Poisonous Partnership
Parasitoid wasps use viruses as a weapon
By David Shiga
The attack of a small black wasp doesn’t seem to faze the caterpillar that’s munching on the leaf of a maple tree—at least not at first. After getting stung, the caterpillar continues to crawl around and eat as if nothing happened. But 10 days later, it suddenly slows its crawl. It stops eating and eventually stops moving but remains attached to a branch. The dozens of eggs that the wasp injected into the caterpillar have hatched, and the wasp larvae are now eating their host alive. By the time the larvae burst out through the caterpillar’s skin, there is little else left of their victim.
The wasp responsible for this gory scene is called a parasitoid rather than a parasite. The distinction is that parasitoids kill their hosts, whereas parasites usually don’t. Parasitoid wasps aren’t familiar to most people because the creatures tend to be small and they lack the flashy stripes of their better-known wasp and bee cousins. But scientists estimate that there are hundreds of thousands of parasitoid wasp species, more than all the species of ants, bees, and nonparasitoid wasps put together.