The genus Paracyphononyx Gribodo, 1884 (Pompilidae) contains species that act as koinobiont parasitoids of cursorial spiders. Here, we record a new parasitism interaction involving the pompilid wasp Paracyphononyx scapulatus (Bréthes) and the hunter spider Trochosa sp. (Lycosidae), and we describe how the wasp develops on the spider. This study contributes new information about the interaction between koinobiont ectoparasitoid wasps and spiders, which probably arose independently in different groups of wasps.