The Basics:

There are hundreds of species of land-dwelling Hermit Crabs in the world, all-originating from seashore locations in tropical climates. Most specimens available in the retail pet trade are from the Caribbean or Ecuador. Caribbean crabs have rounded
eyes and one front claw that is darker than all the others (giving them their nickname, the Purple Pincher), while Ecuadorian varieties are usually smaller and paler, with oval or
elongated eyes and identically colored claws. Don’t worry about getting “boys” or “girls” – it’s virtually impossible to tell the difference, and hermit crabs only breed in the wild.

Enclosure:
They're Always On The Lookout For A Quick Getaway :

Hermit Crabs are veritable Houdinis, who have a knack for escaping from any enclosure that isn’t secure. They’ve even been known to escape by climbing up the silicone sealant in the corner of glass tanks. So any enclosure must have a secure tight fitting top that also allows plenty of ventilation. They like plenty of things to explore and clamber on, but they also need a sheltered spot to rest - one of the many specially designed coconut shell or wooden hermit hideaways will fit both purposes. Place any tall tank accessories well away from the opening, so the crabs can’t climb up on them to escape. Any enclosure should be large enough to hold all bowls and accessories while still leaving plenty of room for the crabs to run around.

Substrate:
Sand Suits Them Fine:

Not surprisingly since Hermit Crabs live on beaches, sand makes the best substrate. Coarse sand should be avoided, since it can cut into a crab’s tender claws. Fine sand is also inappropriate, since it can clog the gills, so choose a
medium grade. The sand should be twice the height of the largest crab in the enclosure. This will make it easier for the crabs to burrow. If the substrate is spot cleaned daily, it
will only need changing every 2-3 months.

Temperature:
Not Too Hot, Not Too Cold:

A constant temperature of around 72-75º will be most comfortable. This can be maintained by keeping their enclosure in a room with the proper ambient temperature. An under-tank heating pad placed beneath one part of the tank can also be used to create a thermal gradient.

Lighting:
They Like A 12 Hour Photo Period:

Hermit crabs have no special lighting requirements, aside from regular 12-hour day and night periods. Though they’re nocturnal by nature, in captivity they are often active in the daytime provided their lighting is not too harsh.

Diet:
They Are Light Eaters:

Hermit crabs do not have big appetites. They eat very slowly
taking tiny bites, so they should be offered very small portions (a couple of pellets per feeding of commercial dry hermit crab food). This food should form the basis of the diet, together with tidbits of fruit, vegetables, peanut butter, tuna fish or crackers. Since Hermit Crabs are light eaters, don’t be alarmed if their food appears untouched. Remove uneaten food daily, remembering to look for any pieces that may have been hidden away. A small scallop shell can be used instead of a regular food dish - as well as looking decorative and taking up less floor space, it will gradually leach calcium into the food.

Water & Humidity:
They Need It Kept Moist:

Hermit crabs breathe through gills, so moist air is essential to
their health and well-being. If the air becomes too dry, the crabs’ gills will dry out and they’ll die. Gently mist the enclosure with dechlorinated water to keep the humidity at
around 70%, using a hygrometer to monitor the levels. Placing a water bowl over the heated area will also help increase humidity levels. If the enclosure tends to dry out too
quickly, try blocking off some of the ventilation holes or placing a damp towel over part of the lid. Be aware of factors in the room that can lower humidity, such as central
heating. Hermit crabs need two dishes of water, one fresh and one salt. All water must first be dechlorinated, and the salt water prepared by mixing aquarium salt, never table
salt, with the previously dechlorinated water. The dishes need to be shallow enough for the crabs to climb into, but deep enough for the water to come about halfway up the shell.
Put a small piece of sponge in the middle of the dish – this helps prevent drowning and allows the crabs to sip the water more easily. The animals will soak themselves in both
dishes, and may “scoop their poop” into the water, so change it regularly. Replace the sponge frequently, too.