Walking a beach, I picked up a nice shell to take home, a bright orange and blue topsnail – oops, something had already taken it and the little crab inside peered out at me angrily. I quickly put it back. Hermit crabs have soft shells and spirally curved abdomens so they can fit into empty mollusk shells. Since they lack hard exterior shells for protection, they must find a shell matching their size or perish. And as they grow, they need to abandon the old homestead and switch shells for a better fit, and competition among crabs for proper sized shells may be intense. Hermits often ‘gang up’ on another crab they perceive to have a better home, and then compete for the new digs after they’ve kicked out the original owner. These ‘decapod’ (meaning 10-footed) crustaceans are in the same family as crabs and shrimp, and eat by scavenging plant life in kelp and eel grass beds, dragging their shells with them as they go. Some older hermits may support a small stinging sea anemone to scare away predators (see the anemone on the lower inset drawing?), and the anemone benefits because it’s close to food fragments the hermit might drop.

Larry Eifert paints and writes about wild places. His work can be seen in many national parks across America – and at larryeifert.com. He’s currently at work in Sitka, Muir Woods and Olympic National Parks.

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