Hermit Crab Shells: What You Need to Know

Hermit Crab Shells (city on the back - Aki Inomata)

Perhaps one of the most important aspects of owning a hermit crab is what kind of shells you provide for your pet’s home. There are many questions that owners are faced with in this important decision, like what kind of shell the owner should provide and where to obtain them, etc.

In this article, we will go over the do’s and don’ts of hermit crab shells.

Why Do Hermits Crabs Need Shells?

Hermit crabs need shells in order to protect their soft and vulnerable abdomen. In the wild, the shell of a hermit crab acts as a defense mechanism against predators. In addition to protecting hermit crabs, the shell also helps to preserve the crab’s moisture. Hermit crabs will carry small amounts of water in their shells to keep their abdomen and gills moist so that they can breathe outside of water.

Since a hermit crabs shell serves so many important functions in its life, they have developed structures to ensure that they keep these shells. Hermit crabs have small hooks on their abdomens which give them a strong grip on their shells. It is important to never attempt to separate your crab from its shell. This would be extremely stressful for your crab and may even cause injury to your pet.

How Often Will My Hermit Crab Change Shells?

Hermit crabs will eventually switch shells on their own for a variety of different reasons. The most common reason for a hermit crab to switch shells is that the hermit crab grew larger and needs more space to accommodate their growing body. Hermit crabs will often change shells to molt, as smaller shells are more conducive to the molting process. And sometimes, hermit crabs will switch shells for no apparent reason other than trying out a new shell.

The most common kind of domestic crab- the Caribbean Hermit Crab- change shells quite frequently and will often trade amongst themselves if you have several crabs in a tank. Other kinds of hermit crabs (for example, Ecuadorian crabs) will likely change less frequently, though this varies between different breeds.

Important: Never try to force a crab to switch shells. Even if you have decided that the shell is not appropriate for your crab, you have to leave this up to them to change when they are ready.

What Kind of Shell Should I Buy for My Hermit Crab?

The shape of a hermit crabs shell can affect the shape of the crab’s body for life, so it is important to choose your pet’s shell carefully. Hermit crabs will generally feel most comfortable in shells that are the same shape as the shells that they grew into as a young crab.

If you do not know what kind of shell your crab grew into, try a variety of different shell shapes to see which kind your crab prefers. Some species of hermit crab can even carve out the inside of their shells to better suit the shape of their abdomen.

Note: In general, one of the main things that you need to look out for your crab is to make sure that the shell opening that the crab slips into is large enough, round and easy for them to get in.

Caribbean Hermit Crabs Shells Preference

Ecuadorian Hermit Crabs Shells PreferenceFor Caribbean Hermit Crabs, the best kind of shell to purchase is a turbo shell. Turbo shells are distinguished by a round opening and tight spiral toward the right. These shells often have mother of pearl lining the inside of the shell, an added bonus that will make your crab more comfortable.

Note: There are many types of turbo shells – Murex shells, Turbo Stripe, Green Turbo, Turbo Petholatus, Jade Turbo, Turbo Sarmaticus, Pugilina Cochlium, etc.

Ecuadorian Hermit Crabs Shells Preference

Ecuadorian Hermit Crabs Shells PreferenceIf you have a rarer or more exotic breed of hermit crab, it is a good idea to do research into what kind of shells they prefer, as hermit crabs can be very picky about their shells and will not thrive with the wrong kind of shell. For example, the Ecuadorian hermit crab (Coenobita compressus) prefers shells with D-shaped openings (oval shape shells) because their bodies are flatter and it suits them better.

Note: For example, Shark Eye shells, Nerita Polita shells, Nutmeg shells, Babylonia shells, Whale Eye shells, Nutmeg shells, etc.

The size of the shell will depend on crab and their stage in life. It is generally a good idea to have many options available for your crabs to ensure that they are comfortable as they grow.

What Kind of Shells Should I Avoid?

There are many types of shells you need to avoid when it comes to hermit crabs keeping. Some of these shells hermit crabs cannot or will not use. Others you need to remove yourself. Although there will always be exceptions to these rules, they are still exceptions, therefore, – inappropriate.

Hermit crabs Shells to avoid

Painted Shells

One of the most common misconceptions about buying hermit crab shells is that painted shells are an acceptable choice for pet hermit crabs. Many stores sell painted shells, particularly in tourist areas where hermit crabs are commonly sold. Additionally, many well-meaning owners paint their own shells to provide a fun and colorful accessory for their beloved pet. We cannot stress enough how dangerous these practices are.

While a number of health problems can arise with painted shells, one of the most common occurs when paint on the shells chips off and the hermit crab within the shell consumes the paint chips. Hermit crabs are scavengers and accordingly, will eat anything they can get their claws on- even toxic paint chips. These flakes of paint may seem too small to do any real damage, but hermit crabs are extremely sensitive to chemicals of any kind. Seasoned owners know that hermit crabs cannot even withstand chlorine in their tanks, so it is important to not take any risks with potentially dangerous chemicals around your pet.

If you were unaware about the dangers of painted shells, do not panic yet. Simply introduce a new shell for your crab, and once it switches shells, remove the painted shell from the tank and clean any paint chips that you see.

Similarly, while glass shells make a lovely tank decoration, most crabs will not move into a glass shell. They do not pose any danger to your crab, but it should be noted that they are not a practical option for most crabs.

Note: Do not confuse painted shells with polished ones. They will not hurt your hermit crab. However, if shells are painted with a clear gloss (lacquer), it is extremely toxic to hermit crabs!

Shells with Ridges

Shells with ridges on the bottom half of the shell are also generally a nonstarter for hermit crabs. Since hermit crabs use their shells to protect their soft and sensitive abdomens, a shell with large ridges is going to irritate these tender areas and be very uncomfortable for the animal. While some hermit crabs might use shells with less pronounced ridges, it is generally a good idea to stick with softer shells – particularly those lined with smooth mother of pearl.

Land snail shells

Avoid the shells made by land snails. These shells have thin walls than those made by sea snails. Land snail shells do not hold the moisture in for them and more prone to breaking. In some cases, hermit crabs prefer to eat them (as a calcium source) instead of wearing them. 

Shells with Narrow Openings

You do not want to get a shell that has a very long and narrow opening. Hermit crabs simply cannot fit in these openings.

Long Shells

Although these shells are very spacious, hermit crabs do not usually choose them when given a choice.

Cone Shell

Small hermit crabs sometimes use them but if hermit crabs have a choice, they pick another one. These shells are very heavy with small openings.

Spiky Shells

The main problem with this type of shells is that hermit crabs will have a hard time maneuver. The spike will always impede the movement.

Nautilus Shells

Internally, the nautilus shell divides into cameras (the chambered section). As the nautilus matures, it makes a new chamber and seals the vacated chamber. The chambers increase in number from around 4 at the moment of hatching to 30 – 35 or more in adults. Basically, the internal structure of the nautilus shells makes it nearly impossible for a hermit crab to hang onto.

Glass Shells

The glass shells will not be the best option as well. Of course, these shells look super cool, especially 3D shell by Japanese artists Aki Inomata. Nonetheless, in reality, hermit crabs do not like the glass shells because they do not feel like they can hide in them.

Damaged Shells

Damaged shells should be removed without question. These shells can damage their abdomen and end up killing them.

Where Should I Buy my Hermit Crab Shells?

Surprisingly, large pet store chains are generally not the best places to buy hermit crab shells that your pets will want to use. These stores often sell shells that are in the wrong shape for most hermit crab bodies, or worse, dangerous painted shells.

Craft stores can be an excellent source of shells for pet owners looking to shop in person. These stores are somewhat limited in what they offer and the kinds of shells that you can find in craft stores will usually only work for smaller hermit crabs, but good turbo shells are fairly common in most craft stores.

If neither of these options works for you and your pet, online stores have the largest selection of hermit crab shells for crabs of a variety of different species.

How to Measure Hermit Crab Shells?

First of all, we do not measure shells from tip to tip. You need to make sure the opening is big enough for them to get in. So, what you are going to do is measure the widest part of the mouth of your shell at the longest point.

You need to know the size you are looking for. Therefore, measure the widest part of the mouth of your shell your hermit crab is currently in. So if it as an inch wide you need to buy shells that are a bit bigger. You can also experiment with other shells like this kind.

Tip: Do not just buy shells, which are slightly bigger. Buy shells that are a little bit more bigger as well. As the hermit crab grows, obviously it will need more space.

Ideally, their big pincers should seal off the opening if it is a good fitting shell.  If hermit crabs cannot withdraw into the shell, it means that the shell is too small. Therefore, it offers them no protection from predators and even other hermit crabs.

How Many Shells Should I Keep in my Tank?

If you are planning to keep multiple crabs in the same tank, it is important to provide them with a variety of shells to avoid fighting among your pets. In the wild, hermit crabs can be very competitive over shells and these aggressive behaviors transfer over to hermit crabs in captivity. To mitigate the risk of shell fights, it is a good idea to keep a large number of shells –  around 2 – 3 per crab at a minimum – in the tank at all times and to rotate out different shells to keep your crabs interested.

If you do experience hermit crab fights, stay calm and separate the crabs. If you notice that the crabs continue to fight after being separated, you will need to isolate one of the two crabs. It is best to separate the crab that is the victim of the shell fight so that they have time to recover away without worrying about their safety.

A good way to deter the aggressor crab is to provide them with a shell that is identical to the shell of their victim. Ideally, the aggressor crab will move into this shell and lose interest in the victim crab’s shell, a solution that has benefits for all parties.

Tip: Do not remove small shells from the tank. Before Hermit crabs molt, sometimes they will move into smaller shells. It is easier for them to bury with a smaller shell. Once they molt and come up, they will replace it with a larger shell.

Cleaning Hermit Crab Shells

This habit has the added bonus of giving you a chance to clean shells on a regular basis. One thing to note when cleaning your crabs’ shells is that the tap water most owners use when cleaning their crabs’ shells likely contains chlorine, a chemical that is extremely hazardous for hermit crabs.

To avoid inadvertently poisoning your crabs with chlorine, allow at least 24 hours after cleaning for the shells to dry and any toxic chlorine to evaporate. Likewise, you should never use soap when cleaning your crabs’ shells to avoid leaving trace chemicals in the shell.

The best methods for cleaning your hermit crabs’ shells are either simply rinsing the shells or using boiling water (5 – 10 min) to thoroughly disinfect shells if needed.

Tip: Put a rag or something inside the pot, if you are going to boil shells. It will prevent any markings when a shell presses against the side of the pot. 

In Conclusion

Hermit crabs are fun and relatively easy to care for pets for owners with a bit of background knowledge. When it comes to hermit crab shells, knowing something about the kind of shell your crab prefers will go a long way in enhancing the comfort of your pet.

Related Posts:

Hermit Crabs–Detailed Guide: Care, Diet, and Breeding
Everything About Hermit Crab Molting
Hermit Crab Tank Setup

Hermit Crab Diet

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