The Hermit Crab

A student web page designed by: Ellie Halcrow

Phylum: Arthropoda
Sub-phylum: Crustacea
Order: Decapoda
Infraorder: Anomura
Family: Paguridae

Hermit crabs, the tidepool entertainers, are abundant around the world among both intertidal and subtidal critters. Their soft, unprotected abdomens are asymmetrical and curved to fit the spiral shape of snail shells they live in. Hermit crabs carry their shell homes on their backs and tuck themselves away inside for protection using their strong stomach muscles. They have two sets of legs that they extend outside their shell for walking and two pairs of legs tucked away inside that they use to move their body around inside their shell. Hermit crabs are "right-handed" as their right claws are larger and usually a different shape from their left claws. They use the large right claw for protection and holding food, and the small left claw for eating.

Hermit crabs hardly ever leave their shell, but when their home gets too small they go searching for a new one. Fewer empty shells in the tidal zone means fewer homes for hermit crabs. Even when this happens though, hermit crabs will never take healthy snails out of their shells, but they are certainly good at smelling out stinky dying or dead snails in hopes of a new home. This is not to say though that an aggressive hermit crab won't go for a good looking shell already occupied by a more shy hermit. In this picture you can see the dominant crab on the right attempting to pull the more submissive crab on the left out of his cozy shell. Most hermit crabs like to live in snail shells, however, there are some hermits that cover themselves instead with sponges for protection. Steven's hermit (Pagurus stevensae) is one type of hermit that lives wrapped up in a sponge.

Male hermits are often seen dragging around a female by their small claw, fiercely fighting off rival suitors with their big claw. The male will drag his potential mate around until she is ready to molt. When the female crab molts she is receptive and the male can then fertilize her eggs.

Hermit crabs are mainly scavengers and can often be seen digging for food, preying on smaller organisms, or scrounging for scraps on the ocean floor.

Here are 4 distinct types of Hermit Crabs found along the coast of B.C.:

BLACK-EYED HERMIT (Pagurus armatus)

one of the largest hermit crabs
easily found in the Puget Sound area
loves Moon shells for homes

- large erect oval black eyes
- top surface of claws covered with spines
- legs and claws are banded in red, orange and white

- carapace length up to 43mm or (1.7in)

- Alaska to Southern California

- sandy bottoms in sheltered areas
- low intertidal down to 146m
- often found with seapens up to 479 ft down

HAIRY HERMIT (Pagurus hirsutiusculus)

the most common hermit crab in Puget Sound
lives in light-weight shell as it likes to move around a lot
if handled it may abandon its shell

- green to olive
- distinctive white band on the outer segment of the walking legs
- juveniles have more bright white stripes than adult animals

- up to 19mm (0.7 in)

- BC to Southern California

- upper and middle intertidal (rarely subtidal down to 110m (360ft)

GRAINYHAND HERMIT (Pagurus granosimanus)

like roomy houses into which they can completely withdraw, because they can move around so much in them the houses they choose seem like a heavy burden
can be act aggressively, attacking other hermit crabs for their larger shells

- uniform dark olive green with white or blue granules on the surface of the claws
- antennae are orange with no bands

- carapace length 19mm (0.7in)

- common in mid-low intertidal pools and under rocky ledges

THE TOOTHSHELL HERMIT (Orthopagurus minimus)

likes to live in tooth shells or worm tubes, seldom found in snail shells
for this reason these hermits have straight abdomens and an unusual shape
typically holds its large claw straight out in front for protection

- found living in worm tubes
- the right claw is flattened and much larger and redder than the left claw with cutting teeth along its edge

- small, carapace length just reaching 9mm (0.3in)

- found in intertidal waters along the BC coast down to Southern California

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