Key to the Palaearctic species of Hercostomus exarticulatus group (males)

1. Fore and/or hind femora partly dark; hind tibia with weakly sclerotized triangular dorsolateral apical projection bearing minute spike; outer hypandrial arm with thick L-shaped curvation projecting ventrally; 2.5–3 mm ................................................ H. exarticulatus

– Femora entirely light yellow; hind tibia with strongly sclerotized triangular or ovate dorsolateral apical projection; outer hypandrial arm hidden, more or less straight, weakly curved at apex ...................................... 2

2. Hypandrium with 2 pairs of arms almost concealed, thin at apex; 1.8–2.2 mm ............................................................ ............................... H. exarticulatoides and H. vodjanovi

– Hypandrium with outer arm concealed and inner arm trapezoid, strongly projected distoventrally; 2.5 mm .... ........................................................................ H. canariensis