From corniculae to frontal shelves: A phrenological odyssey through the parasitic Hymenoptera

The majority of parasitic Hymenoptera possess rather 'typical' head capsules, with variation focused on the insertion point of the antennae, shape and size of the mandibles, and relative size of the compound eyes.  In a few taxa, however, extremely unusual head morphology has been observed, such as elongate, paddle-shaped mandibles, tridentate and “cow-catcher” clypeal protrusions, horn-shaped corniculae protruding from the frons and vertex, and entire heads shaped like an enormous wedge.  We provide a visual record of these rare and unusual taxa. We hypothesize that in some cases, these morphological adaptations are used in host searching, while in other cases, they are used for host emergence. Homoplasticity and sexual dimorphism of these features are discussed.