Left Handed Rule

Upon walking through the tide pools of Diamond Head, multiple mollusks can be seen slowly creeping across algae covered rocks. Every now and then however one of these little snail shells seems to pick itself off and scuttle away at much too rapid a pace. Upon closer inspection of these speedy shells, a small crustacean can be observed cowering inside his hefty stolen home.

http://www.botany.hawaii.edu/basch/uhnpscesu/htms/kalainvr/fish_pops/diogenid/crab02.htm

The left handed hermit crab is one of the most common species of hermits in the Hawaiian tide pools. They are characterized by their bright blue eyes, white banded legs and a large left claw, hence the name “left handed”.  These adorable critters use their left hand as a sort of door to ward off intruders; when they feel threatened they quickly draw their bodies, legs and all, into their shell and block the entrance with the oversized appendage.

Just as any good homeowner should be, hermits are picky about where they choose to settle in. Most left handed hermits seem to prefer the shell of the pipipi (Nerita), top or turban snails. It is very rare for a hermit to kill a snail in order to get their home, most often they wander around until they find a suitable shell, then test it out with their legs and antennae. If it passes this first cursory inspection, the hermit will release its little hind legs from its current shell and pull its soft body quickly out of the old home and wedge itself into the new shell. Sometimes this second test proves that the shell is inadequate housing and the hermit returns almost immediately to its old shell.

The ability of these little crabs to survive is dependent on the number of shells present in the tide pools. That means every shell counts! So please, even if it looks like it would go nicely on your mantle: don’t take shells home from the beach. Shell removal displaces many of these crabs each year, so be courteous; some little hermit may thank you one day.

-Mireille Steck

 

Reference:

Waikiki Aquarium. Marine Profile: Tidepool Hermit Crabs. Education Department University of Hawaii-Manoa. <http://www.waquarium.org/_library/images/education/marinelifeprofiles/tidepoolhermit-web0909.pdf>.

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