Effects of shell condition and size upon the shell choice behavior of a hermit crab

Hermit crabs attracted to simulated sites of predation upon gastropods, a source of empty shells, were more likely to inhabit shells of worse condition than crabs collected by visual searches, suggesting that shell condition affects shell choice behavior. Laboratory tests showed that Pagurus pollicaris Say inhabiting shells with lip damage, hydroid colonies, and pitting by boring organisms exchanged shells more frequently than crabs in unmodified shells. Shell fit also affected laboratory shell exchange; i.e., crabs in relatively small shells exchanged significantly more than crabs in relatively large shells. The shell conditions inducing the highest observed rates of shell exchange were those potentially increasing the risk of predation: lip damage, relatively small shells, and shells weakened by boring organisms. The active shell exchange behavior induced in crabs inhabiting damaged, pitted, and fouled shells explains the overrepresentation of these shell conditions at predation events where the probability of shell exchange is high.