animal ingesting a substance with potential medicinal properties. Some animals ingest the substance when they appear to be well, suggesting the behaviour is preventative or prophylactic. In other cases, animals ingest the substance when unwell, suggesting the behaviour is therapeutic or curative.
Wild chimpanzees with upset stomachs seek whole leaves of the Aspilia plant. These contain thiarubrine-A, a chemical active against intestinal nematode parasites. The chimpanzees pick the Aspilia leaves and roll them around in their mouths, rather than chewing, before swallowing the capsule-like leaves whole. They swallow as many as 15–35 Aspilia leaves in each bout of this behaviour, particularly in the rainy season when there are many parasitic larvae leading to an increased risk of infection. Chimpanzees have learned to distinguish between harmful plant parts and parts that contain beneficial compounds. They learn this behaviour from other group members, in a form of social learning. Chimpanzees, bonobos, and gorillas eat the fruits of Aframomum angustifolium—laboratory assays of homogenized fruit and seed extracts show significant anti-microbial activity.
As well as whole-leaf swallowing, chimpanzees select bitter leaves for chewing. It was noted that infection of parasites drops noticeably after chimpanzees chew leaves of pith (Vernonia amyddalina), which have antiparasitic activity against schistosoma, plasmodium and Leishmania. Chimpanzees don't consume this plant on a regular basis, but when they do eat it, it is often in small amounts by individuals that appear ill.
Jane Goodall witnessed chimpanzees eating particular bushes, apparently to make themselves vomit. There are reports that chimpanzees swallow whole leaves of particular rough-leaved plants such as Aneilema aequinoctiale; these remove parasitic worms from their intestines. Illustrating the medicinal knowledge of some species, apes have been observed selecting a particular part of a medicinal plant by taking off leaves then breaking the stem to suck out the juice.
Anubis baboons (Papio anubis) and hamadryas baboons (Papio hamadryas) in Ethiopia use fruits and leaves of Balanites aegyptiaca to control schistosomiasis. Its fruits contain diosgenin, a hormone precursor that presumably hinders the development of schistosomes.
African elephants (Loxodonta africana) apparently self-medicate to induce birth by chewing on the leaves of a particular tree from the family Boraginaceae; Kenyan women brew a tea from this tree to induce childbirth.
White-nosed coatis (Nasua narica) in Panama take the menthol-like smelling resin from freshly scraped bark of Trattinnickia aspera (Burseraceae) and vigorously rub it into their own fur and/or that of conspecifics, possibly to kill ectoparasites such as fleas, ticks, and lice, as well as biting insects such as mosquitoes. A chemical study of the resin has revealed the presence of the triterpenes α - and β-amyrin, the eudesmane derivative β-selinene, and the sesquiterpene lactone 8β-hydroxyasterolide.
Domestic cats and dogs often select and ingest plant material, apparently to induce vomiting.
Ruminants appear to learn to self-medicate against gastrointestinal parasites by increasing consumption of plant secondary compounds with antiparasitic actions. This selective feeding improves health and fitness.
Standard laboratory cages prevent mice from performing several natural behaviours for which they are highly motivated. As a consequence, laboratory mice sometimes develop abnormal behaviours indicative of emotional disorders such as depression and anxiety. To improve welfare, these cages are sometimes enriched with items such as nesting material, shelters and running wheels. Sherwin and Olsson tested whether such enrichment influenced the consumption of Midazolam, a drug widely used to treat anxiety in humans. Mice in standard cages, standard cages but with unpredictable husbandry, or enriched cages, were given a choice of drinking either non-drugged water or a solution of the Midazolam. Mice in the standard and unpredictable cages drank a greater proportion of the anxiolytic solution than mice from enriched cages, indicating that mice from the standard and unpredictable laboratory caging may have been experiencing greater anxiety than mice from the enriched cages.
Many parrot species in the Americas, Africa, and Papua New Guinea consume kaolin or clay, which both releases minerals and absorbs toxic compounds from the gut. Great bustards eat blister beetles of the genus Meloe to decrease the parasite load in the digestive system. Cantharidin, the toxic compound inside of blister beetles, can kill a great bustard if many beetles are ingested.
Some animals apply substances with medicinal properties to their skin. Again, this can be prophylactic or curative. In some cases, this is known as self-anointing.
North American brown bears (Ursos arctos) make a paste of Osha roots (Ligusticum porteri) and saliva and rub it through their fur to repel insects or soothe bites. This plant, locally known as bear root, contains 105 active compounds, such as coumarins that may repel insects when topically applied. Navajo Indians are said to have learned to use this root medicinally from the bear for treating stomach aches and infections.
More than 200 species of song birds wipe ants through their plumage in a behaviour often called anting. Birds grasp ants in their bill and wipe them vigorously along the spine of each feather down to the base. Sometimes, they roll in ant hills twisting and turning so the ants crawl through their feathers. Birds most commonly use ants that spray formic acid. In laboratory tests, this acid is harmful to feather lice. Its vapour alone can kill them.
Some birds select nesting material rich in anti-microbial agents that may protect themselves and their young from harmful infestations or infections. Examples include European starlings (Sturnus vulgaris) lining their nests with wild carrot (Daucus carota) and house sparrows (Passer domesticus) with materials from the neem tree (Azadirachta indica). House sparrows have also been observed to change from neem to quinine-rich leaves of the Krishnachua tree (Caesalpinia pulcherrima) during an outbreak of malaria; quinine controls the symptoms of malaria.
Value to humans
- "Some of the compounds we've identified by zoopharmacognosy kill parasitic worms, and some of these chemicals may be useful against tumors. There is no question that the templates for most drugs are in the natural world."
- 2002 British documentary television series Weird Nature episode 6 Peculiar Potions documents variety of animals engaging in intoxication or zoopharmacognosy.
- Effect of psychoactive drugs on animals
- List of abnormal behaviours in animals
- Pica (disorder)
- Wound licking
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- Engel, Cindy (2002). Wild Health: How Animals Keep Themselves Well and What We Can Learn from Them. Harcourt Mifflin Harcourt, New York.
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- BBC Weird Nature (6-6) - Peculiar Potions part 1 / 3