Hermit Crab Molting: Everything You Should Know

The most confusing thing for me when I first bought my hermit crab was the molting process. I was unsure if my crab was going through a molt, or just decided to burrow. Even then, I had no clue what to do for my crabs while they molt.

I’ve had hermit crabs for quite some time now, and I’m a bit embarrassed by the staggering amount of information I’ve learned. If you told me a year ago from today that I’d be writing an article teaching people about the hermit crab molting cycle, I’d laugh.  

Anyway, I’ve wanted to create a very beginner-friendly molting guide for owners. I’ve seen other articles that get too sciency and gave me very vague instructions for how to take care of my crabs as they molt. 

To keep things organized, this guide has been broken down into 3 parts: 1) General hermit crab molting knowledge, 2) A breakdown of each stage of the molting cycle and how you should care for your crab at that stage, and finally 3) Signs a molt is going downhill. 

Frequent Molting Q&A

General Hermit Crab Molting Knowledge

In a little bit, I’ll get into each phase of the molting cycle, what your crab is going through, and what you should do for him. Before I can do that, however, I think it’s best if you have a basic understanding of the molting cycle. This section may also answer any questions you might have about your molting crab, so stay tuned.

What is the molting process?

You know how when you outgrow your clothes, you need new ones that fit better? It’s the same for hermit crabs. Their exoskeleton, which is like their protective outer shell, can only stretch so much before it’s just too small for them. So, they have to shed it and grow a new one.

It’s pretty amazing actually, because it allows them to continue growing and developing. Plus, it helps them fix any damage to their exoskeleton, replace any lost or damaged appendages, and become even more mobile and able to defend themselves.

A molt is necessary for a hermit crab’s overall health. It keeps the right balance of ions in their body and making sure their internal organs are working properly. So, you can think of molting as a crab’s version of a growth spurt, but it happens multiple times throughout their life.

What triggers a molt?

A hermit crab molt is triggered by a combination of internal and external factors such as growth, hormonal signals, changes in temperature, humidity, food availability and social cues, among others.

The process is triggered by a combination of internal and external factors. The main internal factor is the crab’s need to grow and replace its exoskeleton as it gets larger. Additionally, internal hormonal signals, such as changes in the levels of ecdysone, a molting hormone, can also trigger molting. External factors that can trigger molting include changes in temperature, humidity, and food availability. For example, hermit crabs typically molt more frequently in warmer, more humid conditions, and when food is more plentiful.

In addition to this, social cues and the presence of other hermit crabs can also trigger a molt. For instance, when a hermit crab is in a group setting and one of its peers starts to molt, it may also trigger a molt for the other crabs in the group.

Molting in hermit crabs is like a caterpillar turning into a butterfly. It’s a natural process that happens so the crab can grow and have a new, bigger shell to live in. Just like a caterpillar’s metamorphosis is triggered by different things like changes in its environment, a hermit crab’s molt is also triggered by a combination of internal and external factors. For example, when the crab gets bigger, when the temperature or humidity changes, or when food is more plentiful. It’s all part of their natural growth process.

How long does it take a hermit crab to molt?

The length of time it takes for a hermit crab to molt can vary depending on a number of factors, including the species of crab, its size, and the conditions under which it is living. Generally, the molting process can take anywhere from a few days to several weeks.

The molting process begins when the crab starts to prepare a new exoskeleton under its old one, this process is called premolt, and it can last from a few days to few weeks, it’s the crab’s way to prepare itself for the upcoming molting process.

After that, the actual molt begins, where the crab sheds its old exoskeleton, this process is called ecdysis, it can take anywhere from a few hours to a full day, where the crab will be vulnerable, and it has to hide itself until the new exoskeleton hardens.

It’s worth noting that after the molt, the crab’s new exoskeleton will be soft and pliable, and it can take several days to several weeks for it to harden and fully protect the crab’s body.

What Does Your Crab Need To Molt?

Hermit crabs need several specific conditions in order to molt successfully. These include:

1. Depth: Hermit crabs need to bury themselves in a substrate in order to molt. My rule of thumb is enough substrate to completely bury the crab and then some. This provides them with a safe, dark, and secure place to shed their old exoskeleton and grow a new one.
2. Darkness: Hermit crabs need to be in a dark environment during the molting process. This is because light can cause stress and disrupt the molting process. As long as they’re burrowed, there is no overhead lamp on your crabs (which there should never be!), and they’re not beside a window, they should be fine.
3. Moisture: Hermit crabs need a high level of humidity in order to molt. This is because their exoskeleton is primarily made of chitin, a protein that requires moisture to harden and form the new exoskeleton. Aim for your tank to be at a minimum of 70% humidity.
4. Heat: Hermit crabs need a warm environment in order to molt. This is because the molting process requires a lot of energy, and a warm environment helps the crab to conserve energy and speed up the process. I recommend reading my article: Keeping Hermit Crabs Warm: Everything You Need To Know for more information.

It’s also worth noting that a healthy diet and a clean environment are also important for hermit crabs during the molting process, as they need to have enough energy and resources to grow a new exoskeleton. Place some egg shells in your food bowl regularly for recently-molted crabs to get the nutrients they need.

Is your crab molting or just burrowed?

It can sometimes be difficult to tell if a hermit crab is molting or just burrowed in its substrate, but there are a few signs that you can look for to help determine which it is:

• Activity level: During molting, hermit crabs will be less active, and will typically remain in their burrow for several days to several weeks. If a crab is just burrowed, it will likely come out of its burrow to move around and explore its environment.
• Exoskeleton: If a hermit crab is molting, you may notice that it has shed its old exoskeleton, which will be visible in or near its burrow. Most crabs end up eating this for its nutrients. I’ve never found an exoskeleton in my tank and I’ve had crabs for 4 years who have molted several times.
• Behavior: If a crab is molting, it will be more reclusive and will spend most of its time buried in its burrow. If a crab is just burrowed, it will be more active and will spend more time out of its burrow.

It’s worth noting that it is normal for hermit crabs to spend time burrowed in their substrate, and they may do so for a variety of reasons, such as to rest, hide from predators, or to regulate their body temperature. But if you notice that a crab has been burrowed for an extended period, it’s probably molting.

A Breakdown of the Molting Cycle

The molting cycle in hermit crabs is a complex process that can be broken down into several stages:

1. Premolt: The crab starts to prepare a new exoskeleton under its old one, this process is called premolt, and it can last from a few days to few weeks. During this stage, the crab may become more reclusive and hide in its shell or burrow in the substrate.
2. Ecdysis: The actual molting process begins, where the crab sheds its old exoskeleton, this process is called ecdysis, it can take anywhere from a few hours to a full day. During this stage, the crab will be vulnerable, and it has to hide itself until the new exoskeleton hardens.
3. Post-molt: After the molt, the crab’s new exoskeleton will be soft and pliable, and it can take several days to several weeks for it to harden and fully protect the crab’s body. During this stage, the crab will spend time in its new shell and may be more active than it was during the premolt and ecdysis stages.
4. Intermolt: This is the period between molts, during this stage the crab will grow and prepare for the next molt. During this stage the crab will be active and eat normally.

Signs Your Crab is About to Molt (Common Behaviors) 

A hermit crab will exhibit several behaviors before it molts. Some of these behaviors include:

1. Premolt behavior: The crab will start to prepare a new exoskeleton under its old one, this process is called premolt, and it can last from a few days to few weeks. During this time, the crab may become more reclusive, hiding in its shell or burrowing in the substrate.
2. Appetite loss: The crab may lose its appetite, it can be because the crab’s body is preparing for the molt and it’s diverting energy to the molting process.
3. Aggressive behavior: A crab may become more aggressive towards other crabs or humans, it can be because the crab is trying to protect itself or its burrow during the molting process.
4. Shell switching behavior: The crab may start to look for a new shell to move into. This behavior is a sign that the crab is preparing for molt, it’s looking for a bigger shell that will fit it better after the molt.
5. Color change: The crab’s color may change as it prepares to molt. The crab’s exoskeleton may appear dull or discolored, this is due to the fact that the crab is producing a new exoskeleton under its old one.

Things to Remember

It’s completely normal for hermit crabs to molt, and it’s important to give them the space and conditions they need to do so safely and successfully. As long as you provide your hermit crabs with the proper environment, including depth, darkness, moisture, and heat, they will be able to molt without any problems. During the molting process, it’s best to leave your hermit crabs alone and not disturb them. Molting can be stressful for the crab and interrupting the process could cause harm to the crab.

If you notice that your hermit crab is molting, it’s best to avoid handling or disturbing it, and to provide it with a clean and safe environment to molt in. You can also provide your crab with extra humidity, by misting the enclosure, to ensure that the new exoskeleton hardens properly.

It’s also important to note that during the molting process, a hermit crab may be more reclusive and less active, which is normal and not a cause for concern. And after the molt, it is important to monitor the crab to make sure it is healthy and able to move around and eat properly.

In summary, hermit crabs will do fine during a molt as long as you provide the right environment and leave them alone. Molting is a normal process in the life of a hermit crab, and it’s important to not disturb them during this process.