Animal self-medication

Great apes and many other animal species are known to make use of therapeutic plants. In the journal Science, biologist Jaap de Roode makes a case for more research on this topic.
Research on self-medication is largely the domain of primatologists; the idea is that higher cognitive ability is necessary for this behaviour. It has proved difficult to combat the image of a chimpanzee searching the jungle for a plant to help cure its diarrhoea. Yet de Roode and his colleagues believe that self-medication is much more common in the animal kingdom than has previously been thought, including in unexpected species such as birds, ants, caterpillars / butterflies and fruit flies.

The Science article distinguishes between preventive and therapeutic self-medication. Baboons, for example, eat poisonous berries in order to prevent parasite infection during the wet season. Caterpillars eat plants containing poisonous alkaloids when they are plagued with the tachinid maggots that threaten to consume the insects from the inside out.

Self-medication behaviours can also benefit a following generation. Butterflies infected with single-celled parasites lay their eggs much more frequently on plants with high concentrations of cardenolides. After emerging from their cocoons, the caterpillars that eat the plants and take in these poisonous cardenolides are much less likely to be bothered by the parasites. Fruit flies also employ this strategy: when ichneumon wasps are around, the flies are more likely to lay their eggs in food with high alcohol content, which protects the larvae from the wasps. Other species to help themselves to nature’s healing ingredients are ants and bees, which drag tree resin containing antiparasitic chemicals into their nests to protect their young.

De Roode also sees evidence that, through self-medication, animal immune systems are extended to include chemicals present in plants. This saves the enormous energy an immune system requires of an insect’s body. The scientist compares this to other energy-intensive, superfluous systems that disappear over time – such as the eyes of a cave-dwelling fish, or our own tails.

The biologist writes that more research is necessary on this topic, and that this could be of import to humans. Chemical analysis of twenty-four plant species that wild chimpanzees eat revealed compounds with antibacterial properties, and also substances that combat malaria and leishmaniasis. Five of the extracts were found to be toxic to human tumour cells. These discoveries would appear to provide sufficient rationale to take this research domain seriously.