The common hermit crab is a fascinating crustacean that protects its soft, vulnerable abdomen by living inside empty gastropod shells — changing to larger shells as it grows throughout its life. Unlike true crabs, hermit crabs have a soft, asymmetric abdomen adapted to curl inside spiral shells, and their right claw is typically much larger than the left, functioning as a door to seal the shell opening when the animal retreats. Hermit crabs are social animals that participate in extraordinary ‘vacancy chain’ behaviors when a desirable empty shell becomes available.
About the Hermit Crab
Pagurus bernhardus
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💡 Fun Facts
01
When a vacant shell of a desirable size appears, hermit crabs form a 'vacancy chain' — a queue of up to 20 crabs that simultaneously exchange shells in a rapid chain reaction, with each crab moving into the shell vacated by the crab in front of it.
02
Hermit crabs can detect the chemical signature of a dead conspecific and will immediately investigate, as the dead crab's vacated shell represents a housing opportunity.
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Some hermit crabs cultivate sea anemones on their shells, which deter octopus predators with their stinging tentacles; in return, the anemones receive transport and access to food scraps from the crab's meals.
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The right claw (cheliped) is significantly larger than the left in most hermit crabs and functions as a 'door' that seals the shell entrance when the animal retreats, covering the soft abdomen from predators.
05
Hermit crabs possess gills for underwater breathing, but many species also have modified gills that extract oxygen from air — allowing them to forage on land for extended periods.
📍 Where to Find This Animal
Habitat Types:
Rocky Intertidal & Shallow Subtidal Zones
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