Hermit crabs can share their homes with all sorts of lodgers. Anemones that attach to the outside of the shell pay their way by providing protection; some even build an extension and free the crab from needing to move home. The ragworm, which lives in the shell alongside the hermit and grabs food from its jaws, is probably less welcome.

Only the front part of a hermit crab is protected by the usual crustacean armour. Its soft abdomen is coiled so that it fits neatly into the shells left by snail-like molluscs such as winkles and whelks. The shell is carried around everywhere, its weight being supported by the crabs hind-most legs.

When threatened, hermit crabs withdraw into their shell and use their claws as a barrier across the entrance. This works against most predators but not those, such as large crabs, which are equipped to break into the shell. Hermits are sometimes found living in badly damaged shells; they survived an attack or simply inherited the sub-standard home.

As hermits grow, they have to move into larger shells. Such changes involve lengthy inspection of the new home, with much poking, prodding and feeling about within the selected shells interior. They must also keep a watchful eye out for enemies, before finally whipping their rear from one shell to the next.

A male hermit crab will court a mate by tapping her claws with his, and the female responds with stroking movements of her claws and legs. Its not all gentility, however, and females are often seen being dragged unceremoniously across the seabed prior to mating.

The easy-to-please hermit can prey on live animals, scavenge for carrion, scoop up organic deposits or filter-feed on suspended material. In addition to gathering food, its versatile claws are used to signal submission or threat to other hermit crabs.