Skip to Content

Do Hermit Crabs Molt? (Breaking Down Each Phase)

Do Hermit Crabs Molt? (Breaking Down Each Phase)

Share this post:

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. In addition, as an Amazon Associate I earn from qualifying purchases.

Hermit crabs, like all crabs, get rid of their old skin every once in a while to rejuvenate themselves.

If your hermit crab hasn’t surfaced for a while or if it did with a different color, you’re probably curious.

Fret not, we’re going to uncover everything you want to know about the topic: Do hermit crabs molt?

Let’s look further into it.

What Is Hermit Crab Molting?

As the case is with many invertebrates, hermit crabs shed their exoskeleton. After this, they can’t move for a little while and lose all control over their muscles.

Then, their new exoskeleton toughens up and crabs regain control and resurface. They need to do this in order to grow and mature.

Why Do Hermit Crabs Molt?

Molting is how a hermit crab is able to grow or prepare itself for tackling a new life phase ahead. It sheds its outer layer and regenerates another one to maintain a healthy exterior to protect itself.

Molting isn’t only important for growth, but it’s also a way for hermit crabs to stay healthy. This is because they get rid of any parasites living within their exoskeleton, like tube worms and barnacles.

Moreover, molting is a way to fill in any missing segments in the crab’s shell. Not only that, but it’s also the time when they regenerate their legs and claws.

How Long Do Hermit Crabs Molt?

How long a hermit crab takes to molt depends a lot on the size of the crab. The rule of thumb is that the bigger the crab is, the longer the entire process will be.

A crab of average size can take anywhere between four and eight weeks to go through all the molting stages.

Throughout this duration, it’s completely normal for your crab to stay buried in the sand or substrate.

Hermit Crab Molting Stages

Now that you know that the stages span for quite a long duration, what exactly are the stages of molting for hermit crabs? They’re pre-molt, molt, post-molt, and inter-molt.

In short, a hermit crab spends most of its life in molt phases. So, what exactly happens during each? Let’s dissect them.

Pre-molt phase

Proecdysis, also known as pre-molt, is the phase when the new exoskeleton starts developing below the old one that’s supposed to be shed very soon.

Not only that, but hermit crabs start regenerating lost limbs at this point. In preparation for this, they begin showing limb buds, which are placeholders for the limb that will regrow during molting.

During pre-molt, your hermit crab will store plenty of salts that will help it shed its exoskeleton later on. It will also start storing food and water to help it get through the molting process.

Molting phase

The molting phase is the duration when the hermit crab starts shedding its old exoskeleton and regenerating its limbs. Scientifically, it’s known as the ecdysis phase.

The salts and water that the crab has been stocking up on travel through the hemolymph (crab blood) to the various parts of the exoskeleton. Then, hydrostatic pressure starts building and pushes against the exoskeleton until it cracks under the pressure.

When it does, the hermit crab is able to withdraw from the old shell.

Post-molt phase

The post-molt phase is when your crab comes out looking like it’s gotten a fresh coat of paint. Its new exoskeleton starts becoming harder and the crab starts regaining muscle strength and control.

During this phase, the hermit crab eats the old exoskeleton that it had shed in order to reclaim the nutrients in it. This includes minerals and salts, which help the calcification process that it needs at this time.

Inter-molt phase

This is the phase between one molt and the other, similar to a rest period. Typically, it increases in length the more mature your hermit crab becomes.

This period is rather short for young hermit crabs, as young ones molt a lot more often. Naturally, this is because they grow at a much faster rate.

It’s the longest phase in the cycle. It’s also when the exoskeleton reaches the peak of its hardness after plenty of minerals and calcium deposits.

Do Hermit Crabs Shed Their Skin?

Yes. When hermit crabs molt, they lose almost all of their outer layers. This is including their entire skin. This also includes the coverings on the eyes and gills as well.

Do Hermit Crabs Shed Their Claws?

Yes. After a hermit crab molts, it will shed the shell on its back and all its legs. This includes the claws as well. The point is to regenerate any missing limbs and strengthen existing ones, especially the feeding claw.

Do Hermit Crabs Molt in Their Shell?

The entire molting process doesn’t happen inside the shell, per se. What happens is that the entire outer skin, including the shell, cracks and the crab emerges from the back of its own skin.

Then, the crab leaves the old shell behind, along with the entire exoskeleton. It can return to the original shell, pick a new one, or even take on various items as shell replacements.

What To Do When Hermit Crabs Molt?

The first thing to keep in mind when your hermit crab is molting is that you shouldn’t disturb it.

Some owners will recommend isolating them, and you can do so by preparing an isolation tank. This is important if there are multiple hermit crabs in the same enclosure.

During molting, especially if one hermit crab molts on the surface, the other hermit crabs may attack it or even eat it.

How Do Hermit Crabs Molt?

There are various ways that a hermit crab can molt. It could bury itself in the sand or do a surface molt. Also, it can molt in its shell, which acts as a mold or opt for a smaller shell to bury itself in it without sand coming in.

Whatever the place and behavior your hermit crab chooses to molt in, the process is still the same.

Preparing for the Molt

During the inter-molt period, when the crab is getting ready to molt, it will take in all the calcium it can get in order to send it to the hemolymph.

The parts that connect the crab’s muscles and tissues with its shell will start breaking down when the crab secretes a certain enzyme.

Then, the crab will develop a thin layer that’s flexible under the old shell, which will soon be lost at this point. This thin layer later hardens and replaces the old one.

Filling Up on Water

Around a day before a crab molts, it will fill its body with water. This helps expand the tissues that hold the older shell to the body.

With enough expansion, the old shell cracks at the back, where the crab can come out.

Shedding Old Skin

After the old shell cracks, the crab pushes itself out of that seam. It starts with the back legs, then the front legs, and finally, the claws.

Finally, the crab pulls the lining on the gills and the appendages in the mouth through its mouth. The entire process takes between a couple of minutes to a couple of hours.

The Soft Shell Phase

After getting rid of the old skin, the crab becomes very vulnerable as it’s left with a soft shell. This shell could take anywhere between a couple of days to a few weeks to become hard enough for protection.

This is the phase that keeps the crab buried. They feel vulnerable and exposed to predators, and that’s why they remain hidden until their shells harden.

The Hard Shell Phase

Using the calcium and minerals it stocked up on, the crab starts growing a new shell. Meanwhile, it gives itself room by filling its tissue with water, in order for the new shell to be a bit larger.

Hermit crabs do this in order to bulk up later on.

Bulking Up

This process happens in the inter-molt phase when the hermit crab is getting prepared to go into another molt.

During this period, it eats well and increases its protein intake the closer it gets to the molting phase.

During this phase, it gets rid of the water to make way for the calcium deposits on its exterior as well as for the coverings on the gills to form again.

When Do Hermit Crabs Molt?

A mature hermit crab will molt every year and a half, on average. However, before maturing, hermit crabs can molt a lot more frequently than this.

Medium-sized and maturing crabs will molt around once per year, if not a little more frequently.

Small hermit crabs will usually molt for around two weeks, multiple times per year.

If you’re trying to help your hermit crab to molt, offering it a calcium-filled diet would help induce a molt.

How Do I Know My Hermit Crab Is Going to Molt?

There are some clear signs that a hermit crab is going to undergo a molt. These help you rest assured that your crab is molting or buried, not dead. These signs are as follows:

Firstly, your hermit crab will start eating and drinking a lot more. This is to prepare for the duration when they won’t be able to access food and drink during their molt under the sand or substrate.

Not only that, but the diet will narrow down to proteins and high-energy foods. Besides drinking a lot of water, hermit crabs also like to soak in water or even spill it on the sand before their molts. This is because water facilitates the breaking out of their old skin.

Other signs of an incoming molt include:

  • Excessive digging
  • Less activity and confused or minimal antennae movement
  • Switching to a bigger or smaller shell
  • The exoskeleton looks dull, chalky, or simply discolored
  • Glassy eyes that look like there’s a layer of film on them
  • Having buds where they lost limbs like claws or legs
  • Having a scent that’s close to ammonia

Final Thoughts

Now that you’ve read through the article, we hope the whole topic is clearer to you. While many hermit crab owners can get scared when their crabs prepare for and undergo a molt, once you know the benefits, you’ll be waiting for these molts to happen.

Especially when you keep in mind that this means that your hermit crab is healthy and is maintaining its health and strength.

Share this post: