Ichneumon wasp. Coloured scanning electron micrograph (SEM) of the head of an ichneumon wasp (family Ichneumonidae) to show its long antennae. Ichneumon wasps parasitise 'host' organisms such as caterpillars and sometimes the larvae of other insects. The female lays her eggs inside the host's body, inserting them with her long ovipositor.The developing larvae eat the still-living host from within; once the larvae are fully grown, they leave the body and begin to spin their cocoons on the surface of the dead or dying host. Magnification: x130, when printed 10 cm wide.