I read a recent article in New Scientist about animals that know how to self-medicate using materials (often plants) found in their environment.
Most of us know about how monarch butterflies lay their eggs on native milkweed plants that the larvae (caterpillars) then eat. Milkweed leaves contain very toxic chemicals which, in turn, means the caterpillars (and adult butterflies) become toxic to predators.
Scientists have noted chimpanzees infested with intestinal worms deliberately seek out a certain plant with leaves that are rough like Velcro. The chimps fold the leaves and swallow them whole, rather than chewing them. The worms in the gut get caught on the leaves and are passed out in the feces.
We know that chimps are quite intelligent, but it is harder to imagine that other creatures, such as butterflies, infested with parasites deliberately search for milkweeds with higher levels of the toxic chemicals than normal. A study done with monarchs demonstrated that the mother butterfly infested with parasites searches out and lays her eggs on “medicinal milkweed” i.e. milkweed with higher concentrations of the toxic chemicals.
Other examples of animals self-medicating include sheep infected with worms preferring to eat plants containing more tannins that kill the worms. Once the worms have gone, the sheep stop eating those plants.
A particularly amusing and a more modern adaptation is the “birds and butts” story. Researchers in Mexico studying how urbanization affects bird nesting discovered that nests of house finches contained a lot of unknown white fluff. It was not known why the fluff was there, but when it got wet after a rain, it smelled of cigarette smoke.
The researchers realized the white fluff was from cigarette butts. Nests with more butts had fewer lice, mites and ticks.
This was not an accidental occurrence. When the butts were removed by researchers, the nests became infested with lice and other parasites. After the butt removal the house finches actively collected more cigarette butts to bring back to the nests, thus reducing the parasite infestation.
We grew up knowing house cats needed to eat grass occasionally to help them regurgitate intestinal worms, but I did not know, that cats rolling around in catnip was not just for pleasure. According to Japanese cat watchers, cat hair covered in catnip repels mosquitoes.
Maybe I should try rubbing my face and hands with catnip from now on.
