Among polygynous species, males often compete for the possession of mating sites to increase their reproductive success. Weaker individuals frequently adopt alternative non-territorial mate-locating tactics, but the adoption of alternative territorial tactics may also occur. Although alternative tactics with territory defence are less common in arthropods, factors that drive its adoption may provide information to understand the organization of different territorial mating systems in the group. Here we investigate the adoption of resource-based territoriality as an alternative to a non-resource-based one by males of the butterfly Paryphthimoides phronius. Male P. phronius commonly defend sunny clearings lacking feeding resources in the forest edge (non-resource-based territoriality). However, after experimentally offering fermenting fruit in previously undefended sites, we showed that males also adopt a resource defence tactic. Males in territories with fermenting fruits apparently feed on this resource when they are not defending the territory. However, males in sites without resources did not migrate to territories with resources when given the opportunity. To our knowledge, this is the first experimental investigation to show a non-resource- and an alternative resource-based mate-locating tactic in a butterfly. We suggest that this behavioural flexibility may represent an important step to understand the ecological factors responsible for the organization and evolution of different territorial mating systems in insects.