Seaside Hermits

By George and Lory Frame • Photos by authors

A coastal housing shortage has hermit crabs scrambling for real estate.

At low tide we walked along the mud flat behind a sandy beach. Around us we saw hundreds of snails that were stranded high and dry, waiting for the rising tide. Just then a little shell scurried across a puddle. It was too fast to be a snail, and it seemed to move the way a crab does. “That’s odd,” Lory said. We looked closer and saw that it really was a crab—a hermit crab in a tiny snail shell.

Tiny hermit crabs scour the shoreline for shells to call home. But good shells are hard to find, and many hermits are left unprotected.

Lory picked it up for a better look. The little crab snuggled backward until it was deep inside the snail shell. Only its broad claws showed at the entrance, blocking the passageway like a heavy gate in front of a castle. These little crabs are called “hermits” because of the way they live alone, not allowing anybody else inside.

Hermit crabs are specialized for living in shells that they find. Their long, thin, soft abdomen curls around inside the spiral of the shell. They hold on for dear life, because without their borrowed shell they would make a soft meal for birds and predatory fishes. We never tried to pull a hermit out of its home, though, because it would let itself be pulled apart rather than let go.

We wanted to learn more about these curious little crabs, so we watched them for several weeks one summer on the New Jersey coast. At low tide, when the water was only a few inches deep, we waded in the warm, shallow water to look for hermit crabs.

Out on the mud flats there weren’t enough empty shells of the right size for all the hermit crabs that needed them. Some tried to squeeze into shells that were much too small, and of course they hung out even when they tried to hide. Gulls and other birds ate many of these unlucky ones.

As hermit crabs grow bigger, they outgrow their shells. To get a better shell, hermits have “shell fights” with one another. When hermit crabs notice a snail being eaten by a predator, they gather around. They wait to “inherit” the empty shell, because there is always a shortage of shells that are the right size. And while they’re waiting, they fight to see which will actually be the one to get the shell. Usually the biggest hermit wins.

We wanted to get an even closer look at hermit crab behavior. We collected several hermits and put them in an aquarium full of seawater. Then we gathered together an assortment of shells from our collection and dumped them into the aquarium to see what would happen.

A hermit crab explores a new shell. Hermits are glad to find an empty shell, even if it’s too small.

The hermits didn’t waste any time checking out the empty shells. It was almost like a game of musical chairs, with several hermits exchanging shells at the same time. They were so quick, they moved out of their old shells and into the new ones in hardly more than a blink of an eye.

One especially large hermit (about two inches long), which we named Edgar, was a real go-getter. He constantly ran around, tapping on everybody else’s shell. Maybe his own shell was too tight, and he was looking for something roomier.

One afternoon he met Walter, a smaller crab whose shell was much too big. When Walter and Edgar met each other, they felt each other’s houses and seemed to come to an agreement. They switched houses, and afterward both seemed much more comfortable. This kind of “friendly” exchange of shells goes on quite frequently.

We enjoyed watching our lively little hermit crabs, but we had to let them go at last. We carried them down to the shallows beneath the pier and gently lowered each of our houseguests back into the water.

When we got back to the house, Lory looked ruefully at our depleted shell collection. Some of the shells had been very pretty indeed, but the hermit crabs needed them. We decided to dump the last of our shells into the water for the hermit crabs. After all, it was fun to have lots of these little critters around.