ABSTRACT.The venoms of Polistes fuscatus (subspecies fuscatus) (F.) and P. exclamans Viereck from sympatric populations in North Carolina, U.S.A., contain a pheromone which attracts males and stimulates sexual behaviour in both conspecific and heterospecific males. Males of P. fuscatus (subspecies variatus Cresson), a subspecies from Wisconsin, respond to venom of P. fuscatus fuscatus, P. exclamans, and Vespula maculifrons (Buysson) from North Carolina, although the levels of response to P. exclamans and V. maculifrons venom are less than that to P. fuscatus variatus venom.Caged Wisconsin P. fuscafus males do not attempt to mate with P. exclamans females, but will attempt to mate with conspecifics. A series of bioassays indicates that males discriminate between females of P. fuscatus and P. exclamans on the basis of chemical, rather than behavioural or visual cues. The venom apparently is not important in species recognition. Instead, the results of two sets of bioassays suggest that species recognition is mediated by a surface pheromone on the cuticle of females.