To test his hypothesis, first de Roode looked to see if infected larvae prefer to munch on the parasite-killing tropical milkweed species, rather than the swamp milkweed. They didn’t, so he concluded that the larvae do not use the tropical milkweed medicinally. But when he compared the behavior of healthy adult females with the behavior of infected adult females, a difference quickly became apparent. Infected females, which transmit the parasite to their offspring when they spawn, preferred to lay eggs on the tropical milkweed, showing that they can preemptively medicate their offspring. “Somehow, the mother knows what’s best,” de Roode says.
His findings challenge the view that only animals with cognitive complexity use medicine. If butterflies, which have a simple nervous system and no social structure, could preferentially use medicine, perhaps self-medication is pervasive in the animal kingdom and scientists just haven’t had the chance to find it yet.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.