Pagurus hirsutiusculus

Distinguished from co-occurring hermit crabs by the combination of dense body hair and banded appendages. Pagurus samuelis occurs higher in the intertidal and lacks the extensive hair covering. The white and blue leg bands and white-banded antennae are diagnostic. Southern populations (below Puget Sound) are less hairy and smaller, historically recognized as subspecies P. h. venturensis. The enlarged right cheliped and smaller left cheliped with calcium-sensitive setae are additional identifying features.

Marine; intertidal zone to subtidal depths of 110 m. Found in tide pools with sand or rock substrate, under rocks, logs, and seaweed. Occupies crevasses on bedrock and cobbled areas. In British Columbia, occurs from water line to approximately 2.5-3 m above Canadian chart datum. Generally occurs lower in the intertidal than Pagurus samuelis. Common in San Francisco Bay.

North Pacific: Pribilof Islands, Alaska to southern California; Bering Strait south to Japan. East Pacific and Indo-West Pacific regions. Core range includes British Columbia, Washington, Oregon, and California coasts.

Primarily detritivorous; opportunistic feeder consuming seaweeds and other available organic material.

• Eremitione giardi - parasiteBopyrid isopod ectoparasite inhabiting branchial chamber, feeding on hemolymph
• Peltogasterella sp. - parasiteColonial rhizocephalan parasitic barnacle
• Peltogaster sp. - parasiteRhizocephalan parasitic barnacle with internal root system and external reproductive externa; can manipulate host physiology
• Liriopsis pygmaea - hyperparasiteHyperparasite of Peltogaster sp.

Ovigerous females carry visible egg clutch on abdomen. Larval development includes planktonic stages. Peltogaster sp. parasite has dispersive larval stages and several invasion stages of single host. Eremitione giardi parasite involves intermediate host (likely copepod) and two separate free-living larval stages.

Occupies abandoned gastropod shells for protection; shell selection aided by calcium-sensitive setae on minor chela. Individuals from calmer waters readily abandon shells when disturbed by predators. Cannibalism observed in captivity. Emerges from shells when disturbed.

Detritivore contributing to nutrient cycling. Host for multiple parasite species including rhizocephalans and bopyrid isopods; parasite infections may mediate host population regulation and responses to environmental stress. Infected individuals show reduced survivorship following heat stress compared to uninfected individuals.

Common subject of intertidal ecological studies. Baseline population data from 1970-1971 San Francisco Bay survey used to assess long-term biodiversity shifts and invasive species impacts. Shell preference studies inform understanding of gastropod shell availability and hermit crab community dynamics.

• Pagurus samuelisCo-occurs in intertidal zone but occupies higher tidal levels; lacks dense body hair and distinctive leg banding pattern of P. hirsutiusculus
• Pagurus hirsutiusculus venturensisFormerly recognized subspecies for southern populations below Puget Sound; distinguished by reduced hairiness and smaller body size

• marine
• intertidal
• decapod
• hermit crab
• detritivore
• parasite host
• North Pacific
• shell-dwelling

• 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
• Marine biology | Blog - Part 2
• Parasites of the hermit crab Pagurus hirsutiusculus; distribution, prevalence, and thermal ecology.