Hermit crab study: Switching shells observed in terrestrial crabs.
Hermit Crabs Form "Gangs" to Evict Neighbors With Better Shells
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Oct. 27 2012 12:52 PM

Hermit Crabs Form "Gangs" to Evict Neighbors With Better Shells

Sometimes being the big man at the party is a bad thing.

Or at least so it is with hermit crabs. A Berkeley researcher has shown unusual social behavior in the pint-sized terrarium favorites, which seem to gather in small “gangs” to oust an unlucky peer from his shell.

When the crabs congregate, they form into a line based on their size, and the crab with the largest shell gets booted. Then, in tandem, each crab moves up into the next largest shell, giving them more room to grow. The unlucky big guy left without a home is then immediately vulnerable to a predator.


According to the research, the behavior is a rare example of social evolution from terrestrial hermit crabs, which, unlike their seafaring cousins, only have so many shells to choose from. Also hardly what you'd expect from something called "hermit."

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