Common Hermit Crab

In Britain, small hermit crabs are a common feature of the shore, where they frequently adopt the shells of edible periwinkles (Littorina littorea), flat periwinkles (Littorina obtusata) and dog whelks (Nucella lapidus). In deeper water, the shells of the whelk (Buccinum) are often occupied. Occasionally, if two hermit crabs meet, one will attempt to 'steal' the other's shell by forcibly evicting the current owner. The common hermit crab is an omnivorous scavenger, and can also obtain food by filtering organic particles from the water (4). Reproductive activity tends to peak in January and February in populations dwelling on the shore, but in those living in deeper water, females have been found carrying eggs throughout the year (4). The female carries the eggs for around two months, after which time the pelagic larvae persist for a number of weeks. Maturity is typically reached before one year of age (4). A number of animals are associated with this hermit crab, particularly the sea anemone Calliactis parasitica, which lives on the shell of the hermit crab, and provides increased protection against predators, receiving improved food collection in return (4). This is known as a symbiotic relationship, as both parties benefit from the association (4). A parasitic barnacle (Peltogaster paguri) is often seen under the abdomen of the hermit crab as a yellowish mass, which is often confused with the crab's eggs (4).

Specific conservation action has not been targeted at this species.

Despite the common name, hermit crabs are related more closely to lobsters than to crabs. They lack a hard carapace, and adopt the empty shells of gastropod molluscs (such as whelks), carrying them around and swapping them for a larger shell as they grow (3). When seen out of a shell, hermit crabs have a bizarre appearance; the soft abdomen is twisted, which allows it to fit into the coils of the gastropod shell (4). The common hermit crab is typically reddish or brownish in colour, and has two pincers on the first pair of walking legs. The right pincer is larger than the left, and both have a rough, granular surface (4).

Inhabits both rocky and sandy areas from the shore to depths of 140m (4).

Common and widespread in north-west Europe, and found around all of the coasts of Britain (2).

Common and widespread (2).

Not currently threatened.

In Great Britain and/or Ireland:
Animal / parasite / ectoparasite
Athelges paguri ectoparasitises gill chamber of Pagurus bernhardus
Other: unusual host/prey

Animal / parasite / endoparasite
adult of Peltogaster paguri endoparasitises body of Pagurus bernhardus

Animal / parasite / ectoparasite
Pseudione hyndmanii ectoparasitises branchial cavity of Pagurus bernhardus

Animal / parasite / ectoparasite
Pseudione proxima ectoparasitises branchial cavity of Pagurus bernhardus

Hermit crabs have a 'naked' hind body. Only their front end is covered with shell. In order to protect their naked hind end from hungry animals, they hide this part in empty snail shells. The entire back end disappears in the shell; only the head, the legs and the sturdy pincers stick out of the opening. As opposed to the small hermit crab, the right claw of the common hermit crab is larger than the left claw. Because hermit crabs grow but their protective shell doesn't, they must regularly move into large snail shells. Smaller hermit crabs can be found in periwinkles. Larger ones are often found in whelks. Sometimes, you find the shells covered with a rough substance. Although it looks like algae growth, it is the animal polyp sea mat.

There are around 1100 species of hermit crab. Unlike their lobster relatives, most hermit crabs lack a hard shell. Instead, they have a soft, curved body. To protect themselves, most find empty seashells to live in. Hermit crabs will sometimes fight over a new shell. The common hermit crab lives along the Atlantic coast of Europe.

Pagurus bernhardus is the common marine hermit crab of Europe's Atlantic coasts. It is sometimes referred to as the common hermit crab or soldier crab. Its carapace reaches 3.5 centimetres (1.4 in) long, and is found in both rocky and sandy areas, from the Arctic waters of Iceland, Svalbard and Russia as far south as southern Portugal, but its range does not extend as far as the Mediterranean Sea. It can be found in pools on the upper shore and at the mean tide level down to a depth of approximately 140 metres (460 ft), with smaller specimens generally found in rock pools around the middle shore and lower shore regions, with larger individuals at depth. P. bernhardus is an omnivorous detritivore that opportunistically scavenges for carrion, and which can also filter feed when necessary.

Illustration by Augusta Foote Arnold.

Pagurus bernhardus uses shells of a number of gastropod species for protection, including Littorina littorea, Littorina obtusata, Nassarius reticulatus, Gibbula umbilicalis, Nucella lapillus and Buccinum. In the warmer parts of its range, the sea anemone Calliactis parasitica is often found growing on the shell occupied by Pagurus bernhardus. In colder waters, this role is filled by Hormathia digitata. Hermit crabs fight one another for gastropod shells and have a preference for shells of certain species.

Eats on dead organic material. A long foreplay, to ensure the baring of the abdomen was not vain. The mating only lasts less than a minute.

In the intertidal area and beneath. On rocky shores, shell bottoms and sandy and silty sediments, but never muddy. Among vegetation, as seagrass beds. Adults in shell of whelk, juveniles on beaches, often in shell of (peri)winkle and moonshells

Largest and most common heremit crab in our region. An average length of 10 cm, carapace of 3,5 cm. Color: red-orange. Only two out of four legs well developed. Only one cheliped, or scissor (almost always the right one) is much bigger. The pair of scissors always bear length ridges with a row of knobs on top. Eyes positioned on a stalk.