Parasitic wasp, coloured scanning electron micrograph (SEM). Parasitic wasps are parasitoids, parasites that always kill their host. Females lay their eggs in the body of another arthropod and when the larvae hatch they feed on the host from the inside out. Many parasitic wasps are considered beneficial because they control populations of agricultural pests. Magnification: x130 when printed at 10 centimetres wide.