Passandridae, the "parasitic flat bark beetles," are a family of beetles notable for being one of the very few beetle families with larvae that are, as far as known, exclusively ectoparasitic on the immature stages of other beetles and Hymenoptera. Larvae are highly modified for their parasitoid habits. First instar larvae are heavily sclerotized, flattened, and spiny. Later instar larvae are physogastric (swollen posteriorly), with simple setae, short unsegmented legs, and reduced mouthparts.