Hermit crabs make adorable pets and are fascinating creatures in the wild as well. As any expert knows, hermit crabs will leave their shells at particular points in their lifetime.
In this article, we will explore the few circumstances that might prompt a hermit crab to leave its shell. Remember, shells are protective for hermit crabs and it is instinctual for them to want to remain inside.
We will also look at what we can do as good hermit crab stewards to facilitate healthy shell changes. As a good rule of thumb — and one that we want to provide right away in this article — you should have at least three additional shells available for every hermit crab in your tank.
Keep reading for lots more information about hermit crabs and their shells!
Why Do Hermit Crabs Need Shells?
Hermit crabs need shells primarily for protection. In the wild, hermit crabs encounter many situations that can kill them, and inhabiting a shell is one way that the hermit crab has evolved to survive.
You might be wondering, if your hermit crabs are protected from all predators in their tank, why do they still need a shell?
For one thing, inhabiting a shell is part of their natural instinct and they don’t have the reasoning capabilities to learn that they don’t need it anymore. Not being in a shell would be very stressful for a hermit crab.
For another, their shells also protect against other threats such as weather, accidents, and some forms of bacteria.
Why Hermit Crabs Leave Their Shells, #1: It Is Molting and Needs a New Shell
The number-one reason why a hermit crab leaves its shell is because it is molting and seeking a new one.
As with many animals, hermit crabs molt, meaning that they shed their hard outer layer called the exoskeleton. The first step in this process is not really visible as they store extra water and nutrients that they will need through the entire process.
Next, they shed their exoskeleton. Often, they will find a smaller shell at this point.
Hermit crabs might actually inhabit a couple of shells during the molting process. When they first go through the process of molting, because they have shed their hard outer layer without growing a new one, they actually need a smaller shell before they find their more permanent new home.
In addition, a smaller shell makes it easier to complete the next stage of molting: they bury themselves in the sand in order to be safe from predators during this especially vulnerable phase. A smaller shell means less “baggage” when they do this, and a shell with a smaller opening will let less sand inside.
Next, the hermit crab finds its new shell home! Keep reading below for a lot more information about that process.
Why Hermit Crabs Leave Their Shells, #2: It Has Found a Better Shell
Depending on the species of hermit crabs, some will change their shell simply because they have found another one that they have deemed to be better.
There isn’t a great way to predict when this will happen, though the longer they have inhabited their current shell, the higher the likelihood that they will stumble upon a better one.
The Purple Pincher, or Caribbean Hermit Crab, is well known for this habit. This is one reason why it is important and helpful to know what kind of hermit crab you have so that you can take the best possible care of it.
Hermit crabs also do a “house-hunting” behavior. After they molt and then grow their new hard outer layer, they may change shells several times, trying out different “homes” before they decide on a shell to inhabit for the foreseeable future.
They can even change shells several times a day during this phase.
How Often Do Hermit Crabs Need to Change Shells?
Hermit crabs need to change their shells about every 12 to 18 months. Finding and inhabiting a new shell is part of the molting process, which we discussed above.
Obviously, hermit crabs will change shells more often right after molting since they’re looking for their new home.
There’s no reason to worry about your crab if they seem indecisive about their new shells. Finding a new shell is instinctual for hermit crabs, so you can trust that if you’ve made several available (we discuss how many below), they will make a good decision in due time.
Why Hermit Crabs Leave Their Shells, #3: It Is About to Die
All pet owners wish that they could keep their animal companions forever. We understand!
Unfortunately, all living things have limited lifespans. Just as wild canines will leave their packs and retreat into the wild alone to die, crabs also have instincts: most notably, they leave their shells.
The good news is that hermit crabs have relatively long lifespans, especially compared to other common animals kept as pets. In the wild, they can live up to 30 years.
They usually don’t live as long in captivity — about two or three years — but some have been known to get as old as 20 despite living in a tank. The better care you take and the more you create an environment that resembles their natural habitat, the longer they will live.
How to Facilitate Shell Changes
As a responsible hermit crab keeper, it’s your job to make the process of shell changes in your aquarium or terrarium resemble the process in the wild as closely as possible. In order to do this, there are a few important things that you need to do.
First, you should make a steady supply of shells available to your crabs. There should be at least three shells available for every crab, in varying sizes.
You also need to have a sufficient amount of the right kind of substrate. As discussed above, hermit crabs will bury themselves during part of this process and they need the right environment in which to do it.
Another reason why it is important to know your breed of hermit crab: different types prefer different types of shells. As you learn more about the particular habits of your type of crab, you can also learn about the types of shells they prefer and buy or choose accordingly.
As tempting as it may be, don’t buy painted shells. Even paint that is supposed to be safe for marine life could actually be harmful and it isn’t worth the risk.
You must keep the shells clean. Make shell cleaning part of your routine tank maintenance by boiling them for about 15 minutes in plain water every eight weeks or so.
Clean new shells using the same procedure, especially if you brought them home from the beach.
Shell changes are very important to a hermit crab’s overall health. If they remain too long in the same shell, it causes serious problems for them that can lead to death, and if they can’t find a new shell that they deem suitable, they will remain too long in their current shell.
What If My Hermit Crab Hasn’t Changed Shells in a Long Time?
It is perfectly normal for pet owners to fret over their beloved animals, so if you’re closely monitoring your hermit crab’s molting, that’s normal behavior for you!
If you notice that your hermit crab hasn’t changed its shell in a while (more than 18 months), don’t panic. The first thing that you should probably do is make more shells available, just in case your crab doesn’t like any of the ones in the tank.
Again, know your crab, as some species of hermit crabs don’t change shells every time they molt. For example, the Ecuadorian hermit crabs will sometimes return to the same shell after they molt, and others will take longer to molt.
If you’re really worried about your crab, there is a trick that you can use to see if they need to change shells. This process should only be done rarely, since it is very stressful for your poor hermit crab.
To check and see if your hermit crab needs a new shell, pick it up by the end of the shell and flip it over so that the opening of the shell faces up. If your crab is happy and comfortable in its little home, its body and all appendages will retreat inside the shell.
If not, it’s probably time for them to find a new home. Make sure that there are plenty of options available.
Can I Make My Hermit Crab Change Shells?
No! You definitely cannot force your hermit crab to change shells, even if you are certain that they need to do so.
It is pointless to try to force your hermit crab out of its shell. You would more than likely kill or seriously injure your crab in the process.
Your hermit crab knows what it is doing, and as long as you have taken all the steps to properly care for your crab and encourage proper shell hygiene, they will do it on their own time.
I have a bachelor’s degree in Film/Video/Media Studies, as well as an associates degree in Communications. I began producing videos and musical recordings nearly 15 years ago. I am a guitarist and bassist in Southwest MI and have been in a few different bands since 2009, and in 2012 I began building custom guitars and basses in my home workshop as well. When I’m home, I love spending time with my three pets (a dog, cat, and snake) and gardening in my backyard. I also like photographing wild birds, especially birds of prey.