The genus consists of robust species with a body length ranging from 4 to 10 mm. Characteristic morphological features include the meso- and metatibial pits (Figs 56–58), the enlarged metafemur (Figs 54–55), the apically bifid tarsal claw (Fig. 4) and, in some species the apicomedial tubercle on S4 of the female (Figs 59–60). Many species show sexual dimorphism, in which the mesosoma is strikingly bicoloured in the female (Fig. 47), but uniformly green, blue or violet in the male. The hosts are crabronid wasps of the subfamily Philanthinae. About 150 species are known worldwide, the majority of which occur in the Palearctic Region and Africa (Kimsey and Bohart 1991). The European fauna consists of 17 species and several subspecies, some of which probably would deserve species rank (Rosa and Soon 2012). Five species have been found in the Nordic and Baltic countries (Paukkunen et al. 2014).