Laboratory studies of nestmate recognition (250.0 h of behavioral observation) were conducted on two species of paper wasps (Polistes). Gynes of P. carolina isolated from their natal nest and nestmates at emergence later failed to recognize nestmates, but gynes previously exposed only to their natal nest for 2 h recognized nestmates. Gynes of P. fuscatus previously (1) exposed to their natal nest and nestmates for at least 5d, (2) exposed only to their natal nest for 4.16–13.5 h and (3) exposed only to their natal nest for 1 h, all discriminated nestmates from non-nestmates. Thus, exposure to the natal nest is a sufficient condition for the ontogeny of nestmate recognition ability. Unrelated gynes of P. fuscatus, previously exposed to different fragments of the same but unrelated nest, also recognized each other. These results, together with the evidence from other recent studies, indicate that the mechanism of nestmate discrimination in Polistes has the following attributes. Recognition cues are (1) learned, (2) learned in the adult stage, (3) learned within a few hours of emergence with memories of these cues being durable if not permanent; thus, learning of recognition cues resembles imprinting; (4) Recognition cues are learned from the natal nest and/or brood and not from adult nestmates, (5) they cannot be visual, tactile, or auditory features of adult nestmates and thus are probably chemical, and (6) they can be both learned and acquired from a nest and/or its brood.