Older articles that are no longer in line with current care standards but still have value and should be preserved.

Measuring Hermit Crab Shells

Wee wants to be big so bad

Wee wants to be big so bad

**A newer version of this article is available:

Hermit crab shells sold online are typically sold based on the size of the opening. When purchasing new shells for your hermit crab, measure their existing shell and then choose several shells that are somewhat larger. Hermit crabs typically prefer a shell that fits snugly allowing them to fully seal off the opening to protect themselves from predators and dessication.
The photo shows how to take measurements properly.

Measuring hermit crab shells

Measuring hermit crab shells

Ecuadorian (C. compressus) typically prefer a shell with a D shaped opening and commonly wear shells that are too small.
Other species will wear a variety of shells, both with circular and D shaped openings.


Circular opening shell


D shaped opening shell

D shaped opening shell


My shell is too small!

My shell is too small!


Coenobita cheliped pincer claw

My shell fits just right!


Air Temperature versus Substrate Temperature

UPDATE: Please note that all heat pad, strips should be placed on the back wall of the tank and not under it as used to be the norm.

written by Marie Davis

Check the substrate temperature too!

Check the substrate temperature too!

It can be confusing as to what the temperature of ones Crabitat actually is sometimes.

One buys a thermometer to place on the inside of their Crabitat to monitor the air temperature. The hermit crabs original home is in the tropics, so air temperature of ones Crabitat is important so not to cause them any undo stress. The thermometer is placed at substrate level, along with the humidity gauge, to monitor the temperature and humidity within the tank where the hermit crabs spend the majority of their time.

Even doing this, there are times when some crabber’s experience complications with their hermit crabs. For some unknown reason, they begin to have hermit crabs going shell less within their Crabitat. When asked what the substrate temperature is, they are bewildered. Most have never heard of monitoring the substrate temperature, or even thought to feel the substrate to see just how warm it is. Within the first year of my crabbing, I had discovered during the first cool months that even though the thermometer on the wall of my tank may have read 72 degree’s Fahrenheit, there were times, which the substrate temperature within my Crabitat was actually much higher than what the wall thermometer read. I had found that the substrate temperature was in reality 80 to 80+ degrees Fahrenheit (26.67-26.67+ Celsius) when I took the temperature where my UTH, (under tank heater), was located. I began to take the substrate temperature as frequently as I read the inside wall thermometer for this reason. Frequently, I had found there to be a discrepancy between the two temperature readings. The wall thermometer reading and the actual substrate temperature would vary as much as 5-10 degrees, and sometimes more. During the colder months, the thermometer on the tank wall usually read much lower than what the substrate temperature was.

During the warmer months, the substrate temperature was usually cooler than what the wall thermometer reading was. It seemed as I was continuously taking the temperature of my substrate and needing to plug or unplug the UTH on our tanks according to what the reading of the thermometer was. For this reason, I invested in Electronic Temperature Controllers that had a probe that went into the substrate of my Crabitat. I set the temperature of the Controller to 78 degrees Fahrenheit (25.56 Celsius) to maintain a steady stable temperature within my Crabitat. I would like to take this opportunity to suggest to every crabber that along with monitoring the temperature of the air of their Crabitat, to please also monitor the temperature of their substrate, especially where their UTH or other warming source is located. Substrate temperature is just as relevant as the air temperature within ones Crabitat, especially if one has a hermit crab burrow into it, which they have been known to do.

A hermit crabs natural home is in the tropics. For this reason, they should have a stable air temperature in the Crabitat of 75-82 F degrees. When a hermit crab is subjected to a temperature of 70 degrees F, (21 C) they will begin to go into a hibernation type state. If it is not corrected, this is stressful to the hermit crab, and can eventually be lethal to them. Anything much higher than 85F there is a high chance of them over heating, which can also be lethal to them. Hermit crabs are ectothermic creatures. For this reason, with the warm side of the Crabitat substrate being 75-82 F  there should always be a cooler side as well (72-75F) for the hermit crab to choose where they are most comfortable at to regulate their body temperature.

Global Temperature and Precipitation Maps by Month

Handicapped/limbless/sick Hermit Crab Care

Please read the updated version of this article:

Written by Marie Davis (aka ladybug15057)

Hermit crab dropped leg

Hermit crab dropped leg

During a crabbers crabbing experience one may find themselves faced with a situation of needing to care for a severely handicapped or mutilated hermit crab. Do not despair, it is possible to care for a him so he can regenerate his missing limbs in hopes of having a successful molt. To do so will require extra TLC, time and patience.

First, one needs to have an isolation tank set up. The isolation tank should have a humidity level of 75-80%. (or the same percentage as the main tank humidity level was, unless this hermit crab is new and possibly suffering from PPS, which one would want to adjust the humidity level and temperature of the isolation tank according to the Post Purchase Stress article

Within the isolation tank place a dry sand substrate to limit the possibility of a mold complication in case the hermit crab would have any left over food on his shell or body after feeding. If this is not possible, one can get a small cleaned bowl and place dry sand within it and push this down into the original substrate in the iso, but should be large enough one can place a hut over the bowl. (or get a Tupperware type lid, a clean margarine lid and place dry sand within it) Do not use dry coco fiber, eco earth or a substrate that does require to be used damp so not to pull moisture from the hermit crab. Make a small impression within the sand to place the hermit crab in.

The isolation tank should have a regular night and day cycle up until one notes the gel limbs becoming larger and formed. When this is noted, the handicapped hermit crab should have darkness so his molting hormones can kick in. This can be accomplished by placing cardboard, or a towel on the outside of the tank.

Carefully attempt to offer him a drop of honey which is natures natural antibiotic. Next, with a dropper if possible, gently take the hermit crab and place 1 drop of dechlorinated ocean/sea water with 1 drop of dechlorinated fresh water within his shell. (if the hermit crab is larger, the size of a 50 cent piece place 2 drops of ocean and 2 drops of fresh water within his shell) After placing the drops of water within his shell, carefully place him in the sand impression you made and cover him with the hut. If he had molted, place his exo within the impression in the sand with him. Leave him be to destress for at least 12 hours, or until the next morning.

If he is limbless he will need your assistance in eating, as well as providing him with the water he needs. After permitting him to destress, take part of his exo and crush this into a powder form. Take a drop of 100% pure honey and mix a little of the exo within it to make a mushy paste. (If he hadn’t molted read regarding foods to offer later in this article, also making them into a mushy paste type food) Once the exo/food is prepared have a place ready where you can sit to take the time needed to feed him. Use a toothpick, or something small that you will be able to control easily and place a small drop of the mush on the end of it. Gently and carefully place the food where his maxillipeds (mouthparts) are and wait patiently for him to begin to eat the food. If he shows no interest in the food, you may need to gently touch his maxilliped area with the food to get his interest for him to begin to eat. If you watch closely you should be able to tell when he has had enough to eat, so stop offering the food so not to stress him more than he already is. (this is normally after he has cleaned the toothpick twice from the food you’re offering if he is a smaller hermit crab, if he is a larger hermit crab it maybe after 3-4 offerings) If you have gotten any of the food on his shell, clean this carefully with a Q-tip and ocean water. Once you have cleaned his shell of any possible food, you can place him within the ocean water pond for a minute to see if he can fill his shell with some water.

(make sure he is not totally submerged, and this can vary, if you place him in the fresh water pond for rinsing, place 1 drop of ocean water within his shell when you remove him from the pond, if you place him in the ocean pond, place 1 drop of fresh water within his shell) Once rinsed, place him back within the isolation tank in the area you had prepared for him and place the hut back over him. Please do not disturb this hermit crab again until evening when you have time to attempt to feed him again. The less he is disturbed, the less unnecessary stress he will have to undergo while he feels in such a vulnerable state. For the evening feeding, make a mush out of his exo with dechlor water. For the morning offering you can mix the crushed exo with dechlor water with a little spirulina mixed in as well if you have any. Attempt to rotate this with each feeding until majority of the exo is gone so he hopefully will continue to eat since hermit crabs are known to ignore foods they had eaten within 9-14 hours before.

Once his exo is gone, the feeding must continue on a daily basis in the morning and the evening as well as the cleaning of any excess food off of his shell and the fresh/ocean water dips in the pond. At night prior to you retiring for the day, place 1 drop of ocean and 1 drop of fresh water within his shell so he will have the water he wants/needs.

It is very important to offer him wide varied, high quality diet. Please attempt to stay away from the commercial foods unless they are of higher quality and either freeze dried or dehydrated without any preservatives within them. Offer foods that contain copper, lipids, zeaxanthin, bete carotene, high protein source, a high calcium source, chitin, cellulose, spirulina, seaweed, omega fats, Carbohydrates, etc.

The above care is provided for a hermit crab who has no limbs and not able to move about himself. If your hermit crab has a 2-3 limbs or more, you may wish to alter some of the care advice above. Observe him closely to see if he is able to go to the food dish as well as the water ponds on his own. This can be done too while you are asleep or away by smoothing the sand and checking it for tracks in the sand. If he is able to move about on his own, the detailed care above can be adjusted accordingly.

If you need further assistance, please feel free to complete the Emergency Questionnaire and post it on the forum.

FAQ When do hermit crabs change shells?

Shell Changing Queue - Photo by Brian Hampson

FAQ When do hermit crabs change shells? Shell Changing Queue – Photo by Brian Hampson

**A newer version of this article is available:

Shell Changing Queue - Photo by Brian Hampson

Shell Changing Queue – Photo by Brian Hampson

Note: Fun shell changing videos at the bottom of the post.

crab_crazy asked:

Hi yall! About how often do hermies change there shells? I provide them with shells all the time! Two of my hermies just changed there shell! They look really cute, but, anyway. I was just wondering. Thanks yall!


Hi, Ronni,

Well, there is no exact answer to your question. Some crabs change shells all the time. My Fifi, a PP, after her first molt two months ago, has changed shells at least six times. She went hog-wild after I bought a lot of polished tapestry turbos on eBay.
Most of my crabs have either changed shells after a molt, or, in the case of new additions, immediately upon arrival because the shell they were in was damaged or painted.

Ecuadorians (c. compressus) are notorious for not wanting to switch shells. I had one switch right after I got him because his shell was too small, but of my other three, only one has switched. She has done so twice, again, only after molting. Of the other two, one has molted and has kept his original shell, and the other hasn’t molted yet. I sure wish he would, though, because the shell he’s in is possibly the ugliest shell I’ve ever seen.
Basically crabs will switch when they want to, and there is no hard and fast rule regarding when and how often. All you can do is keep a good supply of crab-friendly shells in your tank in appropriate sizes, and let them do the deed when they want to. Even if they don’t change into shells very often, they will spend a good deal of the time investigating every shell in the tank, whether it fits them or not. It’s one of their forms of entertainment, along with climbing, hiding and foraging. It’s best to keep at least three shells for every crab you have, one slightly smaller, one the same size, and one slightly bigger than the shell each crab is currently wearing, if at all possible. Also, having extras so you can rotate the stock occasionally will keep them more entertained and increase the chances of a switch.


I have a crab, Sabastion (Sab), who is too be for his shell, no matter how hard he trys to hide two or three of his walking legs are parially out, but he refuses to change shells. Any suggestions?


One of my crabbies look like he really needs to change shells but he hasn’t yet. The shell he’s in is looks like its getting too small for him and yet he refuses to change into another one. He’s been in there for a while. I’ve got tons of shells for him and the others to change into. Is this normal? I’ve got all shapes and sizes of shells (all non-painted of course) and different openings. Owning crabbies isn’t as easy as I expected.


There are times this does happen. The crabber thinks the shell isn’t a proper fit, yet the hermie just refuses to change shells regardless of the selections provided. The most one can do is offer a large variety of shells, and if the hermie finds that perfect shell many times they will move when they feel they need to. There are times too that the hermie seems to be a bit stubborn about change, especially if it is an E hermie. Sometimes it does help if one boils the shells to get the scent off of them to encourage the hermie to relook the shells over. By boiling it makes them think it is a new selection of shells. A few crabbers have had some luck by putting the hermie in need into iso with a wide selection of shells to choose from. This might make the hermie a little more secure about changing shells. No need to be concerned over their original shell being shell snatched while shopping.


Before boiling any shells I always let them sit in IO water for about 30 minutes. I’ve just heard too many stories about shells that look empty being , well, not empty. 30 minutes in the water will make even a stubborn crab emerge.
Here’s one of my stubbornest.

Hermit Crab in a Snail Shell

Hermit Crab in a Snail Shell

Hermit Crab in a Snail Shell

Hermit Crab in a Snail Shell

I know you can kind of see him beginning to peek out in the first one because he was getting curious but when he’s fully withdrawn, he’s invisible and because that shell is so light, it doesn’t seem overly heavy when you pick it up.


Fantastic point to bring up LolaGranola! *Clap* There haven’t been many, but have been occasions when hermies have been boiled due to not being able to see them within the shells. There was one that I remember reading that was sadly baked too due to the crabber not seeing the hermie within the hole of a choya log. Sad By the time she heard the clunk in the oven it was too late. Doing a complete ‘head/antenna count’ should be done before boiling or baking.


do they change shells only after a molt? do i need to buy the same shell he has. it looks to be his origanal one. its old looking.


Shell switching isn’t necessarily always tied to moulting. Some will change right away, some prefer to stay in their old shells. If the shell they are in fits and they are comfortable in it, they will stay put until they find one they like better. Some will change for no apparent reason and some will switch often (sometimes several times a day – going back and forth to/from old to new shells). If yours is having trouble fitting into it’s shell when it pulls itself in, you’ll want to supply it with a few more (at least 2-3 to choose from) in bigger sizes. Also, some species tend to be more into shell swapping.

A couple of things to look for…
*Different species have different body shapes so you’ll have to know which you have. If a Purple Pincher, stick with shells that have a more round shaped opening. If a Ruggie, go for more oval or “D” shaped openings.
*For size, it will depend upon how much too small the current shell is, but start with at least an 8th to a 4th of an inch wider than they are currently in when you measure across (side to side) the opening.
*Look for clean, smooth interiors and make sure there is no debris from the previous inhabitant stuck inside. Boil them and shake to listen for anything rattling inside and/or use a small baby bottle brush to clean around the curve inside.
*Look over the outside of the shell too – if there are any holes that will allow water to leak away from the Crab’s body inside the shell, discard the shell or use it somewhere else for decoration. A hole in the shell will allow the crab’s body to dry out or sand and grit to get in, harming your crab. A dry crab can’t breathe properly.
*Painted shells or natural is a personal choice, but most here recommend avoiding painted shells at all costs. Paint can chip off and is toxic to crabs if they eat it. There are tons of beautiful natural shells available that are better for the crab’s health.
*Where to find shells? We each have favorite places to look but Naples Seashell company has been a good choice for us. Their shells are measured for you and I haven’t gotten any yet that were damaged or unsuitable. They have a whole section on just Hermit Crab shells. Other sources if you are willing to go digging, are craft stores. Look for mixed baskets and discard the unsuitable ones – using the good ones. These baskets often come with many shells in them and the oyster or clam shells make nice little treat or feeding dishes. Other tiny shells in the basket can be glued onto containers for decoration.


Nearly all of my PPs, Strawberries, Indos and Ruggies greatly prefer turbos (round openings). The Ecuadorians really like the nerites, whale eyes and babylonia spirata (oval/D-shaped openings). I’ve posted this before, but there’s an eBay store, The Hermit Crab Shack, that has all natural shells at good prices, and Mike that runs it is very good about honoring requests about specific sizes, etc. Some of my crabbies have been in the same shell for nearly two years, and others switch on a regular basis. Happy shopping!


All our species of hermies Straw’s Rugs, Indo’s, and PP’s are in turbo shells too. Majority of our E’s are in turbo’s as well with only a couple who are in the shells with the D opening.

Sara Lewis and Randi Rotjan, New England Aquarium and Tufts University: Hermit Crab Vacancy Chains:

From BBC One: Hermit Crab Housing:

Photos of Coenobita Cavipes lining up for a shell change in Singapore

FAQ How do I choose suitable shells for my hermit crab?

***Note: There is a newer version of this article:

Land Hermit Crab Shell Guide


A hermit crab’s shell is his home and his protection from predators and dessication. Hermit crabs take up residence in discarded shells and can not make their own shell. When kept as pets it is important that you choose suitable shells for your hermit crab.

In semi-terrestrial hermit crabs a well-fitting shell is essential for maintaining low evaporation rates and carrying ample water. An appropriately sized shell in good condition allows invasion of inland environments offering more shade, food and fresh water for C. clypeatus studied on Curacao. Hermit crabs with broken, ill-fitting shells are restricted to the coast, must rely on drinking saltwater, and appear to be in relatively poor condition.[1]

Terrestrial hermit crabs show “shell facilitation”; that is, larger populations of crab generate, through wear, larger numbers of shells suitable for adult crabs. [2]

Hermit crab’s should be allowed to choose the shell they prefer from a selection of different sizes and types of shells. Natural shells are the best option. Painted shells should be avoided. Shells should not have jagged edges or holes in them.

Most species of hermit crabs will prefer a shell with a round opening. Coenobita compressus (Ecquadorian) prefers a shell with a D shaped opening.

Shells should be cleaned and boiled before offering to your hermit crabs. If you collected shells from the beach be sure the shells are EMPTY before bringing them home.

Hermit crabs can be very stubborn about changing shells but do not attempt to force a crab from it’s shell.

Contrary to common belief, a molt does not mandate a shell change! If the existing shell is roomy enough to allow for growth during a molt, the hermit crab may feel no need to change shells. Additionally, you will find some hermit crabs are chronic shell shoppers, always trying on something new.

Hermit crab shells are sold online by the size of opening. To determine the correct opening size measure the opening as shown here:

Measuring hermit crab shells

FAQ How do I choose suitable shells for my hermit crab?

Photos of common hermit crab shells:
Common Hermit Crab Shells

Are hermit crabs looking for lighter and larger shells?
The distribution, abundance and shell selection behavior of three species of hermit crabs
Land Hermit Crabs Use the Smell of Dead Conspecifics to Locate Shells
Coenobita violscens shell behavior
The Social Lives of Hermit Crabs

Check our collection of PDFs for more research documents about coenobita and sea shells.

1. Wilde, 1973
2. Abrams 1978

On molting

Please note this article is old and some of the information may be outdated.

Originally written by Jad Johnson 2003

Perhaps the most traumatic event in the life of your crab, not to mention the trauma for the owner, is a molt. Often for me it begins by checking on my guys in the morning (I find that they like to do it during the night). A momentary flood of panic washes over me when I see crab bits strewn around the Crabarium. “Oh, no. Has he been mutilated, or is he ill?” Then as I realize I have a molter on my hands, I REALLY begin to panic!

Molting (or moulting to our Aussie buddies) is the natural process by which your crab grows. Like all arthropods, they have a hard exoskeleton, or outer shell which does not grow. So about once a year, depending on the size, age, and eating habits of the crab, they will shed their “exo” to complete the growth process. They will also take this opportunity to re-grow any limbs lost or damaged after the previous molt. “But Jad,” you ask, “is there anything I can do to help my little guy out?” I’m glad you asked.

There are some tried and true methods, and then there are more experimental ones. In this article, I’ll deal with standard methods, and will leave cutting edge advances to another day. I will also focus on the above substrate molt. Probably about 95% of my guys molt on the surface. Let’s examine the molting process in segments:

The Pre Molt

If you’re going to help your crab prepare for a molt, you’ll need to know what to look for, right? There are several telltale signs. Some of the more common are: cloudy eyes (like cataracts); slow and lethargic movement; hanging out on the sponge, in the waterdish, or other damp locale; digging in a wetting the sand, and the appearance of gel limbs, if the crab has any missing claws or legs.

Gel limbs are proto-limbs, buds that are the beginning of appendages that were lost previously. They appear well before a molt, but get larger and often darken as the molt nears.
Many land hermit crab owners like to isolate their crabs at these first warning signs. I usually don’t, because when I do, my crabs stay in a little one-gallon critter keeper for three weeks without molting. Of course, when I replace them back in the tank they molt immediately. Usually, I wait until the deed is done before transferring them to an iso tank. My iso tank is about a half-gallon, and I keep it inside my main tank. It is easier to control the humidity and temperature levels this way.

During this pre-molt time, there are a few things you can do to help: Pre-molt baths in water treated with Stress Coat by Aquarium Pharmaceuticals is helpful and practiced by most crabbers. Some more advanced methods include giving your crab honey or Gatorade to give them that little sugar rush to help them increase energy. Some advocate applying natural aloe to parts of their exo. This helps soften the exo.

During the Molt

Not a whole lot to do here. just sit and watch. It is important not to disturb them during the actual even. If possible keep the environment warm, humid, and dark.

Post Molt

Congratulations! The molt is over.. You’re about halfway there. This is often the hardest period for them to get through. If you had just spent several hours sloughing your skin, I bet you’d be exhausted, too! Unfortunately, everything might seem to go right, but the crab still may not make it through this critical time. To help increase your crab’s chances of success, consider these tips:

  • At this point, the crab should definitely be isolated. His soft pink exo is vulnerable to nefarious crustaceans. If you haven’t already done so, GENTLY transfer him to a spare tank, or an iso unit. Some people will take a section of a 2-liter soda bottle with the top and bottom removed to instantly section the crab off with out moving him.
  • Like any other traumatic medical procedure, what the patient needs most is peace and quiet. Try not to handle the crab at this point unless it is absolutely necessary! Too much activity at this point can result in limb damage or loss, and stress to the crab.
  • Be sure to keep the crab’s old exo to munch on. This helps replenish the calcium lost in the molt. I will usually save the uneaten portions of the exo for later molters. If the exo has already been ravaged by Crabarium-mates, then cuttlebone or sterilized eggshells will do.
  • If the iso unit the crab is in is dry, you may want to mist your lil’ guy, because humidity is also important at this time. Remember not to overdo it; a gentle spritz is all it takes. A nearby damp sponge will also help.

After about a week or so, the patient will be ready to rejoin society. Most of the exo will have been consumed; generally the tough leg tips and large feeder claw will be all that remains. At this time your hermit might want to slip into something more comfortable- a bigger shell. Be sure there are several to choose from. Of course, he may like the one he’s already in, thank you very much. They’re so picky about their shells, aren’t they?
For them, it’s exhausting, and for us it’s nerve-wracking. Either way, it ain’t fun. However, your crab’s molt need not be a death sentence. With a little preparation and TLC, both you and your crab will get through it fine. It just takes a little practice and a lot of patience. Pretty soon, you will both be old hats at it. You’ll be calm and reserved. until the next molt begins, then it’s panic city all over again. Oh, Well.

Copyright 2003 Jad Johnson. All Rights Reserved

More articles on molting:
What is molting
Is my hermit crab dead or molting?
Regulation of Crustacean Molting: A Multi-Hormonal System
All about molting by Lisa Loeske
CrabLoverDon on molting