Territorial residents usually win asymmetrical owner-intruder contests and a variety of hypotheses have been proposed to explain this phenomenon. In the butterfly Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae), male territorial residents defended their territories against intruders during numerous contests and kept them for many successive days. Field observations and experiments were conducted to examine the factors related to this superiority of residents. Forewing length did not differ between residents and intruders, suggesting that body size is not correlated with resource holding potential. Removal–replacement experiments demonstrated that residency did not serve as an arbitrary means for contest settlement, and did not support the recently presented alternative hypothesis that males with higher body temperature are more likely to win. New residents fought longer in defense of the territory as their residence duration in the territory increased. I discuss these results in light of game theory and suggest that the superiority of residents in C. smaragdinus may be based on the asymmetry of resource (territory) value for residents and intruders.