I have 3 hermit crabs and unfortunately, they're like fish...people buy them all the time but don't know how to properly care for them so they die. Hermit crabs do not actually have true lungs. They have I guess what you could consider half lungs half gills. These gills need to stay moist. They're substrate should be sand with enough in the enclosure to cover 1.5 times the size of their shells when they molt. You need 3 extra shells per crabs for shell swapping one should be slightly smaller, one the same size and one slightly larger. Crabs are picky and I bought one crab that changed back and forth between 2 shells about 10 times before he decided to stay with his original shell. Decorations need to be something they can climb on like a rock or a piece of bark as they love to climb. Just make sure it doesn't reach the lid or they'll more than likely get out as they are escape artists. Water. Stressed in the beginning how important water is. Here's what a lot of people don't know: They need BOTH saltwater and fresh water. The water needs to be declorinated just like for your fish but they need a pool of salt and fresh each with a sponge. The salt water is vital for a healthy molt as they will drink a LOT of it right before they shed their exo skeleton. Make sure they have plenty of water on hand. They also need a warm bath in fresh water once a week. Prepare their bath with WARM, not hot water, and place the crabs upside down in the water. This way when they turn over anything stuck in the little crevices in their shells with become dislodged. More on water...you'll need one of those humidity gages for reptiles. It needs to stay in the upper range on a daily basis. I achieve this by misting the sides of the cage every day. Sometimes more. Food: Crabs love a variety. You can offer 3 or 4 different kinds of food every night and then throw it away all except for the hermie pellets which will stay fresh longer and allow them to nibble during the day if they want. Foods Hermies like to eat include (but are not limited to): Tuna, Cheerios (crushed), peeled Grapes, Peanut Butter, cooked veggies, potato chips, saltine crackers, really any kind of fruit, they also like those cans of hermie food...the smellier the better because they are scavengers also any kind of fish will go over well. You will probably hardly ever see them eat and when you go to dump their food out a lot will be left over. Offer small portions, but do change it out everymorning or else the cage will smell. I also crush the pellets because it makes it easier for them to eat. You will need a heating pad made for hermit crabs on one side of the cage. Put it on the outside on either the bottom or the side. I find mine works better on the side due to my crabs are big and I have over 60 pounds of sand in a 20 long and that makes for some deep sand. Cleaning: Purchase a sifter made for cleaning reptile sand. Once a week sift through the sand to rid it of any poop and food you may have missed. Also wipe down the sides of the enclosure with a moist cloth. For the top of the cage you can use a mesh lid, however these usually leave a lot to be desired when it comes to humidity. I purchased a piece of plastic from Lowes that partially covers the top to keep it more humid...something like what it looks like:
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the dotted lines are the mesh lid, the longer lines are the length of the plastic approx. Hope this info helps. Also, don't let them crawl on the carpet as the fibers will irritate their gills. If you let them crawl on the floor, lay down a sheet or similar piece of fabric to make them comfortable. Molting: can't remember how often they do this, but when they do it, don't touch them and leave the skeleton there as they will eat it. Make the environment as moist as possible, but never wet the sand. Remove any other crabs and put them in a temporary cage. Leave all the empty shells for the freshly molted crab and make plenty of water available. Leave the crab alone, cover the sides of the cage and most of the top so it won't become stressed out. Also, you can tell the sex of your crabs by looking under it's legs. Girls have large ovipores located on the first section of two of their legs underneath them. Boys have none present.