The intricate nest building, cleaning and provisioning habits of the solitary hunting wasps Ammophila fernaldi Murray and A. pictipennis (Walsh) (Hymenoptera: Sphecidae) are supposed to have developed in response to parasite pressure. This paper presents the first study to record the behavior of phoresy of Paraxenos lugubris Pierce (Strepsiptera: Stylopidae). Adapting to the provisioning of single-cell nests of the Ammophila sp., it is the tiny, free-living, first instar larvae of P. lugubris, that are phoretic. They are carried, not by a wasp stylopized by a female P. lugubris producing first instar larvae, but by an unstylopized foraging wasp, thereby discreetly gaining entry to a single-cell nest before it is sealed. Multiple first instar P. lugubris larvae are often taken by the host, A. fernaldi and A. pictipennis, to the single egg/ larvae in the cell, resulting in superparasitism. These observations further demonstrate that Strepsiptera have developed mechanisms for parasitizing a range of hosts, including solitary wasps that develop in sealed cells.