Home » How Does A Hermit Crab Molt Its Exoskeleton?
how long is the molting process for hermit crabs?

How Does A Hermit Crab Molt Its Exoskeleton?

Part of what makes hermit crabs so fascinating is how they molt their exoskeleton, which is a process is integral to a hermit crab’s growth.

In fact, the average hermit crab spends up to 90% of its life preparing to molt, molting, or recovering from molting. So, you may wonder what the hermit crab molting process looks like.

Molting comes to a head when a hermit crab’s exoskeleton cracks, and it slowly pulls free of it. Once it has shed its old exoskeleton, the hermit crab will absorb water into its soft flesh. This will increase its size before forming a new exoskeleton.

This can take 4-8 weeks to complete and will happen again every 12-18 months on average.

Hermit crabs molt on the surface or underground. As it prepares to molt, it’ll undergo physical and behavioral changes.

The signs of an oncoming molt phase aren’t always the same. It may alter its eating habits, switch shells more frequently, develop a fat pouch, or regenerate lost limbs.

Why Does a Hermit Crab Molt?

Hermit crabs shed their exoskeletons for these three reasons:


A hermit crab will molt in order to grow. The hard carapace of the exoskeleton protects the hermit crab, but it’s also very restrictive. As a result, hermit crabs must regularly shed this hard outer skin to grow in size. If they did not, they would be crushed by their own exoskeleton.

For contrast, imagine your own adolescent growth spurt. Your human body stretched and grew in mass, all in a continuous stage. However, a hermit crab’s exoskeleton works more like armor than skin. The hermit crab must recreate a new layer of protection in a new, more optimal size once it’s grown.

Once hermit crabs shed the original exoskeleton, they expose soft, pliable flesh. The hermit crab will then absorb water to make its flesh swell. By doing this, it increases its size before forming a fresh carapace over the top.

how often do hermit crabs molt?

Brood Success

Research published by Satoshi Wada in Marine Biology also reveals new advantages. The study suggests that molting is important for fertility and brood success in female hermit crabs.

Wada initially stated that molting shortly after breeding could increase the success rate of that brood by clearing pleopods from the female. That, or it may increase future brood success at the expense of this one. In the end, Wada found the second hypothesis to be true.

This shows that molting is just as important to hermit crab brood success as shell size. This was shown by research published in Ecology to affect the size of egg clutches. Of course, unless you intend to breed your hermit crabs, the main purpose of molting is for a hermit crab will be to grow larger.

Stress or Injury

Stress or injury itself will not cause the hermit crab to molt. However, this is one of the main advantages to molting and a good motivation for hermies. Hermit crabs use this as a chance to heal.

For example, your hermit crab has encountered a sickness, lost a limb, or has been put under stress. In this case, the hermie will try to weather these trials until its next molting cycle. Once this time comes, the hermie will then undergo its standard molting procedure. After that, it will emerge healthier and whole.

Why Is My Hermit Crab Smaller After Molting?

It is normal for your hermit crab to look smaller when it emerges after molting. When it first starts to be active again, your hermit crab will not have formed its new exoskeleton perfectly yet. It still needs to take on water and refuel.

Over the next few days, you will notice a change in the size and coloration. This happens as a new exoskeleton forms over this tender flesh. After forming a new exoskeleton, your hermit crab may seek a larger shell in which to live. Hermit crabs will molt several times throughout their lives. So, they never stop growing.  

The Hermit Crab Molting Cycle

Most hermit crabs go through a cycle of molting every 12 to 18 months. Hermies can molt in two ways:

  • Above ground
  • Underground

Subterranean molting is preferable because it is safer and less stressful. Hermit crabs that molt above ground may be sick or stressed out. In any case, the molting cycle of any hermit crab has three main phases:

  • The pre-molt phase
  • The molting phase
  • The post-molt phase

Each phase has its own set of physical and behavioral indicators to watch out for. Remember, this is one of the most stressful and taxing periods of your hermit crab’s life. You mustn’t intervene., and there’s little a vet can do. The kindest approach for your hermit crab is to give it the best possible molting conditions.

Hermit Crab Molting Signs

During the pre-molting phase, your hermit crab may undergo a variety of physical and behavioral changes.


Physically speaking, a hermit crab preparing to molt will eat more than usual. It will then suddenly stop eating and become lethargic a few days before it molts.


Likewise, it may start digging holes and burying itself. This is called substrate testing. It is a strong sign of an impending subterranean molt.

Changing Shells

A hermit crab preparing to molt may also start changing shells frequently. Hermies will move to smaller shells. However, scientists don’t have a firm explanation of why, but it may be because they are easier to bury.

Fat Pouch

The hermit crab will likely form a fat pouch on the right side of its abdomen. This is a store of nutrients and water, which allows the hermit crab to feed during its most vulnerable stage. Hermit crabs cannot move while their exoskeleton is hardening. This could lead to starvation, but the fat pouch gives them a reprieve.

Limb Regeneration

Most impressively, hermit crabs can regenerate lost limbs during molting. This is a great way to prolong their lifespan, even after accidents or fights.


Your hermit crab will usually change color as it prepares to molt. It will look duller in shade and have slightly cloudy eyes.

How Does A Healthy Hermit Crab Molt?

Assuming your hermit crab is healthy and relaxed, it will bury itself to start the molting phase. Hermies do this because dark, wet, and warm conditions are ideal for successful, non-traumatic molting.

Furthermore, hiding in this way is safer. Molting is one of the most vulnerable moments in a hermit crab’s life cycle. If it’s exposed while shedding its exoskeleton, it can:

How Does A Sick Hermit Crab Molt?

If your hermit crab is ill or stressed, it may forgo burying itself. If you see your hermit crab beginning to molt above ground, do not attempt to bury it. It lacks the strength to dig or deal with cave-ins at this point. It could suffocate.

Instead, put any already-shed exoskeleton near the hermit crab, along with soft food. Cover the tank with a blanket to make it dark, as this will reduce stress. You should also remove other hermit crabs from the tank, as they may try to eat the molting one.

Hermit Crab Molting Care

Whether this is your first experience with molting hermit crabs or your hundredth, keep these tips in mind:

Make Sure Your Tank Is Large Enough

To avoid cannibalism, you should ideally have a large tank. It should have a deep substrate of around 6 inches. This allows each hermit crab enough space to burrow into the ground.

Here, it will be safe from other hermit crabs. If tanks are too small, other hermit crabs will dig them up by accident or on purpose to claim that molting spot.

Boost The Crab’s Diet

As the hermit crab enters the pre-molting stage, provide a rich diet. It must have plenty of calcium and protein. Your molting crab will need to rebuild its exoskeleton completely. Calcium will be essential in doing this, while protein will help keep the hermit crab energized.

Separate Your Crabs

If your hermit crabs are well-fed and given space, they shouldn’t dig each other up. However, some may possess a habit of doing this anyway. That’s why it’s good to have an isolation tank for hermit crabs ready to molt.

Your ISO tank should be a small version of the main habitat. If you miss this window and notice your hermit crab has already begun to molt, you can:

  • Move other hermit crabs
  • Block off the molting area (if in a corner)
  • Use the soda bottle isolation technique.

The Soda Bottle Technique

This should only be used within the first few days of molting. There is a chance you could collapse the hermie’s cave otherwise. It will not have the strength to rebuild once the molt is fully underway. As a result, it would be smothered to death in its collapsed cavern. Make sure your timing is right.

You will need the top half of a large soda bottle – the bigger, the better. It should be fully cleaned of all soda traces. Once you have this, sink it into the substrate around the hermit crab. This will quarantine it from the others, leaving the cap open for airflow.

This only works for small hermit crabs. Larger hermit crabs should be isolated in a quarantined area or an ISO tank.

How Long is the Molting Process for Hermit Crabs?

Molting is a personal process for hermit crabs. The time it takes to complete the full process, from preparation to recovery, can vary depending on the size of the hermit crab.

However, on average, a successful molting process will take from 4 to 8 weeks from beginning to end. A larger hermit crab may take longer to molt. Smaller hermit crabs can molt in half that time. However long it takes, your hermit crab will most likely stay buried for the majority of this process.

You may think the process is completed when your hermit crab emerges from its cave. That is not so. Once it emerges, it still has to bulk up its flesh and form a new exoskeleton. This will protect it from the stresses of daily life.

It is important to watch your hermie and do not handle it. Until the new exoskeleton has formed, doing so may cause injury by accident.

What To Do With Molted Hermit Crab Exoskeleton

A hermit crab will consume its own shed exoskeleton. This allows it to benefit from the minerals, salt, and calcium that the shell holds.

If your hermit crab has difficulty molting, you may find discarded fragments of the exoskeleton lying around it. In this case, you should place those fragments near to your hermie. This allows it to consume the nutrients and proceed with greater strength. If your hermit crab passes away after molting, you can either:

  • Leave the shed exoskeleton in the tank for others to consume
  • Discard it

Can a Hermit Crab Molt Inside its Shell?

A hermit crab does not abandon its shell to molt. However, it cannot use the shell as replacement protection for burrowing either.

Instead, it will need to bury or seclude itself to detach and shuck off the old exoskeleton and form a new one. The shell will remain on during this process. It may even serve as a “mold” for the hermit crab developing its exoskeleton.  

A molting hermit crab will often change its shell. Specifically, it will move to a smaller home, which is easier to bury. Many things can go wrong with this process. Let’s explore them down below:

Hermit Crab Molting Above Ground

Hermit crabs prefer to molt underground both in the wild and in domestic settings. So, it is unusual to see one molting above ground. If your hermit crab has begun the process, you should:

  • Make sure it is safe from other hermit crabs
  • Investigate reasons why

The most common reason for molting above ground is a lack of sand. Unless you provide around 6 inches, the hermit crab will not be able to dig an appropriate cave for molting. Assuming you do have enough substrate, the problem is likely with your hermit crab itself. Hermit crabs in poor health may molt above ground because they lack the energy to dig a suitable cave.

Molting above ground can also be caused by extremely high stress levels. An anxious hermit crab may be capable of digging. However, it could also be experiencing lethargy due to stress and thereby fail to build itself a cave. Signs of a stressed or ill hermit crab are:

  • Refusing to curl into its shell
  • Losing limbs
  • De-shelling itself (refusing to stay inside a shell)
  • Lethargy
  • Not eating

If you think your hermit crab is stressed or ill, assess its habitat and food to ensure it has everything it needs.

Hermit Crab Molted But Didn’t Change Shells

Hermit crabs are known for changing shells as they grow and mature. So, many people are shocked if their newly molted crab doesn’t abandon its smaller shell for a bigger one immediately.

Of course, in the wild, big shells can be hard to come by. In a domestic situation, a bigger shell should be immediately available. What if you have bigger shells available for your hermit crab, but it doesn’t make the change?

The Shells Are Too Heavy Or Overbalanced

The shells you’ve presented may not be suitable. A hermit crab uses the shell it inhabits to protect itself from the sun, predators, and other environmental dangers. Research undertaken by Michael Conover shows that weight and volume affect hermit crab shell selection.

Likewise, a shell’s center of gravity affects whether a hermit crab will choose it. If it is overbalanced, a hermit crab may pass on it.

hermit crab molting cycle

The Shells Are Too Thin

If a shell is too thin to provide protection, your hermit crab may not want to inhabit it. If the shell is too large (or small) for its needs, it will definitely stick with the one that it has.

Ensure that your hermit crabs have choices. A hermie will often shuffle around, trading shells with other hermit crabs until it finds one that suits it. If your hermit crabs refuse to change shells after molting, you should place a collection in the habitat.

Hermit Crab Molting Smell

When molting, a hermit crab will give off a certain smell. It can be alarming for those who are unused to it.

Don’t worry unless the smell is strongly fishy or rotten. The molting smell, by contrast, is more chemical – like epoxy or iodine. Though it can be strong, it is not necessarily unpleasant.

Is My Hermit Crab Molting or Dead?

It can be scary to pick up your hermit crab and have it fall out of its shell. In some cases, this may be because your hermit crab has died. More often than not, though, what falls out is actually a discarded exoskeleton.

Once molted, a hermit crab may seek a bigger, better shell to fit its sleek new look. For those new to these fascinating creatures, it can be hard to tell the difference. A hermit crab preparing to molt and a crab that is, in fact, dying can look very similar.

A molting crab, if caught above ground, will be limp and can appear lifeless. It can even be partly out of its shell while molting in this way. Look closer. You should be able to see small signs of life and movement in a molting hermit crab. However, if the hermit crab is buried, it will be tough to tell if it is dead or simply molting.

If unsure, the safest route to take is non-interference. Trying to move your hermit crab could be fatal. If your hermit crab has indeed died, it will begin to smell fishy and putrid within a day or two. Its abdomen will turn black. At this point, you can be sure that it has definitely died, and it can be removed from the habitat altogether.

My Hermit Crab Molted Then Died

Some species have a high mortality rate post-molting, like the giant river prawn. The World Mariculture Society has shown them to have a post-molt mortality rate of up to 50%. However, hermit crabs do not die after molting unless they are already ill or injured. If they do, it’s usually due to suffocation, cave-ins, or cannibalism.

What if your hermit crab died immediately after molting? There are a few explanations:

  • The temperature in the tank is too low
  • The saltwater mix is poorly balanced
  • Its food was insufficient or harmful to it
  • The tank is too small or improperly set up
  • The humidity is too low
  • You have too little substrate, or it is the wrong kind

Out of all of these, the most likely cause of post-molt death for a healthy hermit crab is:

  • Low temperature
  • Improper substrate
  • Lack of proper nutrition.

What can you do to minimize the chances of your hermit crab dying after a molt? Take these simple precautions:


Make sure your hermit crab has enough substrate. This should be matched to the correct degree of moisture. If the sand is too dry, your hermit crabs’ caves will crumble. If too wet, the hermie may not be able to form a cave for molting at all.

You should also avoid high calcium sand mixes. These can harden in a hermit crab’s joints and shell like cement, suffocating it.


Also, make sure your hermit crab habitat has the right temperature. For most species, the perfect conditions should be 75–85 Fahrenheit. Anything lower or higher will increase the likelihood of death after molting. If the temperature difference is extreme, it could kill all your hermit crabs.


In the wild, hermit crabs will eat almost anything they can get their claws on. This ranges from green and red algae to dead fish and shrimp. Therefore, it’s important to feed your hermit crabs a varied diet, especially with high protein foods. For example:

  • Fresh sardines
  • Plant matter like spirulina algae wafers
  • Dried seaweed

Vitamin-enriched pellets also make a great addition to fresh food.

Why Isn’t my Hermit Crab Molting?

Hermit crabs are complex animals. Many factors influence their molting cycle. Rarely will two hermit crabs will molt at the same rate. Likewise, they might not molt for the same reasons.

For example, Akira Asakura found that female hermit crabs molt more often than males. Molting is also more frequent during reproductive seasons.

Hermit crabs will molt once every 18 months. Smaller crabs could molt more frequently. Larger ones could molt at a reduced rate because of the energy required to undertake this process. If you’ve owned hermit crabs for less than one year, don’t be alarmed if they haven’t molted.

Very few things can prevent a hermit crab from molting. However, extreme malnutrition and stress may make it harder to molt successfully. It will also increase the chance that it will die during the process. The best approach is to give your crabs a safe and healthy environment.

Do Hermit Crab Molts Change Over Time?

The process of molting is the same for every hermit crab. The animal will move from:

  • The proecdysis (pre-molt) phase
  • To the metecdysis (post-molt) phase.

However, the time it takes to molt and the time between molts changes. This is based on:

You could notice an older hermit crab molting less often. Even if it used to molt in a couple of weeks, it may now require several weeks. As owners, our job is to learn how to provide the best environment for our pets. A molting diary can help you prepare more effectively.

What Is A Hermit Crab Molting Diary?

A molting diary for your hermit crabs is useful, especially if you are a new owner. Be sure to note your hermit crabs’:

  • Age
  • Size
  • When the molting process began
  • When it seems to end

Also, note changes in your hermit crabs’:

  • Eating habits
  • Digging habits
  • Activity before and after molting

As your hermit crabs age, you will have a reliable store of knowledge. This will help you to care for your other hermit crabs better in the future.