 A single egg is laid per ootheca, into a host egg in some Evaniidae, and between the eggs in others.Some are able to oviposit even when the female cockroach still carries the fresh ootheca around, while other ensign wasps will only attack oothecae that are completed and have been dropped by the mother roach.The wasps seem to be able to determine if an ootheca is already used to host a larva, and refrain from depositing eggs in such cases; alternatively, the larvae might be cannibalistic, with the first to hatch in an ootheca eating any wasp eggs subsequently deposited.