Monarch Butterflies Prescribing Medicine for Offspring

Research at Emory University has revealed a shockingly sophisticated behavior in monarch butterflies: selective laying of eggs on medicinal plants when the egg-laying female butterfly is infected by a parasite. A team led by evolutionary biologist Jaap de Roode investigated patterns of egg laying by female monarchs in an attempt to determine when (and why) butterflies lay their eggs on more or less toxic or nontoxic species of milkweed (which serves as the food source for monarch larvae).

Based on previous research, the scientists knew the selection of milkweed plant was connected to avoiding predation. (Monarchs that consume toxic milkweed as larva are toxic for any predator even after the caterpillar matures into a butterfly.) De Roode, however, wondered if the egg-laying patterns could also be related to Ophryocystis elektroscirrha, a parasite that infects the monarchs throughout all life stages, is passed on through reproduction, and is potentially fatal.

A battery of experiments in the lab showed that infected monarchs preferred to lay their eggs on a toxic species of milkweed, whereas uninfected females selected species at random. “We have . . . found that infected female butterflies prefer to lay their eggs on plants that will make their offspring less sick, suggesting that monarchs have evolved the ability to medicate their offspring,” de Roode said. Of particular interest is that the mother butterfly does not benefit from laying eggs on toxic plants; only her offspring do.

Animals’ ability to medicate themselves has not been studied extensively, which inspires University of Michigan chemical ecologist Mark Hunter, who contributed to the findings. “Studying organisms engaged in self-medication gives us a clue as to what compounds might be worth investigating for their potential as human medicines,” he explained. The case of the pharmaceutical monarchs is thus another example of humans looking to learn from God’s incredible creation and a way that God has provided for and designed the monarch for living in a fallen world.