Skip to main content

How to Care for a Molting Hermit Crab

  • Author:
  • Updated date:

Finatics enjoys writing about animal care and is "owned" by a guinea pig, four hermit crabs, three African dwarf frogs, and a betta fish.

What Should I Do if My Hermit Crab Is Molting?

While it's molting, what a hermit crab needs is isolation. Although hermit crabs only molt about once every 18 months, if you don’t know what to do when the time comes, it can be very stressful for you and your crabs. Many people suggest making an isolation tank as some crabs may attack the molting one. More importantly, you need to recognize the signs that a hermit crab is molting before you can isolate them.

Signs That Your Hermit Crab Is Molting

  • Your crab suddenly starts digging, although this can be caused if the humidity and temperature are not at the right levels. A crab might dig deeper to insulate himself from conditions he does not like. If it is a crab newly bought, it could be due to stress and a new habitat.
  • Your crab eats and drinks excessively. This is because he’s storing fat and water in a small, gray-black “bubble” on the left side of his abdomen.
  • Lethargy, less activity
  • An ashy exoskeleton
  • Dull, cloudy eyes
  • The crab replaces a missing limb with a gel limb, which looks like a little nub where their leg should be.
  • Antennas look tangled and show less activity.

Setting Up an Isolation Tank

There are three different options for isolating your hermit crab:

  1. Buy another small glass or plastic tank, as long as you can provide the right amount of humidity and heat.
  2. If your tank is big enough, you can put a small tank inside the main one, so the temperature and humidity remain the same.
  3. Isolate your crab in the main tank.

Option 1: Buy Another Tank

The first option is probably the most expensive, but it guarantees that other crabs will not attack the “molter.” When hermit crabs molt, they are inactive, so they don’t need a very big tank, though it must be large enough to hold a water dish and a food dish. A small one will do—molting is a serious affair! They’re not there to play around, so you do not need to worry about decorating it with things to climb on.

Fill a dish with their regular drinking water. If you want, you can even fill one with saline water since molters need salt to help retain water. Their food dish should have food packed with calcium in it, such as cuttlebone, sand dollars, boiled eggshells, and sea biscuits.

Around six inches of moist substrate should be in the isolation tank so the molter can bury itself. You’ll need to purchase a pet heating pad (unless you already have one) to keep the temperature around 78-80°F and humidity around 78-80% since moisture is essential to molting. To keep an eye on the temperature, a hygrometer and thermometer are also recommended.

You can also add large shells to the isolation tank. And although this isn’t necessary, depending on when you put them in there, the crab might not have enough time to dig in the sand, so they will dive in the large shell and molt there. Darkness is important to molting; studies have shown hermit crabs have healthier molts in darkness, like when they’re under the substrate.

Option 2: Put a Tank Inside the Main One

The second option also requires another tank, but without another heating pad and other additional supplies. Fill it with substrate, a water dish and food dish, but you don’t need to worry about the humidity or temperature, since it’s inside the main tank!

Lastly, you can isolate your hermit crab inside the main tank. Some people suggest using the side of a bottle of soda to stick inside the sand. As long as it keeps the molting crab isolated from the other crabs, you don’t need to be concerned about humidity or temperature (unless it’s not right in the main tank!). Just make sure that the other crabs cannot climb over the barrier; otherwise it’s useless.

Option 3: Isolate Your Crab in the Main Tank

Many people argue it’s best to keep molters isolated, but others disagree. They say hermit crabs should be kept in conditions that stimulate their natural environment—and in the wild, hermit crabs bury themselves for protection against other crabs as well as for darkness. Some also argue that isolation tanks bring unnecessary stress and deep substrate should be enough for the crabs.

Whatever you decide to do, this crab should be provided with peace and quiet so he can molt without getting stressed out.

Provide Privacy for Your Hermit Crab

If you suspect your hermit crab is preparing to molt, dig a small hole as big as the crab in the isolation tank and leave him there. Check again in half an hour. If he was serious about molting, he would have dug underneath the substrate already.

When your crab is molting, the best thing you can do is leave him alone. Resist the urge to take a sneak peek at him; you don’t want to stress him out or tear his soft, new exoskeleton. The most you should do is mist the tank every day and replace the food and water. Hermit crabs molt all the time in the wild, so they know what to do. If, for some reason, you absolutely must move him somewhere else, use a spoon to gently move him to a new place.

How Long Does a Hermit Crab Molt?

Hermit crabs can take several weeks to a month to molt, but wait until your crab acts like himself again, is more active, and has eaten his old exoskeleton (it has plenty of nutrients!) before moving him to the main tank. Molting is how hermit crabs grow; they shed their hard outer-casing and grow a bigger one.

Additional Resources

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.


Fern on August 05, 2020:

Natey wtf that is animal abuse and many people would have taken those hermit crabs from u gladly for like 20 bucks each. And also how is hurting and killing animals funny. WTF really. You should really talk to someone about how you thought killing these poor hermit crabs was fun. I have hermit crabs and if you take care of them properly they turn into very nice looking animals. They are also very nice if you give them the proper training. I even taught mine a few tricks like going through a small hoop and grabbing a small stick if I say hold it. They are very intelligent and it is sad that you killed them. I hope u know what you did was wrong now and that many people love these guys as pets.

natey on July 25, 2020:

i don't like hermit crabs cuz they are ugly and i killed some unwanted hermit crabs by dumping them on a hot asphalt drive way and then stomping on them grinding them under my Bluntstones...not the most humane but fun and funny! i showed them im the boss! ^_^

Stephanielewis5161983 on June 28, 2020:

My hermit crawled face first into another shell and hasn't moved is he molting ? Should I cover him ? Help

Tiffany on May 10, 2018:

Please I need help! My crab just molted but I don’t have a shell for it!!!

derek on February 09, 2013:

thanks for the news

.I almost thoght that my hermit crab died!

Angel on November 13, 2012:

My crab digs a lot but i don't know if it is molting or the temp because the temp isn't perfect. I just can't tell, HELP?!?

Tessa toutant on July 29, 2012:

I have an odd problem I have two crabs molting at the same time adthey are in the main tank and the other crabs I put in the other tank I seperTed the two molting crabs by a piece of cardboard is that ok it's my first time ever having a crab molt please I need help

Me on May 02, 2012:


RalphGreene on September 14, 2011:

I really appreciate this hub, I enjoyed to read it.