Anthrenus verbasci pupates in spring and the timing of pupation is controlled by a circannual rhythm. Although A. verbasci is considered to be a univoltine species in Japan, it is assumed that larval development in its natural habitats, including bird nests, varies with nutrient availability, and that the life cycle often takes two or more years to complete. In the present study, larval development and pupation times were compared under constant and outdoor conditions in larvae provided a diet of either high-nutrient bonito powder or low-nutrient pigeon feathers. Although a circannual pupation rhythm was observed irrespective of the diet used, larval development was slower on feathers than on bonito powder. The pupation times on feathers varied over three years or more under both constant and outdoor conditions. Under outdoor conditions, larvae grown on feathers needed three years to approach the weight gained within a year by larvae grown on bonito powder. It is considered that life cycle length in A. verbasci is often two years or more in nutritionally unstable natural habitats, and that this species has probably evolved a circannual rhythm as a seasonal adaptation to nutrient-poor environments.