In many cases, only the immature stage of a parasite feeds on the host, as illustrated here with a species that attacks aphids. A. An adult parasite lays an egg inside a live aphid. B. The egg hatches into a parasite larva that grows as it feeds on the aphid?s insides. C. After killing the aphid, the parasite pupates. D. The wasp chews a hole and emerges from the dead aphid, then flies off to find and parasitize other aphids.

Illustration by D. Kidd.