The capability to seek out medicinal plants was thought to be limited to creatures with advanced brains; for instance, chimpanzees harboring intestinal worms swallow bristly leaves to scrape the parasites from their guts. Now researchers at Wesleyan University and their colleagues find that woolly bear caterpillars (Grammia incorrupta) also self-medicate when ill. Caterpillars infested with parasitic fly maggots ate roughly twice as much alkaloid (specifically, pyrrolizidine alkaloid) as uninfested ones; such toxins naturally exist in bloodroot and other caterpillar food plants. As a result, roughly 20 percent more of the infested caterpillars survived into adulthood as compared with infested caterpillars that did not munch on the medicine. The findings, the first known instance of invertebrate self-medication, appear in the March 10 PLoS ONE.