Revealed: Unexpected Social Life of Terrestrial Hermit Crabs

Researchers at Tuft’s University and the New England Aquarium have uncovered an amazing example of social behavior among the common pet trade Terrestrial or Land Hermit Crab (Coenobita clypeatus).

Crab Real Estate Markets

Hermit Crabs protect the soft parts of their bodies by moving into the discarded shells of snails and other creatures.  Finding the right-sized home is a matter of life and death, as shell-less crabs are quickly eaten by predators.  It is also a constant concern for the crabs – as they grow, they need to find increasingly larger shells.

Deprived of shells, the crabs will try anything – one researcher described as “pathetic” their attempts to shelter within bottle caps and pen tops!

One Empty Shell Benefits a Colony

Writing in the May-June edition of Behavioral Ecology, biologists describe a Hermit Crab social behavior that has been coined the “Synchronous Vacancy Chain”.

When a crab finds an overly large shell, it waits nearby rather than moving off in search of a better fit.  Over a period that may span hours, other crabs gather around the shell and, amazingly, line up in size order (largest to smallest), clinging to one another’s shells.  Then, as if a switch were flipped, the largest crab moves into the empty shell, the next largest into the newly vacated shell and so on down the line.  In a few minutes, all the crabs have new, slightly larger homes that will better accommodate them as they grow!  One empty shell thus benefits many rather than a single crab.

Observing and Caring for Hermit Crabs

I’ve kept Terrestrial Hermit Crabs in group situations, including large zoo exhibits, but have not noticed this behavior, which primarily occurs at night.  This finding really highlights how much we have to learn about even the most commonly kept animals.  Please watch your pets closely (a Night Viewing Bulb may be useful) and write in with your observations; I’ll be sure to share what you learn with other readers.

Hermit Crabs have, potentially, very long lives…but only if given proper care.  Please check out our extensive line of foods, terrariums, heaters, substrates and other Crab Care Products.