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Where Do Hermit Crab Shells Come From? (An In-Depth Look)

Where Do Hermit Crab Shells Come From? (An In-Depth Look)

The purpose of this blog is to share general information and is written to the author's best knowledge. It is not intended to be used in place of veterinary advice. For health concerns, please seek proper veterinary care.

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Did you know that hermit crabs aren’t actually “crabs”?

That’s right, hermit crabs are more closely related to some types of lobsters, such as squat lobsters. This is because the bodies of hermit crabs don’t have hard exoskeletons all over and they can’t grow shells on their own like true crabs.

Instead, hermit crabs have soft, shell-less abdomens with only the front halves of their bodies covered in a hard exoskeleton As for the exposed tail sections of a hermit crab, a shell is a must to provide protection among other benefits.

This brings us to today’s question: where do hermit crab shells come from?

To answer, we have to take a closer look at these cute crustaceans and their fascinating behaviors.

Today’s article explains the importance of a shell for hermit crabs, why these animals change shells, where they get shells, how to help your hermit crab into a shell, and a lot more.

Why Are Shells Important for Hermit Crabs?

If you keep a hermit crab or you’ve ever seen one, chances are it was carrying a shell on its back. You may be surprised to learn that hermit crabs don’t grow their own shells, and as such, aren’t considered true crabs but more resemble lobsters.

Hermit crabs have soft abdomens. Only the front half of their bodies feature a hard exoskeleton, the other half that contains the tail is exposed and vulnerable to predators and elements of the environment.

The lack of a self-made shell is just one of the two reasons why the name “hermit crab” is a miss for these crustaceans. The second reason is that hermit crabs are mostly social animals that like to live in large groups, sometimes of more than 100 members in the wild.

As such, hermit crabs aren’t even hermits, which is a term referring to people who choose to live in solitude and rarely interact with others.

Back to our question, why are shells important for hermit crabs?

Well, hermit crabs need shells for the same purpose other shelled crabs do — protection.

Shells offer protection for the soft, exposed portions of a hermit crab’s body that’d otherwise be prone to attacks by other animals and elements of the environment.

A shell is extremely valuable for a hermit crab’s sense of security. If you own one of these crustaceans, you probably know how much they like to hide in their shells whenever something happens around them (for example, you moving fast around them) and they feel threatened.

A hermit crab without its shell isn’t just at risk of serious injury and possible fatality from predators and even other hermit crabs during conflicts or normal behavior, but also from the harmful effects of unshielded exposure to sun rays, heat, and air.

What’s more, a hermit crab’s shell allows it to store water for later use when there’s none around, for example, during underground molting that may last several weeks or a few months.

In such a case, the shell keeps its hermit crab alive as it prevents its sensitive body from drying out.

The shell of a hermit crab can also facilitate its camouflage. This happens when these crustaceans decide to carry sea anemone on their shells for an extra layer of protection, forming a sort of a second shell known as carcinoecium.

Do Hermit Crabs Start Out Their Life With a Shell?

Since shells are so important for the survival and well-being of hermit crabs, does this mean they get a shell right when they’re born?

The answer is no.

You already know by now that hermit crabs are born without shells because they can’t grow them. So what happens to baby hermit crabs that are shell-less and just starting their life?

Here’s a breakdown of the stages of a young hermit crab’s life to help you understand:

Zoeae

This is the first form of a hermit crab. It occurs when the females carrying the eggs go to the edge of the sea to allow the eggs to burst upon making contact with salt water.

When the eggs explode, they release tiny larvae called zoeae. From this point, zoeae join plankton and float at and beneath the surface of the water.

Since zoeae can’t propel themselves, they’re displaced around the ocean by the water’s current with plankton and mainly serve as food to various small and large aquatic animals.

Megalopa

Of course, not all zoeae end up getting eaten. The ones that manage to survive for about 2 months become what’s referred to as megalopa.

Megalopa is the life stage at which tiny hermit crabs find their first shell.

According to the Journal of Experimental Marine Biology and Ecology, a megalopa exhibits 3 behaviors:

  • Shell inspection
  • Shell wearing in water
  • Shell wearing on land

This means that a megalopa finds and carries its first shell while in the water.

In most cases, this first shell comes from a sea snail that left its shell. The size of a sea snail’s shell is small enough to accommodate the fingernail-like size of a hermit crab in the megalopa stage.

The shell provides protection for the megalopa once it goes out on land. To get used to the terrestrial environment, the megalopa will develop lungs and adapted gills.

Hermit crabs stay megalopa for around a month, after which they burrow into the sand and molt if they’re still alive.

Once they get out from being buried, the molted megalopa is now a juvenile hermit crab. Young hermit crabs, like all juvenile animals, need to fend off predators so they must quickly find a sturdy, empty shell to survive.

From this point, the hermit crab starts going through the normal, constant cycle of shell wearing and vacating as it grows in size and reaches adulthood.

Sometimes, hermit crabs will slow down their growth on purpose to stay relatively smaller in size than others. This phenomenon is known as delayed metamorphosis.

The reason behind this is to keep their chances of finding a shell high. You see, the smaller a hermit crab is, the easier it can find a shell to fit in and the more abundant its options.

The bigger the juvenile hermit crab, the harder the time it’ll have trying to find a shell because medium ones are tough to come by while large ones are targeted by adult hermit crabs that’ll most definitely dominate the younger hermit crab in a showdown.

Why Do Hermit Crabs Leave Their Shells?

With all the effort that hermit crabs spend to find a suitable shell, you’d think they’d never leave it unless to trade it for a bigger shell as its body naturally grows too big for the current shell.

However, there are a bunch of other reasons that can drive a hermit crab to abandon its shell. It may have to do with environmental conditions, health state, or even mood.

Knowing what could be causing your hermit crab to leave its shell is a crucial part of caring for your pet and preventing such behavior in the future. Here are the most common reasons hermit crabs ditch their shells:

1 – Stress

Stressful conditions can push a hermit crab to leave its shell. This could’ve happened before you picked it up from the pet store, probably during shipment, distribution, or storage actions.

If the circumstances of these activities are poor, such as providing improper care or causing physical trauma, unhealthy hermit crabs can get so stressed out that they abandon their shells to die.

As such, you should only deal with trustworthy suppliers with a good record of handling these delicate creatures.

2 – Irritating Shells

The shells of hermit crabs aren’t usually a perfect fit. They’re often a bit displaced off of their bodies, allowing small particles and debris to get inside the shell.

These particles and debris can cause irritation to the hermit crab carrying the shell. As a result, the crustacean tries to eliminate the disturbance by getting rid of its sources, which happens to be its shell.

To prevent your hermit crab from leaving its shell out of irritation, make sure to periodically clean the inside of the shell to remove any small, annoying particles. Don’t forget to be extra gentle when doing this to avoid stressing your pet.

3 – Conflict With Other Hermit Crabs

If you own multiple hermit crabs, they may possess different growth rates. In this case, not providing them with enough space and shells can cause conflicts to erupt.

These conflicts can easily trigger the hermit crabs to start fighting each other over their shells. Such battles can lead to serious injuries and maybe even death.

4 – Unfavorable Conditions

Hermit crabs require certain environmental conditions to thrive, one of the most prominent being the temperature of the tank.

You see, these crustaceans are ectothermic. This means they rely on their environment for heat regulation within their bodies.

As such, hermit crabs need both hot (no more than 85 degrees F) and cool (no less than 70 degrees F) areas inside their enclosure at the same time so they can move between them depending on their bodily requirements at a given moment.

If the temperature inside the tank gets too high or too low, your hermit crabs may become too uncomfortable that they exit their shells as a response.

5 – Molting

Molting for a hermit crab molts is a phenomenon where the crustacean sheds its current exoskeleton and grows a new one. This process is typically followed by a significant increase in the hermit crab’s size, which means it’ll need a new shell to accommodate its growth.

If you’re suspecting that one of your hermit crabs is entering a molt, you can notice some clues such as increased intake of food and water, excessive digging, and becoming lazy.

Physically, a hermit crab preparing to molt will show a fading exoskeleton to a dull gray color, usually accompanied by a glazed look in its eyes.

In this case, you should make sure that the molting hermit crab remains undisturbed. So before the molt starts, separate the molting hermit crab from the rest.

Once the molt ends, provide the emerging hermit crab with a few bigger shells as it’ll come out missing a shell. It’ll have exited its previous shell, so you can recycle it for a younger hermit crab if it hasn’t been damaged during molting.

Return the hermit crab to its tankmates only after it has settled into a shell.

6 – Death

As much as you may not want to think about it, your hermit crab will leave the world at some point. When this happens, you’ll see that its body falls out of its shell.

The reason may be a sickness that you didn’t notice or simply old age.

7 – General Upgrade

Last but not least, a hermit crab may abandon its shell to look for a better one that offers more protection or weighs less for improved mobility. The hermit crab may even do it out of boredom and need for a change.

As such, you’re responsible for providing various shapes and sizes of shells for your hermit crabs to give them the necessary flexibility when finding a suitable shell.

Where Do Hermit Crab Shells Come From?

In enclosures, such as the tank you prepare for your hermit crabs, these crustaceans get their shells from the shells that you provide for them. You can buy shells from pet stores, craft shops, or online vendors.

In the wild, hermit crabs acquire shells in one of the following ways:

1 – Scavenging

Scavenging is the main practice of hermit crabs when it comes to looking for new shells. It’s such an integral part of this animal’s life routine that a lot of hermit crabs choose to live in areas with an abundance of shells to go through.

Sometimes, there’s nothing even wrong with the hermit crab’s current shell and it decides to make a switch. It’d be roaming around for food and meanwhile stumble across a more suitable shell so it leaves its current shelter for this new and improved one.

The source of the new shell could be a dead crustacean or a vacant seashell. If the hermit crab wears the new shell but doesn’t like it right away, it can simply return to its old one before another hermit crab claims it.

The only problem is that hermit crabs can get confused when scavenging and think that trash such as plastic bottles is a shell. Unfortunately, this can cause death as the hermit crab is unable to get out.

2 – Battling Other Hermit Crabs

As we mentioned earlier, hermit crabs are social animals that enjoy living in large groups.

Sometimes, the presence of many hermit crabs in the same place can lead to conflicts between them, and consequently, fights. When this happens, hermit crabs demonstrate shell rapping where the more dominant hermit crab knocks on the shell of its less dominant opponent.

This behavior can occur when a hermit crab outgrows its current shell and wants to move to a larger shell that already belongs to another hermit crab. So, the first hermit crab will challenge the second by hitting its shells.

If the first hermit crab wins, the two will exchange shells. However, this doesn’t necessarily mean that the second hermit crab actually loses. It could very well be happy with its new shell, making everyone happy and winners.

3 – Locating Dead Hermit Crabs

Finally, a hermit crab can get a new shell by taking over the shell of another hermit crab that died.

How does a hermit crab know you ask? Well, dead hermit crabs release a unique pheromone that helps other hermit crabs know it’s dead so they can make their way to the body to inspect its shell if they want to.

In other words, a dead hermit crab announces that its shell is up for grabs by releasing a death scent. The purpose of this is to support the continuity of life for other hermit crabs in the colony.

Why let a perfectly functioning shell go to waste when a fellow hermit crab can survive because of it?

How to Help Your Hermit Crab Into a Shell

If your hermit crab has left its shell and you’re trying to get it to wear a new one or return to its current shell, follow the steps below:

  • Make sure you’re extra gentle with your hermit crab since its body is very fragile without a shell and can easily get injured if you’re not careful.
  • Boil the shell in dechlorinated water to get rid of any debris or bacteria.
  • Prepare a container that’s just roomy enough for the hermit crab and shell.
  • Add some dechlorinated water to the container to only cover the bottom.
  • Place the hermit crab and the shell in the container.
  • Don’t disturb it and just wait for the re-shelling to happen.

Final Thoughts

So where do hermit crab shells come from? As you can tell by now, the answer depends on the age of the hermit crab and its surrounding environment.

At the beginning of their lids, hermit crabs get their shells from the ocean. After that, they acquire shells from scavenging beaches, fighting other hermit crabs, and locating dead hermit crabs.

If you own pet hermit crabs, you can buy them shells from pet stores, craft shops, or online vendors.