The Land Hermit Crab uses a shell to protect its delicate body. The shell is sometimes that of a land snail when the crab is young, but usually that of a marine snail (whelks). Once deceased, the snail's body decomposes and the empty shell eventually washes onto shore. The Hermit Crab can then occupy the shell. Larger shells are necessary as the crab grows, but that growth is quite slowly.
Hermit crabs are very particular about their shells and shell switching is not uncommon as the crab searches for the perfect shell. A desired characteristic of that shell is an opening about the size of the large claw, plus about 2 1/2 - 3mm (1/10 in to 1/8 in) all around (more for larer crabs). When threatened, the crab withdraws into the shell and blocks the entrance with the large claw.
Fierce shell fights can occur if the shell supply is not adequate. The loser often dies since many hermit crabs will not release their grip on their shell until they are torn apart. The loss of limbs in shell fights is common, but may not result in death especially since the hermit crab can choose to drop a limb to disengage from from the conflict.
This crab is called 'The Soldier Crab' in the Cayman Islands. There delicate bodies (gut) are mainly used as bait for fishing. The remaining parts, claws and shell, are smashed and thrown into the sea for 'scent', which is a way of attracting fish to your desired location. These crabs are plentiful in Little Cayman as they are fed daily by the locals. They will eat 'left-overs' (rice, bread, meat, vegetables etc...) If they are stored in a bucket, a cover must be placed, slightly open for ventilation, because these crabs work together to climb on top one another as a way of escape.
