Why Hermit Crabs Leave Their Shells

Hermit crabs are nice little pets that can live for up to 20 years with you if you take care of them properly. They might not learn to speak or play fetch, but they are fascinating little creatures on their own. They are very active, investigating every corner of their habitat, burrowing in the sand, and crawling on top of the rocks constantly.

Despite the name, they are actually quite social beings, and will even stack on top of each other if they are living together in larger groups, which is when they are the happiest. Hermit crabs are recognisable by their shells, and it is quite interesting that the shells are almost the currency in their world. Some crabs exchange shells with each other, and the other will fight aggressively for a shell they want.

Their shells are their homes and their protection. When crabs feel like they are in danger, they retreat into their shells immediately, as they do not really have other ways of protecting themselves. They do have claws (the right one is used for defense and the left one for collecting food and water), but without the shell, it is not enough. Hermit crabs are omnivores, so you can experiment with different kinds of food to find the one your crabs will like the most. They are sensitive tiny animals, but they can be very rewarding pets, as there are sociable, active, and highly inquisitive.

Despite their small size, and the fact they probably look easy enough to look after, they require a great deal of maintenance, and something can easily go ‘wrong’. For example, they might suddenly start leaving their shells and refusing to return into it. The problem is, when hermit crabs leave their shells, they become exposed to the outside (especially their soft abdomen), and they start being at risk of drying out or being hurt by other crabs. So what to do in that case to prevent the crab from being injured, and how to get it back into a shell?

First, let’s talk about potential causes of a hermit crab leaving its shell. Because it borrows snail shells to live in, it simply might be that it has grown too big for its current shell and it needs a new one. And/or it might be pre-molting because it is about to shed its exoskeleton. If that is the case, you might be able to recognise it by several tell-tale signs (although not all of the crabs will display all, or sometimes any at all, symptoms).

• It has been gorging on food for about two weeks and then suddenly stopped eating altogether.
• It appears lethargic.
• It’s body and legs have turned lighter in colour, becoming beige-like.
• It drags its shell or a big claw as if it is too heavy for it.
• It acts restless during the day, trying to climb out of the habitat.
• It spends lots of time in, or around, the water ponds, both freshwater and ocean ones.
• It goes into almost hiding from the other crabs (you could say it starts behaving like... a hermit)
• It becomes uncomfortable with the shell it is wearing, changing shells a lot but being dissatisfied with all of them.
• Its eyes seem to appear facing outward.

If you notice these signs, and your crab’s habitat is otherwise impeccable, you do not need to worry and can just leave the crab to do its thing. However, after the molting, the crab will want to move in a bigger shell, so make sure it has several choices of shells readily available for it to choose from.

When a crab leaves its shell, and it is not because of the molting or the size issue, that means that it is under some sort of stress, or that there is a problem with its shell.

There are several common issues that can cause this to happen:

• The shell your crab is currently using might be irritating it for some reason. There might be sand, mites, fungus (a bacterial or fungal infection might be causing your crab a skin disease), or other foreign objects lodged inside of it, and hermit crabs are also known to hide their food inside of their shell. This problem is sometimes remedied by crab itself by molting. If not, you can boil the shell in dechlorinated water and shake it vigorously until whatever is in there gets dislodged. It should work most of the times.
• There is another crab in its shell. Hermit crabs sometimes leave their shells to try out other ones for fun. However, if you have multiple crabs in one enclosure, while one is out of its shell, another one might slip in and take its place. Hermit crabs sometimes even fight about the shells they feel are desirable. Those fights can be even to death, as a crab would often rather die than give up its shell. To prevent this, there should always be an ample selection of shells of various sizes and ‘styles’ in the habitat, so every crab can find something that suits them.
• A hermit crab might also leave its habitat if the temperature or humidity of their habitat is too high or too low. The ideal humidity for these crabs is 70-80 percent, and the warmth should be of various sizes in different ends of the habitat, ranging from 72-75F to 80-82F.
• Your crab might be under the physical stress too. Before they reach the pet stores, the conditions in which they are harvested and transported are quite inhumane and make them suffer. To add to that, when they come to the stores, hungry, dehydrated, and stressed out, the employees often do not know how to care for them. So when you buy the crabs, they might be in bad health already, to put it that way.

So, your crab is out of its shell and it will not go back in. What can you do to help coax it back in?
The first method described is used for the situations in which a crab has left its shell for reasons other than molting. In the case of molting, the procedure is different (and it will be described too).

Before and after handling the crab and its shell, wash your hands thoroughly. The best way to start is to rinse or boil the abandoned shell and shake it thoroughly, as mentioned before, so that anything that might not belong in there gets removed. Pour out most of the water from the shell and place it in a cup or a bowl, depending on the size of the crab. You can also mist the shell with the dechlorinated sea saltwater. The container in which you put the shell in should be just big enough for the crab and the shell, not bigger, and, of course, not too small either. Add some dechlorinated sea salt water into the bowl to prevent the crab from drying out and dehydrating.
Take the crab carefully from its enclosure by lightly holding it just behind the last pair of walking legs, or use a spoon to gently scoop it up. Put it for three seconds in a bath of lukewarm saltwater. Examine its abdomen carefully for any signs of irritation or injury and be very careful that it does not try to escape, as it can injure itself a lot that way. Check it out for the molting symptoms too, such as the lifting of the old exoskeleton, transparent eyes, etc.

Put the crab into the bowl next to the shell and cover the bowl and leave it somewhere dark, but with the appropriate humidity and temperature. You can put the bowl back into the enclosure, but make sure that other crabs cannot climb in it. You can make it dark in there by covering the bowl, but, of course, make sure it still has enough air available. You can use a washcloth or something similar. The darkness should help your crab relax and make it feel secure enough to get back into the shell. Quite often, an hour or so should be enough.

Another thing you can do is keep the crab and its shell in the habitat, but make an isolation zone by cutting up a large soda bottle in half, and then putting it so it surrounds the crab and the shell, with an open hole on top so that, once again, the crab does not lack air. If the crab takes longer to move into a shell, provide it with easy access to food and water too.

You can also give the crab multiple housing options to choose from. If you have noticed that it likes a particular shape or style of the house, place several of the similar shells around it, preferably a bit larger than the one it has been living in before. Clean them before putting them in and mist them with dechlorinated sea saltwater. If the crab is slow to enter a new home, there is not much more than you can do than just wait. Keep providing it with food and water and keep the correct heat and humidity for it. It should not take the crab a long time, unless it is molting, but if it does, one trick you can try is removing a few shells for a day or two and then returning them until the crab finally chooses one. To make sure that the crab does not dry out, you can add a drop of dechlorinated water to its abdomen hourly.

In the case of current or recent molting, handling the crab needs to be even more careful. You can use the cut bottle method, but be aware that, while it will prevent ‘threats’ from above, it will not stop the crab from burrowing in the ground, so if it goes deeper, it can exit the protective dome. If the other crabs seem to be a threat to the molting crab even after it is in the dome, you might have to remove it to a more secure container, such as a bowl with a lid (but poke holes for air in the lid), inside of the habitat. When you do it, make sure that there is at least six inches of the substrate so that the crab can burrow fully and complete the molt. The bowl should also be slightly larger than it is necessary for the non-molting crab.

When moving the crab into the isolation bowl, gently scoop it up with a spoon, but make sure you scoop the substrate below it too, so that the crab is not touching the spoon. Place the crab into a bowl carefully along with its most recent shell and a couple of similar ones. Do not add water to the bowl because of the crab’s soft exoskeleton. If the old exoskeleton is still available, be sure to put it in the bowl too. Add some water and different kinds of food for the crab. Some of the options are scrambled eggs, honey, worm castings, or anything else you know the crab likes. The molting takes about a month, so you should be patient with the situation, and keep providing the crab with everything it needs.

In case of your crab leaving its shell, the main thing is not to panic or worry immediately. In some cases, it might be a sign of something bad, but most likely, it is either molting or is simply inconvenienced in some way. You can help it by following these steps. Of course, if you think that there might be something wrong with your crab’s health, do not dismiss it and bring it to the veterinarian. After all, you and they know the crab and its health history the best and can figure out most easily what is going on with it.