We investigated the chemical components and energy content of Konara (Quercus serrata) acorns and their parasitic larval insect (Curculio dentipes). We then fed acorns to Japanese black bears (Ursus thibetanus) in captivity and monitored their eating behavior to evaluate the palatability of acorn cotyledons, parasitic larvae, and larval feces. We purchased 70kg of fresh acorns of Q. serrate and randomly selected 2512 of them and found that 17.7% of seeds were attacked by weevil larvae. The contents of protein and fat in the larval body were 28.6% and 53.7%, respectively. The gross energy of the larval body was 29.6kJ/DM g and the energy value was 1.8 times higher than that of acorn embryos. Our results suggest that the consumption of larvae parasitizing the acorns of Q. serrate contributes to the acquisition of animal protein and energy under incidental predation by large postdispersal acorn consumers, such as deer or wild boar. In addition, in our feeding experiment, bears discarded acorns filled with larval feces but showed much interest in living larvae and quickly consumed them finding them. This eating behavior shows that weevil larvae are highly palatable to bears, which may acquire animal protein and energy from them.