When we fall ill, we visit a clinic or a pharmacy. Our ancestors however, picked their medicine from the wild. No pharmacist wrote prescriptions. Instead, our ancestors observed and learned from sick animals that healed themselves by eating certain plants. Yet, only in the past two decades have biologists and chemists begun to recognize that animals do self-medicate—select and use substances specifically to cure themselves of parasites and ailments… …
For more, check out my story for The Crux–Discover Magazine Online on how chimps, goats, fruit flies and civets qualify as pharmacists.
And for that “scenes cut out from movie” kind of thing, here’s the paragraph on Grammia incorrupta that was too long for the Discover story:
Plants have long waged chemical warfare against herbivores, deterring them with an arsenal of foul-tasting or poisonous biochemicals. In response, insects—most of them herbivores—have evolved to exploit the plants’ chemicals as medicine.
The black-and-orange caterpillars of the articiine moth, Grammia incorrupta, are hunted by parasitic flies and wasps called parasitoids. These parasitoids deftly inject their eggs into the caterpillars, turning the caterpillars into food vans for their children. The parasitoid larvae feed and grow within the caterpillar to eventually emerge as an adult, killing the caterpillar in their wake.G. incorrupta eats from many plant species. Some of these plants contain pyrrolizidine alkaloids (PA) which G. incorrupta can convert into non-toxic forms and keep, though the caterpillar’s survival suffers if it consumes too much PA.
However, Michael Singer, associate professor at Wesleyan University, found that parasitized G. incorrupta caterpillars eat a lot more PA, sometimes one-fold more than unparasitized ones. Adding PA into the diet improves the survival of parasitized G. incorrupta caterpillars but not of unparasitized ones. Through some yet unknown mechanisms, PA impedes the development and growth of parasitoid larvae. Singer and his colleagues have demonstrated the first self-medication behavior in insects.
In contrast to chimpanzees and lambs, G. incorrupta caterpillars do not learn to self-medicate. (They are likely too busy eating for lessons!) Instead, G. incorrupta reacts innately to the intruder in its body: the parasitized caterpillar’s taste cells acquire a heightened excitement towards PA, which then stimulates the caterpillar to eat more of the compound.
If you are keen on reading more about G. incorrupta, try Carl Zimmer’s earlier post, also on Discover Magazine.