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Carcelia iliaca (C. iliaca) is a parasitoid that is associated with Oak Processionary Moth (Thaumetopoea processionea; OPM).
C. iliaca parasitises older, almost full-grown OPM larvae inside or outside OPM nests and then completes its development by overwintering in a spent OPM nest before emerging the following spring.
Where C. iliaca is observed on OPM nests, caterpillars may appear agitated.
Bottom picture: credit The Royal Parks
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