Hermit crabs don't need an elaborate home, but the appropriate temperature and humidity are vital to their health. Land hermit crabs come from warm tropical climates and, therefore, they need a warm, humid environment to survive.
Picking the Tank
Hermit crabs will feel at home in either a glass or plastic tank. Choose a 10-gallon aquarium with a lid. A sliding glass one will work well to contain humidity. The small plastic homes with accessories sold as hermit crab kits are too small, though these plastic cages make excellent temporary homes or isolation tanks. Despite their name, hermits are quite social and are best kept in groups.
Sand is the substrate of choice for hermit crabs because they like to burrow down into it. Playground sand, which can be found at home improvement stores, works well and is inexpensive, though aquarium sand is fine as well. You may want to rinse, dry, and bake the sand (at 300 degrees Fahrenheit) to sterilize it, and it can be rewashed and used again. Calcium-based sands are nice and come in a wide array of colors but are expensive.
Other options include fiber bedding made for reptiles such as the coconut fiber-based bedding called Forest Bedding. The fiber is ground quite fine and is nearly like soil, so it is good for burrowing. Crushed coral is also a nice choice, but you may want to provide an area with Forest Bedding or sand as your hermit crabs may prefer these substrates for molting. Avoid the use of gravel or wood shavings.
Maintaining Proper Temperature
Hermit crabs are happiest kept at 72 to 80 degrees Fahrenheit (22 to 27 degrees Celsius). If the temperature drops below 72 degrees Fahrenheit regularly, the crabs will likely become weak, stressed, and ill. Unless you live in a tropical climate, you will need to use a heater at least part of the time to keep the crab tank at optimal temperatures. Undertank heaters (UTHs), lights, or a combination of both can be used to maintain appropriate temperatures.
The UTHs can be placed under one end of the tank to provide a warm side and a cooler side. These will raise the temperature a few degrees above room temperature. For ideal temperature control, these can be combined with a thermostat to maintain a given temperature, or you can put them on a timer to come on and off to maintain temperatures. Invest in a good thermometer for inside the tank, and monitor the temperature near the substrate. If the heater isn't heating the tank enough, try removing some of the substrates over the heater—the thinner substrate will increase the heat in the tank. If the tank is getting too warm, you can increase the depth of the substrate. Some experimentation may be necessary to get good, stable temperatures. Make sure that there is a temperature gradient in the tank, so the crabs have a choice of temperatures.
Lights of various types can also provide heat for the tank; some experimentation with lighting may also be necessary to find the combination of lights and UTH that works best for your tank.
In the past, it was thought that hermit crabs were nocturnal and that providing lights could be stressful for the crabs. However, low-wattage and special night light bulbs are a good option, and many crab owners have found their crabs became more active with lighting and even bask near the lights when the lighting was added to the tank. Be sure to provide a light-dark cycle, such as 12 hours of light and 12 hours of dark. This means day-glow or fluorescent bulbs should only be off at night, though special nighttime bulbs can be used if desired. Using a desk lamp to heat the tank, or high-wattage reptile bulbs, may overheat the tank and be too drying, so these are not recommended.
The easiest way to add lighting is to use a reptile heating/lighting hood over the tank. Hoods can be found with two ceramic receptacles for incandescent bulbs; a day-glow bulb can be put on one side and a night glow bulb in the other. It is best to start with 15-watt bulbs and go to higher wattages only if necessary, especially with a 10-gallon tank. If necessary, wood slats can be used to raise the hood a bit above the glass if it gets too hot. Some hoods have a third receptacle for a fluorescent bulb, and some owners have reported good results with a Reptisun 2.0 fluorescent. Reptile heat hoods are best used on glass top tanks or screens, though screen tops make humidity regulation difficult, as the lights will be quite warm and could melt the plastic. A combination of lighting and undertank heat can be used to heat the tank.
Along with the proper temperature, adequate humidity in the tank is vitally important to hermit crabs. Because crabs "breathe" via gills, the proper exchange of oxygen by the crabs depends on the humidity in the air. If the tank air is too dry, the crabs will essentially suffocate. They need a relative humidity of around 70 to 80 percent. Because this is so important to the crabs, it is worth investing in a humidity meter, known as a hygrometer, which you can find in the reptile section of the pet store. Excess humidity is not desirable either as it will cause condensation as well as encouraging the growth of bacteria and fungus in the tank.
The water dish you provide in the tank will likely be sufficient for creating the proper humidity, as long as the tank is enclosed with solid sides and top. If you need to increase the humidity level, try a fairly large chunk of a natural sea sponge in a dish of water (remember to always use dechlorinated water). The sponge can hold lots of water and has lots of surface for evaporation to boost the humidity. Have a couple of sponges on hand so you can swap and clean them frequently (soak them in very hot dechlorinated water or a sea salt/water mix, then allow them to dry completely as they are a good medium for bacterial growth). If a mesh or vented lid is making humidity control difficult, the lid can be modified by covering most of the top with plastic wrap or clear packing tape.
There are three necessities for furnishing the cage: stuff to climb on, a water bowl, and food dish.
- Climbing: Land hermit crabs love to climb, and this is a good way to provide some exercise. Choya (or cholla) wood is ideal and can be arranged to allow climbing. Pieces of coral, driftwood, and other types of wood can be used—the reptile section of the pet store is a good place to look for a variety or check the online hermit crab retailers listed below. Artificial plants are also a great addition to the crab tank. Periodically change things around or add different items to provide some variety and interest for the crabs. Some enterprising individuals even use Legos to build climbing structures for their crabs.
- Water: Hermit crabs should have access to both fresh and saltwater, so you will need two water dishes. They should be big and deep enough to let the crabs get into them if they wish to soak—especially the saltwater dish—but easy to get out of and not so deep that drowning is a risk. Strawberry hermit crabs should be given a salt pool deep enough to fully submerge themselves in, but for most species, it does not need to be that deep. With deeper dishes, smooth river stones or pieces of coral can be used as ramps or steps for the crabs to get out of the water. You should also place natural sea sponges in the water dishes; some crabs will press on these to get water to drink, and they help regulate the humidity. All water given to the hermit crabs or used in the tank should be dechlorinated (the drops available at pet stores). Saltwater should be prepared using a marine aquarium salt such as an instant ocean (mix as for saltwater tanks), not the salt made for freshwater tanks and never table salt.
- Food: For food dishes, you will want something shallow, sturdy, and easy-to-clean. Flattened heavy plastic dishes made to look like rocks can be found in the reptile section, or you can use shallow ceramic dishes made for small animals. Some people also use natural sea shells for feeding.