Hermit Crabs rely heavily on a safe shell to use as their home; a shell will protect them from predators, injury to their abdomen and organs and keeps their soft abdomen moist and protected. Infact, a Hermit Crabs shell is so vitally important, that without it, they will die within a matter of days. Failure to find a shell, severely increases the chances of being attacked by predators, and having their soft abdomen dry out.
Land Hermit Crabs cannot make their own shell; therefore, they must take unused Gastropod shells. In the wild, Hermit Crabs will take whatever they can get, even if it is too big, too small, broken, contains holes or is infact not a shell at all. Because they know, without it, it is a death sentence.
In captivity, it is up to us to provide the correct type of shells in the right sizes so that your crabs have a good selection of well-fitting shells to choose from. At least 6 spare shells per crab, these can be placed directly on the substrate, in a bowl, on a second level or you can create a little shell shop style basket.
As long as the shells are accessible and suitable, your crabs will change when they are ready. With thousands of shells on offer, and loads of different openings, shapes and styles, it can be hard to know what to choose.
Openings include D Shape, O Shape, and Oval. These are the most common openings in Hermit Crab shells. Every crab will have their own preference, some prefer a D shaped shell, others prefer O shaped, and some prefer Oval. Its best to offer a variety of opening options so your crab can decide what they like best.
* O Shaped Opening - Turbo
* D Shaped Opening - Natica
* Oval Shaped Opening - Babylonia
Popular Shells for Australian Land Hermit Crabs
Land Snail Shells
Whale Eye Shells
Just to name a few, at the end of the day, only the crab can decide what they like best, it's up to us to make sure they have lots of options available.
Shells to Avoid
Painted shells Painted shells are covered in toxic paint, and when consumed, they can make a crab very sick. Always offer natural shells within your tank to avoid poisoning your hermit crabs. If your crab has already come in a painted shell, never try to remove them from their shell, or force them to take another shell, simply offer natural shells and they will change when they are ready. Once they change from their painted shell and have happily kept their new natural shell for 24 hours, remove the painted shell and bin it. Do not try to pick the paint off or clean the shell for reuse, the toxins from the paint have already absorbed into the shell and that shell is now unusable.
Broken shells Broken shells can pierce the soft abdomen and injure the crab, they also prevent water staying inside the shell and can cause the moist abdomen to dry out. Remove those shells and bin them.
Shells with holes Shells that have holes down the side or towards the end of the shell will leak shell water and make it harder for your crab to keep their much-needed shell water full. Remove those shells and bin them.
Spikey shells or very long shells Shells that are spikey or too long can make it hard for your crab to move around the tank, climb, get in and out of pools and dig or move into small spaces to hide.
Shells with the spiral going to the left hand side A Hermit Crabs abdomen naturally curls to the right, so all shells offered should also coil to the right for the crab to fit properly. (Their right, your left)
Plastic or glass shells Plastic and glass shells are not suitable for Hermit Crabs, they require real, natural shells, not man-made. Plastic and glass shells can break and shatter and seriously injure the crab.
How to measure your Hermit Crabs shell
Gently pick your Hermit Crab up by the shell and flip him over, he should retract back into his shell, this is the time to measure his opening to ensure you have the correct sizes available.
Using a digital caliper, ruler or tape measure, measure the opening of your crab's shell along the longest part, make sure to measure the inside opening of the shell, do not include the edges of the shell in your measurements.
When purchasing new shells, go up a size that is roughly 0.5-1cm bigger than their current size (if it fits) if they are too big for their current shell, you will need to go up a bit more to compensate for their size.
Examples of how to measure a shell are pictured below.
Boil all NEW shells (only shells that have never been in your tank before) in primed water for 10 minutes.
Remove from boiling water and place onto a towel to air dry, ensure the shells have completely cooled before adding them back into the tank. They can hold boiled water deep inside the shell, so it is important that the shells are completely cooled first.
If there is still some dirt or debris in the opening of the shell, give it a wipe down with some paper towel or a cotton bud.
NEVER boil old shells that have been taken out of your tank, small hermit crabs can sometimes hide in shells that are far too big for them and may not be visible when you remove the shell from the tank, if you boil these shells and there is a crab inside, they will burn to death.
Soak old shells in marine salted primed water for 10 minutes and let air dry on a towel before placing back into the tank. By soaking them in salted water, this will give them a fresh smell and entice your crabbies to check them out.
Place the shells into the tank with the opening side facing up to entice your crabs to try them on.
Pictured below is the exact reason why you should never boil shells taken out of your tank.
* A perfect example of a Hermit Crab hidden inside of a shell that is far too big, you cannot see the crab, but there is actually a small crab inside of this shell.
If you notice your crab chipping away at their shell, don't worry, Hermit Crabs love to alter their shells to fit the way that they prefer. Infact, most Hermit Crabs prefer to wear pre-loved shells that other crabs have altered and dropped.
Shells are full of calcium, so this will not harm your crab, unless the shell is painted.
Setting up a Shell Shop
Let's face it, we all love shopping! And so do our hermies. So, setting up a shell shop is a must! You can place your shells directly onto the substrate, in a bowl, on a platform or second level or just about anywhere that is accessible.
The good old saying applies here, "they will do it when they are ready, not when you are ready." We cannot force our crabs to change shells, they will change when they feel the time is right, even if it means they are in a shell that is far too small or painted. Sometimes they find those perfect pair of pants and they just aren't ready to let them go. Some crabs will change their shells on the daily, sometimes multiple times a day, this is nothing to be worried about, they are simply shell shopping to figure out what they like.
When a Hermit Crab finds a shell that they like, they will turn it over again and again to look at it and measure it up, you will often see them put their legs and face into the new shell headfirst, this is their way of measuring the shell up. If they decide that it is worth a try, they will get as close to the shell opening as possible and quickly within a matter of seconds, will come out of their old shell and plop their bums into the new shell. This is such an exciting and interesting event to witness.
When to Remove Shells
Perhaps your crab is running around in a painted shell, broken shell, cracked shell or a shell that has a hole in it. This can be incredibly frustrating, but when they change shells, you need to be careful at how quickly you take out their old shell to dispose of it. As above, crabs will shop around for that perfect shell, and they may have buyer's remorse after picking one and will want to go back to their old shell. If the shell they came from is painted, we recommend leaving it in the tank for at least 12-24 hours to see if your crab goes back to it or if they are happy with their new shell. If they stick with the new shell, remove the painted one and bin it. The reasoning for this is, if your crab cannot find their old shell and becomes stressed by the situation, they may very well go naked.
If their old shell is heavily damaged with breaks, cracks or holes, it is recommended to remove it shortly after they have changed, in the long run, this is safer for them as some damaged shells can dry out their abdomen, injure the crab and leak shell water.