Interspecific interactions among herbivorous insects are mainly mediated by food plant responses. On the other hand, under the circumstance that food plant depletion often occurs, one would expect an exploitative competition to occur between organisms sharing that food plant. We studied an exotic butterfly Sericinus montela and native one Atrophaneura alcinous sharing the same host plant Aristolochia debilis, which is not abundant food. In the field survey, leaves of A. debilis were frequently consumed completely by these caterpillars, but they often re-grew after some time and then were eaten by other caterpillars. Such plant regrowth occurred in various time and space, resulted in creating large variety of leaf density, i.e. availability of resources, among plant individuals. Thus, food supply is always present, and temporal and spatial heterogeneity of food plant availability may relax the competitive interaction between the two butterfly species. This study suggests that, when considering plant growth after herbivory, the lower abundance of food plants does not directly result in exploitative competitions among herbivorous insects.