If you keep a vegetable garden, there’s a fair chance you’ll encounter a grisly sight this summer. Some poor caterpillar will be clutching a leaf, with the pupae of parasitic wasps sprouting off its back. It has just died in a most grotesque way. A wasp has zeroed in on the caterpillar and injected eggs into its body. The eggs hatched, and the larvae devoured their hosts from within, keeping it alive until they were ready to emerge.

What makes this sight all the more grotesque is the fact that the plant the caterpillar is sitting on may have been an accomplice to the crime. When caterpillars nibble on plants, the plants sometimes respond by releasing a distinctive cocktail of chemicals.