Hanging Out with Hermit Crabs

If you visit a tide pool, you will most likely see a snail shell moving quickly over a rock. This behavior is suspicious-- what type of snail moves quickly? If you look closely, you will see a small crab poking its claws and beady eyes outside the shell. These animals are hermit crabs, shy snail impostors.

Hermit Crab Shell Games

When you think of crabs, you probably think of a hard shell. However, a hermit crab doesn't have a hard shell. Only its head and claws are tough and crusty. It cannot protect itself from predator animals in the tide pool, so it finds an empty, used snail shell.

A crab is choosy about its shell. It may try on five shells before it finds one that it likes. Once it does, it drags the shell around by a hook on its tail. When it gets bigger, it has to find a bigger shell. The crab in the photo is poking just its legs and antennae outside its shell. The shell is even shading the crab from the hot sun.

When the crab is frightened, it can hide inside the shell. Sometimes, if a predator grabs its shell, it will just leave the shell behind and run under a rock. Hermit crabs in areas with strong waves, though, always hold on to their shells so that they don't lose them when the waves crash.

Low Tide Alert!

Hermit crabs head to the bottom of the pool when the tide gets low. They also hide under rocks or even cluster with sea anemones to protect themselves.

Tip: Finding Hermit Crabs

Blue-handed hermit crabs like to visit California tide pools. They have blue "bracelets" on each leg, red antenna, and olive bodies. They are 0.75 inches long, or about the size of a quarter. You will see them running sideways, holding their claws up, on rocks.

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Designed and written by Sherry Weaver Smith, last modified 3/2002.