Abstract  Parasitism by Buathra tarsoleuca (Schrank) of Ammophila sabulosa (L.) and Podalonia affinis (Kirby) nests was studied by means of a frame-by-frame analysis of video recordings obtained in the field. We describe behavioral patterns (with some additional ecological notes) during host detection and provide a schematic diagram for the sequence of events involved in this process. Using scanning electron microscopy, we have found morphological details in the antennae, ovipositor sheaths, and ovipositor of B. tarsoleuca which we suggest are involved in parasitism. The possible parasitism of the same hosts by two other ichneumonid wasps, Cryptus sp. and Meringopus calescens (Grav.), is discussed.