Members of this genus are characterised by the broadly open marginal cell, the U-shaped projection on the lower mesopleuron, the dentate segments of the ovipositor, and the frons with two rounded, flattened and usually striate areas particularly in the male (Kimsey and Bohart 1991). The medial cell of the forewing is asetose. The larvae are nest parasites of solitary vespids of the subfamily Eumeninae (e.g. Pterocheilus Klug and Hemipterochilus Ferton). The genus consists of 15 Palearctic species, most of which are found in northern Africa, Middle East and central Asia. In Europe, seven species are known (Rosa and Soon 2012), of which one, S. unicolor, is recorded from the Nordic and Baltic countries (Paukkunen et al. 2014).