Males display “inverse rapping” as a mating behavior to receptive females in the hermit crab Pagurus nigrofascia

: This paper describes “ inverse rapping ” as a characteristic mating behavior in Pagurus nigrofascia . The behavior involves one hermit crab pulling another crab ʼ s shell towards itself causing the shells to hit against each other. This is the first evidence that males perform inverse rapping as a mating behavior in a Pagurus species. Two experi-ments were conducted to describe the inverse rapping in detail and to discuss its function. In Experiment A, we clarified when (mating season or non-mating season) and to whom (males or females) males displayed this behavior. A focal male that had not been guarding in the field was placed together with another crab and their interaction was observed, especially inverse rapping. Males showed inverse rapping mainly with a female that was close to copulation in the mating season, especially when the male guarded the female. In Experiment B, we examined the female ʼ s response to male inverse rapping and tested the effect of the presence of a neighboring conspecific on the occurrence of the behavior. Most females reduced struggling and/or withdrew into their shells in response to male inverse rapping. The presence of neighboring crabs did not affect inverse rapping. Our findings suggest that inverse rapping is a mating behavior in P. nigrofascia , and that inverse rapping may benefit males in the initiation and/or continuation of precopulatory guarding because it can help to restrain struggling females. This behavior has not been observed in other sympatric Pagurus species and appears to be a characteristic mating behavior of P. nigrofascia .