They require a host for their larvae to make it to adulthood. The female giant ichneumon wasp has one of the longest ovipositor (the organ used to deposit eggs) of any wasp, which can measure 12.7 to 15.24cm. They use this ovipositor to deposit their eggs deep into decaying wood where their preferred host, pigeon horntails (Tremex columba) larvae are found.
The larvae will feed on their host to obtain all the nutrition they will ever need. They overwinter as larvae and emerge as adults in spring. The adults will live about 27 days, just long enough to mate and continue the life cycle. The adults do not feed, and there is little competition between them. An adult will remain in a very small area during its lifetime, usually around many decaying logs and tre