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Introduction

This guide is for purple pincher hermit crabs. Purple pincher crabs are the subspieces I have experience with and they are a very common type of hermit crab sold in many places in the US. Care for purple pinchers and other species is almost identical, aside from a few small differences with their humidity and heat requirements.

The Caribbean hermit crab (Coenobita clypeatus), also known as the soldier crab, West Atlantic crab, tree crab, or purple pincher (due to the distinctive purple claw), is a species of land hermit crab native to the west Atlantic, Bahamas, Belize, southern Florida, Venezuela, the Virgin Islands, and the West Indies. Adults burrow and hide under the roots of large trees, and can be found a considerable distance inland. As with other terrestrial crabs, they use modified gills to breathe air. Their shells help maintain the humidity necessary for gas exchange to function.

Care Overview

Hermit crabs need high humidity, warm air, deep substrate, and pools to submerge in. To properly care for hermit crabs you must have all of these elements. Missing just one of these elements will result in incorrect husbandry and your crab will likely die a slow death.

Hermit crabs can live well over 25 years in captivity and can grow to the size of a softball. They do grow very slowly, but consider their full size when deciding to keep hermit crabs. They will be with you for a long time and get very large, and larger shells are expensive. You will likely need to upgrade their habitat in the future. If you do not think you will be able to care for your crabs in 10, 20, or even 30 years, do not get hermit crabs. However, they are very easy to care for once you have a proper set up.

Where to Find Your Hermit Crabs

All hermit crabs you find in stores are are wild caught. Consider this when buying your hermit crabs. This industry not only takes animals out of the wild, but they also often encourage painted shells which are toxic and sometimes glue the crab to their shell in order to encourage crabs into the painted shells.

The shells are painted before a crab is inside so they use a machine to crack off the crabs current shell and toss them into the painted pile to find a new one. Many die of stress from all of this before they even make it to the pet store.

Breeding hermit crabs is extremely difficult, so it is not practiced to supply pets commercially. You can typically find hermit crabs at many chain pet stores and some small pet stores, and very often in gift shops along the coast.

Hermit crabs are a common pet to be bought for children, who often get bored and parents don’t want to take on the responsibility they thought their 3 year old would like. Check local online groups like Craigslist, Facebook Marketplace, OfferUp, or any other local buy and sell page. You will probably find several postings of hermit crabs plus some supplies for pretty cheap.

Crabitat Supplies

The following is a list of necessary supplies that you will need to start your journey towards hermit crab ownership:

Humidity

Proper humidity is one of the most important aspects of your tank. Hermit crabs have modified gills (not lungs!) that allow them to breathe humid air. Without at least 80% humidity in their tank consistently, your hermit crab will slowly suffocate over the course of a few weeks to a few months. That is no way to live or die and can easily be prevented with a proper set up.

Most of your humidity will come from your substrate, a heat source, and the tank being sealed. Additionally, your pools will help create humidity especially if you install airstones, the same type you would add to an aquarium. Dampening sphagnum moss and adding it to the tank can also help retain humidity and hermit crabs love it! Eco earth can be mixed into the sand to help retain moisture.

Misting should be done rarely if at all. With the right substrate mixture and the rest of the elements in the tank your humidity should stay within the correct range without misting. Daily or frequent misting can flood your tank. The sand will become so damp it no longer retains water and it will pool at the bottom of your tank, slowly building up with nowhere to drain.

If there is a crab trying to molt where a flood is forming it could kill them. Reptile foggers are also a flood risk. Monitor the humidity with a digital hydrometer, an analog one will not give you a correct reading.

If you suspect you might have a flood, you can do a straw test. Take a straw and gently push one end to the bottom of the tank. Cover the top hole with your finger and remove the straw and release your finger to dump the contents into a bowl. If you have a puddle of water in the bowl, you have a flood.

Heating

Your hermit crabs tank should be kept at 80-85F. You want to heat the air not the sand! A heat mat should be attached to the back or sides of the tank above the substrate. Attaching the heating pad under the substrate will cook your crabs if they decide to molt or rest over it.

The heating pad should be labeled for tanks far larger than the one you are using so you can raise the temperature inside high above room temperature. An example would be for a 20 gallon tank, you would want a heating pad rated for a 30 gallon tank or larger. You can also use multiple heating pads. Monitor the temperature with a digital thermometer, an analog one will not give you a correct reading.

You can help your crabitat stay warm by wrapping it in insulation. Reflectix insulation is a good example of something you can use, but you can also simply wrap cardboard in aluminum foil.

Heat lamps are not a good heating option for a crabitat. An LED light to provide a day and night cycle is all you need (light from the room their tank in can also be enough) but a heating lamp will ruin your humidity and create too much heat in one spot. Sealing the tank may also prove difficult with a lamp on top.

Sealing and Insulating the Tank

To retain the humidity and heat you’ve created inside the tank you will need to seal up your tank. Make sure to leave a slight gap somewhere in your seal for air flow, it does not need to be big. If you have air stones in your pools you don’t need to worry about this.

You have a few options for sealing your tank:

Opening the tank 1-2 times daily will give the crabs enough oxygen when the tank is sealed. Although most tanks do well completely sealed, if you find that the glass is collecting condensation you may need to add more ventilation. Too much condensation dripping into the substrate can cause a flood.

Substrate

Material:
Hermit crabs are shore dwellers, sand is what is under their feet most of the time. This is also what they would naturally build molting caves in. Play sand from the hardware store is the only appropriate substrate to use on its own. Eco earth can be mixed in as you like as long as the majority of the substrate is sand. Eco earth helps retain humidity and offers some texture to the substrate.

Do NOT use:

Eco earth on its own is not uncommon in the hobby but is not the best for the crab. This is not what they would molt in when living in the wild. It does not hold its shape or retain humidity as well as play sand and dries quickly. You risk the collapse of tunnels and caves if it becomes too dry, and misting regularly is not advised for any hermit crab tank. Use pure eco earth at your own risk.

Consistency:
Dampen your sand mixture before it goes into the tank with dechlorinated saltwater to help hold its shape. If you are using all purpose sand you may need to give it a rinse and let it dry completely before dampening it again. Mixing it with saltwater replicates the crabs natural habitat and it also helps fight off mold in the future. You want the sand damp enough to hold its shape when you poke your finger into it, but not so wet that it drips when squeezed. ‘Sandcastle consistency’ is what you are going for.

Put the sand in the tank ensuring it is at least 6 inches deep or three times the height of your largest crab through the entire tank. Areas can vary in depth but do not go shallower than 6 inches at any point. The bigger the crab, the deeper the substrate, so you will need to adjust as you see fit for your crabs. If you can make it deeper than 6 inches, do so. They will utilize every inch and you will not have to add more in the near future.

When first setting up your tank your humidity will likely be very high, your hydrometer will probably show your tank reading at 90%-100%. This is normal and will lower after a course of a few weeks. Eventually, the top layer of sand will dry but remain damp underneath, this is what you are aiming for. You should not need to change your substrate ever unless you get some kind of infestation. (I will not cover infestations in this guide because I have not had one).

Why so much substrate?
Hermit crabs will molt every few weeks or months depending on their size (smaller crabs molt more frequently). The crab will dig down into the sand and find a nice place to build a cave, this is why the sand needs to be damp enough to hold its shape.

Once the cave is built, the crab will spend several weeks to months to even over a year shedding its exoskeleton and then eating it to retain nutrients. They will spend more time down below as their new exo hardens up, then they will eventually come back up to the surface. A shell change or even abandoning the old shell under the sand after a molt is not uncommon.

Not providing a proper substrate will cause your crab to attempt to molt on the surface. This will very often kill them if not treated properly, and even when following the emergency protocol, you still have a high chance of losing the crab. Surface molts are very stressful and a sign that something is wrong. There is also a high risk of cannibalism by your other crabs.

Never, ever, dig up a crab. Crabs should only be handled if completely necessary and only if they are already on the surface of the sand. Digging up a molting crab is a death sentence for that crab, even if you don’t think it is molting you should never dig it up.

Pools

You must provide a salt and freshwater pool for your crabs. The container that you use should be deep enough for your largest crab to fully submerge and get in and out of easily. Pools can be as large as you like. Craft mesh is a very common material to use as a ramp in an out of the pool (you can find it at most crafting stores). It can be cut to fit and held down in the pool with rocks. You could also use a large rock in one corner or a stick, but crabs seem to appreciate a smooth incline into the water. If you want a more classy appearance for your tank, you can use aquarium grade silicone and glue pebbles all over the inside as grip.

Hermit crabs drink fresh water and fill the inside of their shell where their abdomen sits with water as well. They usually fill their shells with saltwater, but occasionally will fill up with freshwater. They must be able to fully submerge or they cannot fill their shells, a shallow dish or sponge won't cut it. They fill their shells to keep their bodies and gills from drying out.

Always dechlorinate your water with Seachem Prime dechlorinator as tap water contains chlorine and metals that need to be removed. Prime is very concentrated and just a single drop of it is needed for any pool under a gallon. Hermit crabs can drown so always make sure their way out is stable and is not going to fall over when they climb on it.

Kritter Keepers of any size you choose make great sturdy pools. The extra small size works well for most. You can also use tupperware containers or any plastic container that meets the size requirements for your crabs. You can lower the pools into the substrate or set them on top of it. You can put them next to each other or different spots in the tank.

I found that setting the pools into a larger container makes taking them out for cleaning easier as pictured to the left. Adding bubblers helps up humidity, attracts the crabs, and keeps the water fresh longer. Stagnant water should be changed every 1-2 days where bubbling water can be changed every 3-4 days. A marimo moss ball or two placed into your freshwater can help keep it fresh even longer.

Shells

Purple pinchers prefer turbo shells, but they will sometimes move into other types. Measure the opening of your crabs shell to determine what sizes they will need to upgrade to. Usually the opening is about as large as their crusher claw (the big one). To avoid fights over shells provide each crab with at least five shells of graduating sizes.

Turbo refers to the shape of the shell, they are short, round, with an ‘O’ shaped opening as shown above. It is a good idea to provide mostly turbos (for purple pinchers) with a mixture of other styles of shells as well, each crab has their own preference. If you see your crab in a particular style very often and they seem to prefer it over the turbos, it is a good idea to provide them with more of that type. Some crabs will hold on to one shell for months or years, while others may change weekly or even multiple times a day.

A ‘shell shop’ is an area of your tank where the shells sit in a pile together. Shells can easily become buried and lost, so you can set them in a plastic container to keep them safe. Shower caddies work great for this but any plastic container will do! Before adding your shells for the first time make sure to sterilize them with a boil then rinse them in dechlorinated saltwater. USE CAUTION BOILING SHELLS AFTER YOU PUT THEM IN YOUR TANK!

If you cannot physically count all of your crabs, do not boil your shells. You never know when a crab has switched into a shell and could be hiding deep down inside. A smaller crab in a big shell can make the shell appear empty. Rinsing them in dechlorinated saltwater at any point is fine as it will not harm any hiding crabs.

Never use soap, bleach, or vinegar to clean shells because you will never be able to get it out of the crevices within the shell. Water ONLY. Clean your shells regularly as they will slowly become covered and filled with sand and your crabs may not use them. Rinsing them in saltwater once a month or so is all you need to do.

Naples Seashell Company is a great resource for shells. You can also find them on amazon, etsy, and local fish stores and reptile stores. You can even find bags of seashells at craft stores that may have some shells that fit your crabs. Make sure the shell is not painted or covered in shellac, both are toxic. Polished and carved shells are safe!

Be warned, if you purchase a crab with a painted shell there is a chance the crab has been glued inside because he picked it up while the paint was still wet. Sometimes the crab is able to free themselves, but they will sometimes die because they can’t get out. A hermit crab soaking in their water may help free them from the paint, so ensure they have access to pools. Remove painted shells from the tank when the crab changes out of it.

Handling Your Crab

You should avoid handling your crab as much as you can. Handling them causes a lot of stress, and frequent handling can kill them simply from the stress. They are prey animals and perceive us as a predator. If you need to move or relocate your crab pick them up by their shell to avoid their claws, even small crabs can break skin and their claws are covered in bacteria.

Do not try to pull your crab off decor if they are holding on, they would rather let themselves be ripped in half than let go. Sometimes gently spraying them with water will encourage them to let go.