The house mouse (Mus musculus) is a small rodent widely distributed in human-inhabited environments around the world and is found throughout almost all of Japan. It originally nests in rock crevices or underground but also adapts to buildings. Its body is small and omnivorous, consuming seeds, plant material, insects, and human food, and it has a habit of storing food in its nest. It is mainly nocturnal and has very high reproductive capacity, breeding multiple times per year with a short gestation period. Because of its broad distribution, it is a species of low conservation concern.