Hermit crab Pagurus bernhardus

Hermit crabs are crustaceans, i.e., they are related to crabs, lobsters and prawns. However, unlike other crab species, hermit crabs do not have their own carapace or shell. Hermit crabs have a soft, vulnerable abdomen and occupy empty seashells to protect themselves and from which they derive their name ‘hermit’. They are usually a reddish-orange colour.

Behaviour

The hermit crab will crawl around with the shell on its back and will only leave when it grows too big, and has to find a new, larger shell, such as that of the common whelk. In most cases, they will use the shells of dead snails, but squabbles for possession of an already occupied shell frequently occur. In addition to finding a new ‘home’, hermit crabs also moult. When ready to moult, the new skeleton grows under the old one. The old exo-skeleton splits and comes off; the new skeleton takes some time to harden.

One of the most fascinating aspects of hermit crab behaviour is their association with other animals. Acorn barnacles, or algae can be found growing on their shells and they can enjoy symbiotic (mutually beneficial) relationships with sea anemones. The anemones’ stinging tentacles help to deter predators and provide amazing camouflage. In return, the sea anemone gets scraps from the Hermit Crab’s meals and is transported to food sources. Some hermit crabs even transfer their anemones when they ‘move’ from a smaller shell into a larger shell. Like all British crab species the hermit crab is a scavenger and will look for dead and dying forms of marine life to feed on.

Size

  • Length: commonly around 1-4cm
  • Weight:  200-500g
  • Average Lifespan: 1-10 years

Status

Common. Not threatened.

Distribution

Hermit crabs are native to the UK and found across the whole of the British Isles. The common hermit crab is found everywhere in the North Sea.

When to see

The best time is at low tide, after a storm, when hermit crabs have been dislodged from their home. Juvenile hermit crabs are common on rocky shores in all months of the year.

Facts

  • There are around fifteen species of hermit crab found in the UK; the most widespread and largest being the aptly-named common hermit crab (Pagurus bernhardus).
  • Hermit crabs of the ‘Paguridae’ family are right-handed hermit crabs, e., the right claw/pincer is the largest and used to close off the aperture of the shell when the crab is threatened.
  • Despite their name, hermit crabs are not solitary creatures. They live in large colonies of 100 or more, where they often sleep piled up together and can even collaborate in teams to find food.

Common name

Hermit crab

Species name

Pagurus bernhardus

IUCN Red List status

N/a

When to see in Scotland

The best time is at low tide, after a storm, when hermit crabs have been dislodged from their home. Juvenile hermit crabs are common on rocky shores in all months of the year.

Where to see in Scotland

Scottish Wildlife Trust reserves such as Handa Island and Ballachuan Hazelwood.

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