Although two forms of Hercostomus plagiatus are separated in identification keys, both were considered to belong to one single species. My investigations, however, revealed that two distinct species were included. In this respect, H. plagiatus is redescribed, whereas H. verbekei sp.n. is described as new. Both species occur mainly in central and southern Europe; H. plagiatus is more common than its congener at nearly all sites investigated. Aspects of macro- and microhabitat preference, phenology and sex ratios in H. plagiatus are discussed. It is suggested that these two species are closely related. © 1993.