Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Although many studies have evaluated the possible rules used by males to settle territorial contests, few have simultaneously considered the possibility of mutual or self-assessment of fighting ability and the effect of prior residence on the chances of winning. Here, we experimentally investigated the influence of previous residency on the development and outcome of contests between males of the butterfly Hermeuptychia fallax. By comparing the frequency of resident victories in nonmanipulated disputes versus interactions in which both rivals were induced to behave as residents, we showed that prior residency may interact with body mass in contest resolution. In nonmanipulated disputes, resident males showed high winning probabilities, although they were similar to losers in body mass. However, when both males behaved as residents, the disputes were longer and were settled in favor of the heavier male. This indicates that, although residency is an important component of male willingness to fight, it is not the only factor influencing conflict resolution. Despite the correlation between body mass and territorial success, the weight of neither winners nor losers correlated with fighting duration. We conclude that residence asymmetry may sometimes conceal male traits important to contest resolution and that it may obscure the identification of the assessment strategy used in contests.3016168Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)