Pagurus longicarpus

Distinguished from similar hermit crabs by the pronounced asymmetry of the claws, with the right claw markedly larger than the left. The distinctive claw stripes provide additional diagnostic characters. Shell occupancy in small gastropod shells (periwinkles, oyster drills) at small body size separates it from larger hermit crab species.

Body coloration varies, commonly gray, green, or white. The right claw is substantially larger than the left claw. Each claw bears a distinct tan or gray longitudinal stripe down the center. The abdomen is soft and asymmetrical, adapted to coil around the columella of gastropod shells.

Found in intertidal and subtidal marine environments. Occupies a variety of substrates. Occurs in shallow tidal pools during April through October, migrating to deeper, warmer waters during fall and winter. Tidal pool populations experience extreme fluctuations in temperature and salinity due to tidal inundation, solar heating, and freshwater input from precipitation.

Western Atlantic Ocean from Nova Scotia, Canada to northeastern Florida, USA. Gulf of Mexico coast from Florida to Texas. Established population reported in the North Frisian Wadden Sea (North Sea), likely introduced via trans-Atlantic larval transport in ballast water.

Active in shallow tidal pools from April to October. Moves to deeper waters during fall and winter months. Breeding season extends from late March through October, with peak activity in April.

Scavenger feeding on detritus, organic material from ocean surface foam, microcrustaceans, and algae. Feeding involves scooping substrate with chelipeds, tearing food, and passing it to mouthparts.

• Littorina spp. - uses empty shellperiwinkle shells
• Urosalpinx cinerea - uses empty shelloyster drill shells
• Ilyanassa obsoleta - uses empty shelleastern mud snail shells

Development includes planktonic larval stages: zoea, megalops, and juvenile, before reaching adulthood. Larvae are released into the water column where they undergo these stages prior to settlement. Females brood eggs within their shells; eggs attach to pleopods. Sexual internal fertilization requires both sexes to partially emerge from shells.

Intraspecific competition for shells is frequent and often aggressive. Larger individuals or those with suboptimal shells may forcibly evict occupants from preferred shells by grasping the resident's legs with their pincers. Shell size affects feeding behavior—individuals in improperly sized shells may cease feeding, leading to starvation. Shell selection influences growth rate and reproductive success, with larger shells correlating with higher reproductive output. Precopulatory mate guarding occurs, with males grasping female shells after detecting maturity pheromones.

Scavenger contributing to detritus processing in intertidal and subtidal communities. Shell occupation creates habitat for other organisms in empty shells. Serves as prey for birds, fish, snails, octopuses, and other crabs including the green crab (Carcinus maenas).

Used as bait in recreational fishing. Subject of ecological research on shell competition and intertidal community dynamics. Introduced population in European waters (Wadden Sea) represents a potential case study in marine invasion biology.

• Pagurus bernhardusLarger body size; occupies different shell types; different geographic range (Northeast Atlantic)
• Clibanarius erythropusBright red antennae and distinct eye stalk coloration; more timid behavior; different claw morphology

• marine
• intertidal
• scavenger
• shell-dwelling
• decapod
• invasive potential

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Amazing Story About What Entomologist Lynn Kimsey Recorded in San Francisco Bay 50 Years Ago | Bug Squad
• Marine invertebrates with Cornwall Wildlife Trust - Buglife Blog - Buglife
• hermit crab | Blog