The Behavioral Ecology of Hermit Crabs

Abstract

Hermit crabs are anomuran decapod crustaceans that have adapted to occupation of empty snail shells (and a few other types of cavities). Lack of calcification of the abdominal exoskeleton both allows and dictates the occupation of shelter not produced by the crabs themselves. Many animals utilize exogenous shelters, but almost all 800 species of hermit crabs are mobile while sheltered. The combination of mobility and protection afforded by this life style must contribute to the large numbers of these crustaceans found in virtually all marine environments, as well as on tropi­ cal terrestrial shores. The strong association between these crabs and their adopted shelters has greatly influenced almost all aspects of their biology. In most species, meta­ morphosis from larva to adult involves the assumption of morphological asymmetries associated with inhabitation of gastropod shells as well as behavioral changes as the free-swimming glaucothoe becomes a benthic, shell-seeking crab (3). Not surprisingly, most biological studies on hermit crabs have focused on the crab-shell association. Behavioral investigations on shell selection and shell exchange are obviously shelter-related, while the visual display systems utilized by these crabs (32, 46) are indirectly asso­ ciated with distribution of the shell resource. Most ecological studies have focused completely on the crab-shell interaction, and relatively little work has been done on the crabs as an element of marine ecosystems. Accord­ ingly, this paper only briefly reviews aspects of the crabs' behavioral ecology other than the crab-shell association and its influence on both individual behavior and population-related processes. While individual hermit crabs have been found in a variety of objects and some specialize in the use of scaphopod shells (some Py/opagurus spp.) (33) or even bamboo tubes