Mobile homes
By Nichole van Beek and Hermit Crab(s)

Started on: 06/06/06 14:12:59
Medium: Visual

Hermit crabs find new homes when their old ones become too small and cramped. Could I fabricate a home that would be an acceptable alternate to a shell? Some accounts on the internet have described finding hermit crabs in film canister or medicine bottle homes (I have not been able to find any images). With a shortage of acceptable shell homes it seems likely that a hermit crab would take on one that I build. suggests that the home be light, protect from predators, have a circular opening, and a smooth interior. Although we are nearing the end of the class, this is something that I will certainly consider for the future. Since I have no interest in owning and maintaining hermit crabs, I would consider leaving my homes in the wild for hermit crabs to find.

The following information is taken from

"Obviously the crab wouldn't wear a shell if it had one of its own! The rear part [of the crab} (the abdomen) is very soft. The abdomen is arguably the most important part of the crab's body, because it holds the crabs digestive glands and reproductive system.

But why a sea shell? Common sense tells us that the sea shell affords the hermit crab complete mobility AND security from predators. The perfect hermit crab shell has no holes, and fits the crab snugly, but allows him or her to withdraw into the shell completely.

Oddly enough, when hermit crabs first crawl ashore as juveniles, the shape of the 'shell' they find will influence the growth of their abdomen. For example, if a crab comes ashore and only finds a bamboo tube in which to tuck its' rear, the crab's abdomen will not develop the traditional curl to the right, but will remain straight. One would like to think that there are enough shells available in the natural environment for the hermit crabs, but this is not always true. Hermit crabs have been found 'wearing' plastic bottle tops and airline liquor bottles.

Another very important purpose of the crabs shell is to minimize the evaporation of water from the crab's body...moisture is the most important thing in a hermit crab's life. Everything about their life cycle, aside from their mating ritual, revolves around conserving moisture -- the crabs are not active during the heat of the day to conserve moisture; the crabs are out and active during rain falls so they can experience the maximum effect of the rain. So you can see why a properly-fitting shell is so important to the crab. A crab in a durable shell with a snug fit and access to adequate water lives much longer than a crab in an ill-fitting shell.

[The] crab should be able to completely withdraw into its shell and seal the opening with its large pincher. Some crabs like shells a little larger or a bit smaller, but as long as the shell covers the abdomen closely and completely, there is no real reason to fret over your crab being in a shell that is too small. The same goes for a crab in a shell that you think is too large. If the crab is able to maneuver the shell while it is walking, there is no need for you to worry that the shell is too large.

Take your crab in your hand and look at his large claw. The perfect-fitting shell will have an opening about the size of the large claw plus about 1/8" all around (for larger crabs it will be more) or 1/10" all around. You're ultimately looking for a shell whose entrance the crab will be able to plug with his or her large claw and far left walking leg.

Measuring the Aperture (Opening) A method sea shell collectors often use to judge the size of a shell is by its aperture or opening. Take the shell and put a ruler across the mouth of it and there you have it! Small crabs require a shell with an aperture of 1/4", larger crabs with 1 1/2" to 2" and up. If you're trying to buy your crab a shell that will fit better than the one he is in, take a rough estimate of the aperture of the shell he's occupying, and guess-timate the proper size. A good sea shell shop will accept a shell if it is returned in new condition, so you have nothing to lose if you fail to order the correct size.

The best shell for your crab is one that he chooses, no matter if you think it is pretty or not. To be blunt, it is not your abdomen in that shell so if you provide him with a beautiful shell Good Purple Claw crab shellwith a dirty interior or holes, the crab will not want it! Provide...crabs with clean shells. All shells...should be boiled on the stove at a rolling boil for about five minutes, the allowed to cool. If you have an especially beautiful shell that you're excited about giving to the crab as soon as possible, you can boil it, and then after the required five minutes, gradually pour off the boiled water while you pour cold water into the pot. This will cool down the water (and thus the shell) faster so you can give it to your crab.

Also, crabs are drawn to shells with circular openings (an exception to this is the Ecuadorian crab. This will be discussed later on). For some mysterious reason, hermit crabs are drawn to shells lined with mother-of-pearl. It is suspected that they like these types of shells because (1) mother-of-pearl is an excellent insulation from the environment, and (2) mother-of-pearl is very smooth and 'comfortable' on a crab's abdomen. Most crabs find a shell of the correct size, with no holes and a smooth mother-of-pearl interior hard to resist!"
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