Hermit crabs can perceive its body size when it adapts its body to changes in a complex environment. This ability is essential for animals to use tools or cross apertures. Here, we show that terrestrial hermit crabs, Coenobita rugosus, which frequently change shells, can perceive the inertial moment of their shells with attachment. Crabs crossed an aperture with shells of two different moments; Crabs with high moment more avoided the edge of the aperture than low. These results indicate that hermit crabs perceive the moment of carrying objects like as “dynamic touch” that human use when perceiving the extent of wielding objects.