Abstract A field study was conducted to investigate the division of labour between queens and workers of Polistes fuscatus in colony defence against unrelated conspecific intruders. Responsibilities for colony defence resided primarily with the queen. Queens were significantly more likely than workers to encounter an intruder and to participate in the first interaction with an intruder. Queens also participated in the vast majority of interactions with intruders. However, queens did not display this same degree of differential involvement with returning nestmates. Queens also were significantly less tolerant than workers of both unrelated intruders and returning nestmates. These results and others suggest that queens have a more restrictive acceptance threshold than workers. The caste differences in acceptance thresholds appear to be consonant with the inclusive fitness interests of members of each caste. The field behaviour and ecology of P. fuscatus, together with theoretical considerations, lead to the prediction that queens should be more extensively involved than workers in colony defence against conspecific intruders.