Sheep
Usually not the sharpest tools in the shed, sheep are at least clever enough to keep their own health up by any means possible. If they are left to choose for themselves, they’ll always pick food that keeps them healthy. An example of this is that a sheep infected by parasites will eat more tannin-containing foods as that helps kill the parasites.
Wood Ants
That ants are smart creatures will surprise no one, but them living so closely together does come with the added dangers of diseases spreading quickly. In order to reduce the amount of harmful pathogens in their nests, they use a form of resin in them. Doing that actually increases the health of the entire colony, which is pretty insane.
Monarch Butterfly
The monarch butterfly is one of many types of small creatures that eats plants to boost their chemical resistance to a specific form of parasite. In this case they’ll eat milkweed to combat Ophryocystis elektroscirrha. That sounds like I made that up, but I didn’t. I promise.
