Caught in the act!

I watched on Thursday morning as the larger of our two hermit crabs scoped out a new shell and then went for it! You don't get to see this very often, because it happens very quickly and only when a crab finds a suitable, available shell.

Hermit crabs are not true crabs -- they don't make their own shells. This leaves them extremely vulnerable to predation and injury, as their abdomens are soft and unprotected. To guard themselves, they use empty shells created by other animals -- a kind of recycling in the marine world! They're always on the prowl for a bigger and better shell. Once they find one of the right size, they hop in, backside first, and curl their abdomens around the columella, or middle column. They keep the shell with them at all times, carrying it around as their home. 

Because empty shells can be hard to come by, hermit crabs can be very competitive when it comes to obtaining one. The hermit crab in our tank has obviously succeeded in this many times, as it is big enough to need the shell of a moon snail, a very large gastropod that lives in Atlantic waters. Hermit crabs will outgrow their shells if they can't find or compete for bigger ones, and we at the tank have never seen a hermit crab this big!