Tag Archive for crabitat

Airborne Irritants and Hermit Crabs

Hermit crab's gills are sensitive to airborne irritants

Hermit crab’s gills are sensitive to airborne irritants

Land hermit crabs breathe through a modified gill. It is important to protect the gills from strong fragrances, essential oils, candles, household cleaners, chemicals, smoke insecticides and other airborne irritants.

Be mindful of what you spray or use near the crabitat even if your tank is fully sealed. Residual product may still be in the air when you open your tank.

If you are forced to have your home sprayed for insects ensure your tank is fully sealed with saran wrap or something similar. Allow the house to air out at least 24 hours before unsealing your tank.

FAQ-Are there other pets that can live with hermit crabs?

In 2009 we introduced isopods to our crabitats.

In 2009 we introduced isopods to our crabitats.

The list of critters that can safely exist with hermit crabs is fairly short.


Isopods – beneficial tank cleaners
Springtails – beneficial tank cleaners
Food/soil mites – harmless


Fiddler Crabs/Halloween Crabs – aggressive diggers and are likely to eat molting hermit crabs.

Fiddler and Halloween crabs are aggressive diggers

Earth worms, beetles, centipedes, crickets, praying mantis, roaches: May stress each other, over populate, disrupt/harm/ kill/ eat molters. Crabs may harm /kill them. May carry/spread disease/parasites, especially with over population.

Centipedes – venomous
Millipedes – poisonous 

Snails – Hermit crabs can kill snails

Frogs/Lizards – could harm each other, different habitat needs

Fish – inappropriate water for a fish

Coenobita respiration


A hermit crab’s gills are enclosed in the branchial chamber, which functions as a lung. The branchial chamber is on the sides of the thorax, above the crab’s legs. A hermit crab breathes through its gills and branchial chamber, which must be kept moist in order to function. If the branchial chamber and gills dry out, the crab will die. Compared to aquatic crabs, land hermit crab’s gills are reduced in size, and if the adults are kept underwater too long, they will drown. [2]

There are tufts of setae at various sites on the ventral surface that enable moisture from the substrate to be passed to the branchial chamber. [1]

Maintaining the correct relative humidity inside the crabitat is crucial to survival. Without sufficiently humid air your hermit crabs will slowly suffocate and die. Once the gills are damaged from too dry air they can not repair themselves.

Unless you live in a native climate and do not use any form of heat or air conditioning your crabitat will require a lid to maintain the correct humidity levels. Your house is likely 40-50% relative humidity.

A hermit crab requires 70-80% relative humidity. This range is for the purple pincher hermit crab (Coenobita clypeatus) native to Florida and the Caribbean. Other species of land hermit crabs enjoy a slightly higher relative humidity of 85%. You will need a solid lid for the crabitat (tank or aquarium) and a good quality hygrometer and thermometer to accurately measure the air inside of the crabitat.

All hygrometers should be calibrated prior to use.

Different ways to create humidity in your hermit crab habitat.

This tank is set up correctly with solid glass lids.

Humidity levels maintained above 85% are not harmful to the hermit crab directly but can lead to an unsafe environment in the crabitat. Floods, excessive surface mold and mildew, slime mold and bacterial blooms are just of the unsafe conditions that can develop from maintaining excess humidity levels.

Treat your hermit crab in the same manner you would treat a fish and refrain from removing them from their humid environment unless absolutely necessary. A very brief photo from time to time is acceptable. Taking your hermit crab from the tank on a regular basis (for any purpose) is strongly discouraged.

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1. Biology of the Land Crabs Warren W. Burggren and Brain R. McMahon
2. Hermit crabs : everything about anatomy, ecology, purchasing, feeding, housing, behavior, and illness Sue Fox

Central Heating and Air Conditioning

Where is all of the water coming from?

flooded substrate

Photo credit Jeanne Singhass – flooded substrate

A couple years ago when we created our Facebook group to go along with our website I was shocked to find so many people with flooding issues and bacterial blooms in their crabitats. The response to this was a false bottoms.  In 14 years of crab keeping I’ve never encountered this, so it’s on my mind all the time…where is all the water coming from?

I think I may be on the path to the root cause – overly wet substrate at the beginning.

When you take sandcastle wet sand, add wet ecoearth, add bubbler pools and heat and it’s no wonder the humidity in tank skyrockets and stays there. And it’s no wonder the tank floods, all that excess water has to go somewhere after the substrate becomes completely saturated.

When temperatures fluctuate outside of the tank, condensation can occur. Condensation in the tank is going to end up in the substrate, wetting the ecoearth even more. Ecoearth gets warm when it’s wet, have you noticed that? Hot, soggy tank = disaster.

Prior to my house fire I had my 150 gallon set up and had switched from exclusively using overheat lights to using lights with heat pads. I also put in larger pools and one with a filter, in a segmented section of my tank with Growstone around it. This was to monitor for pool leaks but that never occurred.

Before long I could tell my substrate was getting wetter. Algae was beginning to grow on my cork wall divider a few inches below the surface. My humidity was in range but that was likely because I was still using my overhead light hoods at the time and they burn off a lot of humidity.

After the fire I set up my 150 gallon with dry sand. It wasn’t dusty dry but it was pretty close. I chose to use only one thin layer of dry ecoearth and instead added in some coarse chunks of coconut shell. Eco earth was originally added to help the sand retain moisture, now it may be overkill. This decision was based on @Lisa Dawson ’s flood which was trigger by extreme Australian heat causing her tank to overheat and sweat, then the ecoearth got warm and she ended up with a nightmare in her beautiful crabitat. My tank has two LARGE filtered, waterfall pools.

In the photo below you can see how the moisture is creeping down through the layers of sand. I’m sure the sand around the pools is wetter from splashing and minor spills during cleaning.

The tank has been set up about three months now and successful molts are occurring. My humidity is stable, not climbing over 80% unless we have an unusually warm winter day. I will try to take additional photos in the coming months. I don’t know how long it will take the sand to get saturated at the current rate, hopefully never if my humidity stays controlled. After bringing the lights inside the tank my humidity has dropped to the lower end of the safe range at times. I am thinking of bringing the pools up higher when everyone is above ground so that I can add more sand (miscalculation at set up). I will use dry sand again and that should give me some additional information to work with.

So I’m presenting my suggestions for modifications in our instructions for setting up the substrate for further discussion. Those suggestions are as follows.

  • When setting up your tank don’t add water to the sand. My sand felt dry but in reality had enough moisture to pack right out of the bag.
  • Wet sand should be dried before adding to the tank.  
  • Mix up your ecoearth far enough in advance to allow it to dry out completely before mixing into your sand.
  • If you are installing bubbler or filtered pools I don’t think you will ever have to wet the sand. If your humidity comes up to the safe range after a few days, the sand will absorb moisture from the air.
  • If you are using standard pools (deep enough but no bubbler/filter) you might have to lightly mist the top layer of sand to get things going.

Obviously it is much easier to correct a substrate that is too dry than it is to correct a substrate that is too wet. I don’t agree that it is beneficial to the hermit crabs to allow the substrate to become completely saturated.

We have never recommended extremely high humidity. 90%+ humidity coupled with already saturated substrate will result in a tank flood if maintained at that level for too long.

CSJ has also officially changed it’s stance on mixing moss INTO your substrate, read more about that. 

Note: cross posted on my personal blog (All Things Crabby)as well as our Facebook group to encourage discussion.

These ads are served automatically by Amazon. Not all products marketed for hermit crabs are safe for hermit crabs. Please do your research!

DIY crabitat 3D background

by Pam Liberatore


DIY 3D Background

This is my little diy on a 3D crabitat background.  Please remember this is how I did mine and in no way the only way or the correct way.  I really don’t know if there is a right or wrong way.  I think it comes down to what works for you and good planning of the whole process.   I used the instructions at NEherp and studied them over and over again.  

Here is the link: Custom Backgrounds

That being said let’s get started.

Step 1:

First, you need a tank, mine is a 40 gallon breeder tank.  Now I only did one side.  I didn’t think doing the whole back would work for me.  I was worried that there would not be enough heat just from two UTH being placed on the sides.  I chose the left side of the tank because of the angle it will be placed in the living room.

I cleaned all the glass with vinegar water.  First  you apply your silicone, I used black silicone which is nice if are going to use white foam, you will not see the white foam from the outside.

The silicone should be applied thin about ⅛ of an inch.  This helps with the drying time (24 hours). I used a Spackle spatula and some areas I used a gift card to spread it thin.  I applied it in a back and forth motion and then quickly thinned it out with the spatula and or gift card.  This should be done quickly because the silicone will tack up quickly especially if you are working outside on a warm day like I did.  (I also suggest working outside because the silicone does have a strong odor to it.)  Now I did not apply silicone completely to the bottom.  I stopped about 4 inches from the bottom of the tank.  I plan to slope my substrate from 8 inches down to 4 inches near the background.  Don’t worry if you get silicone on places that are unwanted, you can easily be scraped off with a razor blade.

Silicone applied to glass.

Step 2:

Once the silicone was cured I started to layout my ghost wood and cork bark on the silicone.

I did clean all of my cork bark and ghost wood with salt water and baked them at 170 degrees in the oven.  I wanted to make sure my items were clean of any little animals and other things.  For me I just prefer to do this.  Also this is a good time to cut your pieces to get the look and fit you want.

Layout of ghost wood and cork bark.

Layer of Ghost wood and cork bark

Layer of Ghost wood and cork bark

Once I had my pieces placed the way I wanted them I applied silicone to the bottom of each piece.  Now you do not have to do this extra step.  You can simply start applying foam.  I did this because I wanted to make sure each piece was secured before foaming.  First reason is some pieces might be heavy and the silicone is just extra insurance.  I didn’t feel foam would be enough.  Second, I found by siliconing first the pieces won’t move around when foaming.  The foam has some force behind it coming out of the can.  Also please note the green painter’s tape.  This piece would not stand on it’s own while the silicone cured so this held it in position until the silicone cured.  This extra step of siliconing my pieces took another 24 hours before I could move on.  But for me I found it worth the wait.

Step 3:

My next step was applying the foam.  I used Great Stuff for ponds.  It is blackish/brown in color.  I found it online at Home Depot and had it delivered to my local store.  I bought 2 cans, I only used one for the side wall.  And I did use the whole can.

Keep in mind when applying the foam. first it comes out like a rocket and second it expands.  So when I applied the foam near the sides and top I did not apply it against the sides or top, but left about inch because it will expand. Don’t worry how the foam looks after it cures, the fun part is sculpting the foam.

Foam applied

Foam applied - painters tape is used to secure the pieces while the foam is drying

Foam applied – painters tape is used to secure the pieces while the foam is drying

Foam applied - painters tape is used to secure the pieces while the foam is drying

Foam applied – painters tape is used to secure the pieces while the foam is drying

Step 4:

I let my foam cure for 24 hours.  I wanted to make sure the foam was cured all the way thru.  You don’t want to start cutting and find it is still wet in the middle.

It is suggested on the can to use some sort of serrated knife to cut and sculpt the foam. I found using plastic serrated knives worked the best for me.  

This can be time consuming but also I found it fun.  I read somewhere to cut the shiny top part of the foam of so the silicone will stick better, so I did do that.  I used my shop vac to clean up any foam I cut away.

For this part all I can say have fun with it and be prepared to have sore and tired hands.

Sculpting the foam

Sculpting the foam

Sculpting the foam

Step 5:

After I was pleased with my foam sculpting, I started to get ready to lay the silicone down on the foam and apply the eco earth. 

Now it is important to have your eco earth ready to go.  I bought the large bag of loose eco earth.  I poured about half into a 5 gallon bucket.  Next get your latex gloves on, you will need them and if you are like me you will go thru many pairs.  Get your silicone ready.

It is very important to remember that you need to work fast at this part of the project.  Because the silicone will start getting tacky in about 7 to 10 minutes and if that happens the eco earth will not stick.  And if you worked outside on very hot day like I did it will get tacky even faster.  So plan your starting point.

Now before I started I looked over the whole background and decided to start at the bottom of the background first since it is the hardest to reach.  I only applied silicone in small sections and I used my hand to spread the silicone around. (of course with latex gloves on them and mind you I said hand, keep the other one clean to throw the eco earth on with.)  I used a plastic cup and piled it on heavy and gently pressed it down.  I tried to do the nook and crannies first at the bottom of the background.

After I had the eco earth all applied I waited another 24 hours, maybe even more.

Next I gently sat the tank right side up and let the eco earth fall to the bottom of the tank so I could scoop it up with a clean dustpan.  Only a buck at the dollar store and a handy tool to have.

I used a soft utility brush to brush away the eco earth in the cork bark and other places to find any spots I missed. And trust me I missed spots.  So back to the silicone, eco earth and the latex gloves.  This process can take a few tries but it is worth the work and wait.  

Now you are probably asking why didn’t you use the shop vac.  Well I wanted to be able to reuse my eco earth to reapply in spots that needed it. Using a shop vac would not allow the eco earth to stay clean.  Plus I didn’t want to end up sucking off too much eco earth from the background.

Using the brush was time consuming but beneficial.  

Eco earth applied.

Applying the eco earth

Applying the eco earth

Applying the eco earth

Applying the eco earth

It doesn’t look like much now but it will in the next few pictures.

The photographer was crooked not the background LOL!!

I said this before, doesn’t it look like an owl.  If I wanted that look it would of never happen.




Side view of finished background


Another close up view of background

Now that the background is finished I can trim any extra silicone from the glass that I see fit.

This was a fun but involved project.  It took me a lot of time.  I did not want to rush it and I think it paid off in the long run.  

As I said in the beginning this is how I went about it, in no way is this the only or correct way.  I think this kind of project is more of a learning process.  Also it brings out one’s creative side.

I hope this information helps anyone who reads this.  I know it is lengthy, but I wanted to get as much information out there about such a project.  This is something that takes time so don’t rush into it or rush the process.  I hope you have as much fun as I did.

Time: Three Weekends

Materials List:

  • Great Stuff Pond & Stone 2 cans
  • 2 Tubes of ASI Black Silcone
  • Putty Knifes
  • Ghost Wood Pieces—Small
  • Caulk Gun
  • Cork Flats
  • Small Cork Tubes
  • Misc. Plastic Knives for carving foam

Buy a Vivarium Custom Background Kit based on the size of crabitat you have. NE Herp makes this so easy!!

Vivarium Custom Background Kits from NEHerp

Vivarium Custom Background Kits from NEHerp

Getting Rid of Ants in Your Crabitat

ant3If you’ve ever dealt with ants in your home you know what a challenge it can be to get rid of them. Ants in your home may be a nuisance to you but ants in your hermit crabs’s home can be dangerous. Ants can and will attack molting crabs, and this could kill the hermit crab. If you find ants in your crabitat it is an emergency situation that must be dealt with immediately.


Your approach will depend on the answers to a few questions:

Where are they coming from?

Are they coming into the crabitat from outside or are they living in the crabitat?

What are they doing in the crabitat? Are they coming in for food and leaving or are they building a nest?

How are they getting in the crabitat? Are the climbing up from the floor or dropping down from above?

If the ants are building a nest in the crabitat this is the most critical scenario.

If you have determined that the ants have set up residence in your crabitat you will need to tear down the tank. Set up a temporary tank in a plastic bin as seen here. Emergency Temporary Housing for Hermit Crabs but with one alteration: very shallow substrate!

If you have molters down, they must be dug up. Yes this may kill them but the danger from the ants is greater. Remove your substrate as carefully as you can until all of your hermit crabs are located.

I would suggest a gentle bath in dechlorinated ocean water to ensure no ants are inside of your hermit crabs shells. The ocean water should repel them. Freshly molted crabs can’t be bathed. Place all of your hermit crabs into bin while you clean the crabitat. I would recommend leaving your crabs in the bin for at least a week to keep an eye out for more ants. Monitor your molters closely for signs of distress. Any crabs that go naked should be offered safe shells (that weren’t previously in the tank if possible) and their old shell boiled in case there are ants or eggs inside.

In addition to the live ants we have to address the eggs, which are incredibly hard to destroy. Nothing from the main tank should be reused in the emergency tank at this stage. Any wood items in the tank should be replaced completely in case they are infested. Plastic items can be cleaned in your dish washer on the hottest and longest cycle and once fully inspected can be reused. Throw away all substrate, cocofiber decor, cocohuts, fake plants and any other that could have ant eggs clinging to it. Boiling water seems to be a common method to kill the eggs. If you have the equipment to boil your decorations you may be able to save them. Do not attempt to save your substrate, sand is super cheap. Do not attempt to save any wood pieces. All empty shells should be boiled for a long time.  You may also want to place them in a zip lock bag or air tight bowl for up to 12 weeks. Ideally you have some spare shells that weren’t in the tank and aren’t suspect and can be offered.

Once your crabitat is empty it will need to be thoroughly cleaned before setting it up again with new substrate. You can use a mix of straight apple cider vinegar and lemon juice to clean the crabitat. Let it dry and air out. I would clean your lid as well. Additionally I would follow the steps below for destroying the scent trail. Ants that are gone from the nest when you tear the crabitat down will follow their scent trail back to the crabitat.

If the ants are coming in for free food we need to prevent access and discourage their return.

Ants leave a scent trail so that their nest mates can find the nest and sources of food. You must destroy as much of the scent trail as possible. One safe method would be to mix vinegar and lemon juice in a spray bottle and use it to wipe down anything and everything near your crabitat. A drop of dish soap may help as well. If you have hardwood or other non carpet type floors, mop all around the crabitat and then work your way out. Do as much of the floor as you can, especially if you don’t know where they are coming in.  If you have carpet you can sprinkle baking soda all over. Again start at the crabitat and work your way out. Don’t vacuum it up until you have been ant free for several days. Don’t forget to consider the ceiling as a route of entry, this is a confirmed method of entry for determined ants.

Once the scent trail is destroyed, put a thick barrier of Vaseline around the base of your tank, then around the top near the lid. It needs to be thick and wide enough so the ants won’t cross it. If you have airlines or power cords going into your crabitat they should be protected with vaseline at the point where touch the tank. If possible don’t allow them to drape down providing an easy path into the crabitat. Next you can lightly crumble whole bay leaves and sprinkle them around your crabitat. If your tank is on a stand, you can place them on the floor around the base of the stand.

It may be helpful to only feed dry (boring!) foods to the hermit crabs for a few days and avoid strong smelling and sweet foods.

Some people have good luck protecting their house from ants by spreading Borax in their doorways to the outside.


Setting up a proper crabitat

Let’s look at how to set up a proper hermit crab habitat, which we refer to as a crabitat.

Basing your tank set up on what you saw at the petstore or mall cart where you may have purchased your hermit crabs is a recipe for disaster. Kritter Keepers and wire cages are death boxes and should never be used.

Listed below are the primary components of a proper set up and we will discuss them in detail. If you are not willing to equip the tank properly you should return your hermit crabs or rehome them, they will not thrive without a properly set up habitat. Captive hermit crabs can live over 30 years in the proper habitat. Most hermit crabs die either in the first month of ownership, during the first molt of ownership or within the first year to 18 months.  So yes, they can technically ‘survive’ in poor conditions but why on earth would you purposely do this to an animal???

A simple list of the items you will need to properly outfit the crabitat. There are low cost options for most of these items.

  • Tank
  • Lid
  • Light*
  • Heat
  • Substrate
  • Gauges
  • Bowls
  • Climbers
  • Hiders
  • Plants and Vines

The tank itself should be glass or lexan and large enough to comfortably house your hermit crabs. A MINIMUM of 2 gallons of space per small or medium hermit crab but 5 gallons per crab is much more humane. Large and jumbo crabs will need much more space, 10 gallon minimum. A 10 gallon tank is too small for even one large or jumbo crab. Plan for the future when purchasing your tank, allow for the growth of your crabs or additions to the herd.   A used tank is perfectly fine and will greatly reduce the cost of supplies.

The tank must have a lid that retains humidity. A screen lid with glass, lexan or plastic wrap on top is what is typically used. Hermit crabs require humidity to breathe. Opening the lid for feedings and water changes each day usually provides enough air exchange. Fresh air flow reduces mold, mildew and fungus growth.

Light is required, whether they are used as your heat source or not. Hermit crabs require a normal 12 hour cycle of light and dark, it is vital to the molt process. If your crabitat is in a well light room that will meet the need of daytime light. Do NOT place your tank in directly sunlight!

UVB is believed to extend the life span of captive hermit crabs. UVB bulbs must be mounted in such a way that there is no glass or plastic barrier between the bulb and the hermit crabs. Most people mount the lid inside the tank.  Bulbs must be replaced every 12 months.

For nighttime viewing, LED in red or blue is safe. Your hermit crabs do not require a light at night.

Hermit crabs require warm temperatures. This can come from overhead lights or from heat pad (often called under the tank heater or UTH) which is placed on the wall of the tank and not under it. Over head lights or heat emitters are not recommended for inexperienced pet owners. They make it challenging to maintain the correct environment in the tank.

Ways to heat your crabitat

Global Temperature and Precipitation Maps by Month

Gauges are the only way to monitor and maintain proper heat and humidity levels. The tank temperatures should be a range of 75F to 82F.  72F is the absolute minimum and your tank should not remain at this temperature long term. A temporary dip or spike in temperature is not cause for concern. A range means that your tank should have areas of different temperatures. Some species seem to enjoy slightly warmer temperatures but the common clypeatus is happy in the 75-82F range. Check the substrate temperature as well to make sure it is not too hot. Overly warm substrate will kill molters or discourage molting. Humidity ranges should be 70-80% this is relative humidity. Occasional higher humidity is not cause for concern but maintaining excessively high humidity could lead to flooding or lethal bacteria due to over saturation of your substrate. Your analog hygrometer will need to be calibrated before use. Wireless, digital gauges are relatively cheap and are more accurate than analog gauges.

Substrate should be a mix of 5 parts play sand and 1 part eco earth. The ideal mix will keep the sand moist throughout. The consistency should be so that you could easily make a sand castle. That means that molting burrows will not collapse from drying out. We suggest using a brackish water to expand the eco earth bricks. This will help reduce the chance of mold. The eco earth should be DRY when mixed into the sand so you don’t end up with water logged substrate at the beginning. You can always add water once the crabitat environment is stable, if needed. In many cases it is not needed. Starting with too wet substrate will lead to flooding and/or bacterial blooms.

The eco earth will help maintain humidity but you may need to add some moss pits if your levels are too low. Not all moss is safe so be sure to check our list: Which types of moss are safe for my hermit crabs?

Substrates for hermit crabs

Three bowls will be needed. Two of the bowls should be deep enough to allow your hermit crabs to submerge themselves. One should be fresh water and one should be ocean water made with marine grade salt mix. All water that comes in contact with your hermit crabs must be treated to remove chlorine, chloramines, ammonia as well as other chemicals. The third bowl will be for food. These don’t have to be reptile dishes specifically but they should be something that your smallest crabs can easily enter and exit. Many people use disposable Gladware type bowls for water pools. We recommend placing a rock, fake plant or coral in the pool for the smaller crabs to climb out.

Places to hide, things to climb on, as well as plants and vines are important to create an environment that is stimulating and enriching for your hermit crabs. Huts do not have to be made of coconut shells, many things will work. The same holds true for things to climb on. There are lots of DIY ideas or less expensive ideas for creating vertical climbing opportunities. Fake plants and vines from a craft store will work as well as the ones you find at the pet store. Some live plants are safe for the crabitat but your hermit crabs will most likely kill them.

Creating additional levels in your crabitat to maximize usable space

Your goal should be to create an environment that is as close to what hermit crabs experience in nature as possible. Hermit crabs live primarily on beaches, so think tropical!

Here are some examples of properly set up crabitats:

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Ask Milo – Brown beetles in the crabitat

Alison asks:

I have small brown beetles in my crab cage. They are not on the crabs and they are not mites. They move very fast and hide under the bowls and there are dozens and dozens of them that come out at night to eat crab food. I suspect they may have hatched from some of my high-end crab food. Any ideas for getting rid of them short of dumping the entire sand/sphagnum substrate (very large cage with six inches of substrate…weighs about 75 pounds so hard to deal with.)

Hi Alison!

It’s difficult to know what kind of bugs you are dealing with without seeing a photo. We have a couple articles that might help:
Household mites and bugs

Guide to bugs you might find in your crabitat

Ask Milo – What size tank do I need?

Mattiesse ask:

I am the proud owner of 4 beautiful crabs in Brisbane. the problem is, is that I live in NSW so my other parents in queens land need to take care of them. luckily im bringing them down here but I cant bring the tank, so im gonna have to make a new home. im planning on getting more hermit crabs as well so I need to know how to make the best sized and equipt tank for soon to have not 4 but 6-8 hermit crabs. how big should the tank be and what is the best stuff to get for them so they live a long healthy life!!!

How exciting! The amount of space you need depends on the size of crabs and the number of crabs. Long term you should have 10 gallons of space per crab so you would need at least an 80 gallon tank if you are going to keep 8 hermit crabs. That will give them plenty of space in your crabitat as they grow. You will need a lid that can hold in the humidity, a proper heat source, a day time light and about 12 inches deep substrate (mix of play sand with a bit of cocofiber mixed in). Also food dishes, saltwater and fresh water ponds (deep enough to submerge in), gauges, places to hide and things to climb. Oh and yes a bunch of shells!

For more details check out some of our articles:
Hermit Crab Essentials Shopping List
Newbies Guide to Hermit Crabs