While the adults feed on flower nectar, the females insert their eggs into the eggs of certain kinds of caterpillars (Pyralidae, Gelechiidae, Tortricidae). The host egg is not killed; the host larva is allowed to continue to grow until it reaches a stage compatible with the maggot-like parasite's needs for its own development. At that stage, the parasitic larva emerges from the host's body and continues to feed on it from the outside. When the parasite completes its larval development, it spins a cocoon within the cocoon or pupation chamber of the host. When the adult emerges, it must cut through all these layers with its mandibles.

Ever see the movie "Alien?"

from the Zimlich Zone Foundation