Key to West Palaearctic species of Hercostomus plagiatus group (males)

1 Antennal postpedicel clearly acute, about 1.5X as long as high; wing veins R4+5 and M1+2 parallel along most of their length, slightly convergent near wing apex; hypopygium with club-shaped cercus bearing several small, yellow scale-like inner setae along distodorsal margin; apicoventral epandrial lobe bearing 3 setae apically on knob (Pollet 1993, fig. 1)................................................................................................... H. plagiatus (Loew)

- Antennal postpedicel subtriangular, about as long as high; wing veins R4+5 and M1+2 parallel along most of their length or distinctly convergent towards wing apex (Figs 2, 3; Pollet 1993, fig. 2); hypopygium with ovoid or triangular cercus without scale-like setae; apicoventral epandrial lobe bearing 2 setae on its knob and 1 longer seta on stem..................... 2

2 Wing veins R4+5 and M1+2 distinctly convergent towards wing apex; hypopygium with ovoid cercus; epandrial lobe bearing seta on stem right before knob (Pollet 1993, fig. 2)................................................. H. verbekei Pollet

- Wing veins R4+5 and M1+2 parallel along most of their length, slightly convergent near wing apex; hypopygium with triangular cercus; epandrial lobe bearing very long seta at base of stem (Figs 3, 5, 6)...................... H. golanensis sp. nov.