7 things you never knew about the hermit crab

1. House bound

These soft-bodied crustaceans are so dependent on their shells for protection that they will only venture out to copulate or to upgrade to better accommodation.

2. Paddling pools

Only smaller specimens, inhabiting periwinkle shells, tend to occur in rockpools. Larger ones, which can reach 8cm in length and require more spacious accommodation such a whelk shells, usually live below the low-tide mark.

3. Identity crisis

Hermit crabs are not true crabs, from which they split about 200 million years ago, but are more closely related to squat lobsters, which are not themselves true lobsters.

4. Multipurpose mouthparts

These opportunistic omnivores will scavenge, kill, browse and graze whatever plant or animal matter is available. They are readily cannibalistic and can filter microscopic food from the water using their bristly mouthparts.

5. Multiple occupancy

Common hermits encourage anemones to attach to their shell, and will even transfer them from shell to shell when they move house. The anemones' stinging tentacles may deter predators.

6. Handed hermits

Unlike many fiddler crabs, which may be left- or right-handed, a common hermit's right-hand claw, or cheliped, is always the larger of the two.

7. Growing smaller

If they find themselves in a shell that is too small, and if nothing larger is available, common hermits have the rare ability to decrease in size from moult to moult.