Common Hermit Crab

Geographical Origin and Habitat: Widely distributed in the North Atlantic Ocean, North Sea, Baltic Sea, and down to the western Mediterranean. Found in rocky tide pools and seafloors down to 100 m.

Taxonomy: Member of the family Paguridae. Distinguished by its right claw, which is significantly larger and more robust than the left. Grows to approximately 8 cm in total length.

Social Behavior: Highly active and curious. Constantly scavenges the substrate for organic matter. Juveniles occupy shallow intertidal zones, while larger adults migrate to deeper waters.

Coloration and Sexual Dimorphism: Body color ranges from light orange to reddish-brown. Claws feature pale, granular bumps. Oval dark eyes on short stalks. No visible external sexual dimorphism.

Tank Setup: Must be kept in a coldwater or temperate marine setup with a chiller. Provide a sandy or fine gravel substrate and empty gastropod shells (e.g. Littorina for young, Buccinum for adults).

Diet and Feeding: Omnivorous scavenger and detritivore. Accepts frozen foods (mysis, brine shrimp, chopped seafood), pieces of mussels, small fish, and sinking pellets.

Water Quality: Essential to keep water cool (8-18°C). Tropical temperatures are lethal. Salinity SG 1.024-1.026, pH 7.9-8.4. Sensitive to copper treatments and elevated nitrates.

Compatibility and Tankmates: Not reef-safe. Suitable only for coldwater marine tanks. May prey on live snails if empty shells are lacking. Peaceful with larger, cool-water fish.

Aquarium Breeding: Females incubate eggs under their abdomen. Microscopic larval stages are pelagic and complex, and do not survive standard home aquarium filtration systems.

Risks and Diseases: Overheating (above 20°C) causes rapid death. High stress and mortality if suitable replacement shells are unavailable during growth.