When you find a snail shell at the beach or on a dive, you really must leave it alone. You may think that it is empty when in reality it may have a hermit crab hiding deep inside or else it could soon become the home of a hermit crab. Fishermen smash snail shells to use the snail for bait. Our hermit crab populations above and underwater are suffering from a severe drop in shell availability and that limits their ability to survive.

What is a hermit crab? 

 A hermit crab is not actually a crab, but a close enough relative that we won’t quibble about it here. Crustaceans (including lobster, shrimp and true crabs) do not have an internal skeleton. Instead they are covered with a chitinous exoskeleton. When a crustacean gets too large for their exoskeleton, they moult by crawling out of it and then quickly swelling up with water. A new shell forms rapidly over their enlarged body and they can then spend many months growing normally, replacing the water with body tissue until it is time to moult again.

 But unlike all other crustaceans, the hermit crab has a soft, unprotected abdomen that is specially adapted to holding on to a thick protective snail shell or anything else that will serve the purpose. Under the camouflage of the snail shell, they can go out on the reef in the daytime and forage for anything they can find including algae, plankton, worms, small fish and dead organisms.

 Furthermore, a hermit crab is not a hermit. They often live in large groups so that they can enjoy the hand-me-down shells of each crab as they all grow and need a larger one. If the largest crab cannot find a bigger shell, his growth will stop and he will likely have trouble surviving. Younger ones will fight him for the shell and leave him homeless and vulnerable to attack. Hermit crabs spend a lot of time hunting for a new shell and use the smell of a dying snail to help them locate one.

 As a graduate student of marine biology, I studied the way a hermit crab fought for a better shell. It is quite a noisy affair as the attacker gets a good grip on the defender and grinds and beats one shell against the other. He may pull the other crab out of the shell, or the crab may come out quickly on his own. The first crab feels around inside the empty shell, and then, keeping a grip on both shells he quickly pulls out of the old and backs into the new one. He sometimes does this several times as the shell-less crab waits impatiently to get into whatever shell is left over.

How do you photograph them? 

 They are the best animals on the reef to photograph although most divers totally overlook them. If you see a snail shell on the bottom, touch it gently. If it sticks to the bottom, it is a living snail and you must leave it alone. If the shell is occupied by a hermit crab, you can pick them up easily without hurting them. Make a careful note of where you found it because you must put it back exactly where he was.

 Find a nice setting that allows you to get the camera a little lower than he is. Stay away from corals or green sea mat as these are too fragile and may be hurt by the crab’s shell. Choose the base of a sea fan or a hardy sponge. Place the crab so that the opening is almost toward you, but not entirely on its back. If he is slow at coming out, tilt it more downward. Once he comes out, he may move quickly, so you must shoot as soon as you see his beautiful eyes and legs.

 After your photos, say thank you to him and put him back where you got him.

Why do we need hermit crabs? 

 I need them because they are downright cute! And, like all creatures, hermit crabs add to the stability of their natural environment. They help to keep the reef clean of dead organisms and algae and they serve as food to other animals including nurse sharks, fish, squid and octopus.

Don’t take the snail shell 

 If divers frequently pick up empty shells, or beachcombers pick up whole snail shells then there will not be enough available for the hermit crab population. It has become a truly limiting factor in areas where shells are collected both legally and illegally. Anyone who buys products made with snail shells is possibly robbing a hermit crab of a proper home. If you find one on a beach, you know that if you leave it there, someone else will just take it anyway. What should you do? I would take it and throw it further into the water, or perhaps hide it above water near areas where there are hermit crabs. I have taken shells and written on them that they are for the hermit crabs and taken them down to my favourite dive sites.

 I have seen a sharp decline in the numbers of several species of hermit crabs, and we all need to work hard to turn that trend around.

Enjoy the journey,
Cathy

For more information,
contact Cathy Church’s Photo Centre on 949-7415.
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