Species of interest blue crab American oyster horseshoe crab hard clam fiddler crab mantis shrimp Atlantic oyster drill hermit crab Atlantic ribbed musselblack-fingered mud crab
	carapace scavenger

Background

The hermit crabs that live in the coastal waters and along the shores of the Chesapeake Bay and the mid-Atlantic coast are crustaceans belonging to the family Paguridae. Hermit crabs use a borrowed shell (they're also called "robber crabs") to protect their abdomens, which lack an exoskeleton. Although there are a few terrestrial species, such as the land hermit crab (Coenobita clypeatus, in the same family as the coconut crab), which lives above the high-tide line from southern Florida to the West Indies, most of the approximately 500 species of hermit crabs are marine invertebrates that spend their lives in the littoral zone. Like many other crab species, they are omnivorous and will consume plant and animal detritus as well as live benthic organisms.

Photo: A long-clawed hermit crab (Parugus longicarpus) comes out of its shell.

Hermit crabs have five pairs of appendages, two pairs of antennae and a pair of mandibles or jaws, on either side of their mouth, and two pairs of maxillae or mouthparts. Unlike its relative, the blue crab, the hermit crab has no carapace and must force its vulnerable, asymmetrical body into the curved chamber of an empty mollusk shell for protection. The crab twists to accommodate the shell's whorls; once inside, its abdominal appendages help it to support the shell on its body. In water the shell's weight is reduced, which gives the crab greater mobility than it has on land. When threatened the hermit crab withdraws deep into its shell, using its large pincer claw (or cheliped) to challenge predators. When a crab has outgrown its shell it searches for a larger one, and if the new shell is not empty will use its pincer to remove the inhabitant. Then it cautiously abandons the outgrown shell for the new.

Hermit crabs appear solitary, but they do not always live alone. Polyp colonies may develop on the surface of its shell, to the organisms' mutual advantage: the polyps consume the crab's leftovers, while the polyps' stinging cells offer the crab extra defense against predators. Occasionally a hermit will take on a larger hitchhiker, such as an anemone or sponge, which gives the crab greater camouflage; when it's outgrown its shell, a hermit may even remove the useful organism from the old shell and bring it along to its new, larger one.

Several marine hermit crab species can be found in the Chesapeake Bay region. The most common is the long-clawed hermit, Pagurus longicarpus, which lives in snail shells and grows to about ½ inch in length and 3/8th of an inch wide.

Photo: A long-clawed hermit crab (Parugus longicarpus) on sea lettuce, in a shell covered by a hydriod colony.

Pagurus longicarpus inhabits the shorelines and muddy or sandy bottoms of the Bay, in bay grass beds, from the low-tide line to waters as deep as 150 feet. Its body is greenish-white or gray, and its pincers are often gray with a light brown stripe. The right pincer is larger than the left and is three times longer than it is wide. The long-clawed hermit lives in oyster drill shells, periwinkles or mud snails, and its native range extends from Nova Scotia to Florida.

The larger, flat-clawed hermit crab, Pagurus pollicaris, also lives in snail shells and reaches an adult size of 1¼ inches long and 1 inch wide. Its body is gray or white, its eyestalks brown, and its claw "hand" is broad, about 2/3 of an inch wide. The flat-clawed hermit can be found from Cape Cod to Florida and as far west as Texas, and lives on sandy bottoms and the Bay's shorelines from the low-tide line to water 150 feet deep. The flat-claw moves into the shells of moon snails or those of larger whelks.

Pagurus acadianus, the Acadian hermit crab, grows to roughly the same adult size as the flat-clawed hermit and also lives in snail shells, but has darker coloration-usually a brownish body with reddish-orange appendages. Its pincer has an orange or red stripe down the middle; its eyestalks and antennae are blue and its eyes yellow. The Acadian hermit can be found as far north as Labrador and south to the Chesapeake Bay. It prefers rocky tide pools at the northern part of its range, and waters as deep as 1,600 feet in the southern areas.

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Last modified: 12/11/03