HERMIT CRABS: SHELL-DWELLERS WITH MOBILE HOMES

As everyone knows, Hermit Crabs get their name from the fact that from an early age they borrow empty seashells to live in. As they grow they trade up to a bigger one, leaving their previous home for a smaller crab to move into. It’s a benign** chain of recycling that the original gastropod occupant would no doubt approve of, were it still alive… The crabs are able to adapt their flexible bodies to their chosen shell. Mostly they are to be found in weathered (‘heritage’) rather than newly-empty shells for their home. [**except for fighting over shells] 

 HERMIT CRAB FACTS TO ENLIVEN YOUR CONVERSATION

• The crabs are mainly terrestrial, and make their homes in empty gastropod shells
• Their bodies are soft, making them vulnerable to predation and heat.
• They are basically naked – the shells protect their bodies & conceal them from predators
• In that way they differ from other crab species that have hard ‘calcified’ shells / carapaces
• Ideally the shell should be the right size to retract into completely, with no bits on display

• As they grow larger, they have to move into larger and larger shells to hide in
• As the video below shows wonderfully, they may form queues and upsize in turns
• Occasionally they make a housing mistake and chose a different home, eg a small tin

• The crabs may congregate in large groups which scatter rapidly when they sense danger
• The demand for suitable shells can be competitive and the cause of inter-crab battles
• Sometimes two or more will gang up on a rival to prevent its move to a particular shell

HERMIT CRABS CAN EVEN CLIMB TREES – WITH THEIR SHELLS ON TOO

Credits: All photos taken on Abaco by Keith Salvesen except for the tree-climber crab photographed by Tom Sheley; video from BBC Earth