Ocracoke nature, flora & fauna

Spotted On Ocracoke: The Hermit Crab

Hermit crab IMG_8158

 

June 2011

Text and Photo by Peter Vankevich

I think this month’s feature is one of the more fascinat­ing creatures one may find on Ocracoke. Hermit crabs are decapod crustaceans, that is they have ten legs. Their shape is elongated and asym­metrical. Because they lack an exoskeleton (hard shell) to protect their body, especially the abdomen, they will use seashells or if they are un­available other hollow objects for protection forcing their pliable body inside such as one would use a sleeping bag. The variety of univalve shells they use is vast including periwinkles, augers, moon snail shells and even the large whelks.

They get the name “hermit” apparently due to their not having a permanent home, i.e. shell, and having a repu­tation as being solitary. More on that in a moment.

Worldwide there are about 1100 species, most found in coastal and shallow muddy waters. A few are considered to be terrestrial preferring muddy or sandy areas usual­ly within a few hundred yards from the shore. On Ocracoke where there are about four species, you may come across them during the day, but they are most active in the early evening and nights when there are fewer predators around. A good spot I have seen them during the day is in the shallow warm waters at Springer’s Point.

As you will note from the photo, barnacles and many other living organisms will live on the outside shell. They are omnivorous scavengers, feeding on vegetal matter as well as dead fish and living plankton.

A suitably sized shell will permit a hermit crab to with­draw completely if a preda­tor attempts to harm it. As they outgrow the shell, they must seek another larger one. If they cannot find an empty shell, they may force another hermit crab out by using its strong pincers or by violently rocking the shell. Rarely, they will attack a living mollusk. Recent research has shown another more sophisticated strategy in the quest to obtain “better housing.”

Whereas we humans are greatly consumed with so­cial media these days, a study published in 2010 by biolo­gists at Tufts University re­veals that hermit crabs may locate new and better suited shells using previously un­known social networking skills. Contrary to their name and previous solitude-loving reputation, hermit crabs often find the best new shells when they work together. When a large shell becomes available, crabs may gather around it and queue up in a line from the largest to smallest. Once the largest crab moves into this vacant shell, each crab in the queue swiftly switches into the newly vacated shell right in front of them. As a result, a single vacant shell kicks off an entire chain of shell vacancies that ultimate­ly leads to many crabs getting new, and generally more suit­able shells. This behavior has been named the synchronous vacancy chain.

Over at the Ocracoke Cof­fee shop one nice spring morning, I heard a good porch story. I’m not sure if it qualifies for a Rob Temple or Don Davis yarn to be recount­ed at Deep Water Theater or has some veracity. Anyway, a couple found some interest­ing seashells and took them back to the room they were staying in one of the older establishments. Placing them in a neat row on the dresser, they went out for a drink. Coming back, some of the shells had moved. Other than that, it didn’t appear that any­thing else was out of place. Strange place this island is, they thought. As midnight approached, they heard some noises and turned on the light. The shells were now on the floor and moving around. Ghosts! – they feared. As they watched a little more closely, they saw legs moving them around. Some of the shells they had picked up contained well-concealed hermit crabs and in the morning, it was time for a quick walk to the Springer’s Point for a release.

If you have any comments on this, or suggestions for a future “Spotted” column, feel free to contact me, pete­vankevich@gmail.com