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We studied the ant-feeding behavior of Asiatic black bears (Ursus thibetanus) through direct observation in the Ashio area of Japan. We recorded the bears’ “time foraging per ant nest” (TPN), documented the seasonal occurrence of ants in their scats, estimated phenological changes in caste composition of the nests of two abundant ant species (Lasius flavus and L. hayashi), and calculated the nutritional composition of queens, males, workers, queen pupae, and non-queen pupae of both species. We addressed two main hypotheses: (1) ant-nest phenology, especially the availability of pupae, affects bears’ myrmecophagy level; and (2) TPN changes according to the caste composition of ant nests. Bears in the Ashio area consumed more ants than in previous studies elsewhere in Japan, with consumption peaking in early July. The availability of pupae may trigger ant feeding by bears. And, because queen …