There are so many fascinating stories about parasitic wasps that they have become a regular feature in this blog. Usually, their prey come off poorly in these tales, with caterpillars being reduced to little more than living, paralysed larders for macabre wasp grubs. But not always – some hosts don’t take the invasion of their bodies lying down. This post is an attempt to redress the balance between parasite and host, by telling the story of the caterpillar that fights back… with medicine.

One species of tiger moth, Grammia incorrupta, has a fuzzy caterpillar called the woolly bear. Like most other caterpillars, it’s exploited by several species of parasitoids including flies and wasps. If these body-snatchers lay their eggs inside a