First of all, a little ground information. Humidity is how moisture is evaporated into the air. Very dry air has a low humidity. Very moist air has a high humidity. Although hermit crabs have adapted to live on land, they do have gills. These gills are different from gills of any fish or marine creature of some sort. These gills are smaller and hardened and basically modified to breath moist air. Typical house humidity is 40% - 50%. Take a deep breath, does the air feel somewhat moist? Well if it does then that's nothing compared to what hermit crabs need. Hermit crabs in captivity do well with humidity from around 77% - 87%. Although the tank really can't be "too humid" that the crabs have trouble breathing, an extremely humid tank will cause bacteria to easily build up in your tank.
In your tank, buy a hygrometer (also called hydrometer or simply humidity gauge). Whether its a stick on or fancy digital hygrometer, it is vital to accurately determining the humidity. You should also be aware that there are gauges that measure humidity and gauges that measure relative humidity yours probably measures relative humidity. That is what we use to measure. So get one that measures relative humidity. Most gauges at pet stores measure relative humidity, while ones for gardens and cigar keepers may measure exact humidity.
Anyways, for a stick on gauge, keep it as close to the centre of the tank as possible and keep it near the substrate. Make sure the surface is clean and dry when placing it on the glass. With digital gauges, keep the probe near the substrate at the centre as well.
Now for the good stuff. How to keep it humid. Well from my knowledge it goes (from best to worse):
1. Keep the substrate moist. Poke a hole in the sand or coconut fiber and see if you can make a hole without much effort. The substrate should be sand castle consistency. Not dry, not dripping, but relatively wet. Every week or so check to see how moist it is, if its to dry, dump some water into the four corners of the tank very slowly. Don't dump water where a molter has buried, when crabs are molting, it is always a good idea just to mist the substrate rather than drenching it.
2. Have a good lid. A sheet of glass or Plexiglas with some air holes is your best bet. When using heat lights, you should use a screen lid with a full sheet of glass or Plexiglas with a circle cut to fit the diameter of the lamp. Then cut air holes and your good to go. The reason the lid should be like this is because if the tank is closed off as much as possible, not as much humidity can escape. This also prevents crabs from escaping, which believe me, they will try.
3. Mist the tank. Get a large spray bottle that mists, not squirts. Fill with hermie safe water and mist all the sides of the tank, the bottom of the lid, and the substrate. Never mist your crabs themselves. This can stress them out. About once a week, what I like to do is spray everything in the tank like the plants, branches, and shells. This makes it look like it has rained. In the wild, hermit crabs usually come out when it is raining or after is has rained. They usually come out after I do this, especially in the evening.
4. Keep the water bowls full. A primary fact to a humid tank is an evaporative water source. The main one is the substrate, the secondary one is the dishes. This is especially effective when using heat lights.
5. Create moss pits. The crabs like digging and grazing in moss piles. If they are damp they will create an excellent source of moisture. They will keep the tank humid enough to not have to spray the tank as much. Moss does not need to be replaced or cleaned. Just creates pits and piles and keep em wet and that's it.
6. Create this humidifier I thought of. WARNING: this only works with heat lights. Take a small bowl and fill with water, then wrap tightly with saran wrap and poke a hole in the top. Place on the hot side of the tank and voila. Make sure the crabs cannot get in it.
7. Use sponges. I don't really like using sponges, but they can keep the tank humid. When using them, have at least two. Keep them in the water dish, don't dampen them then place on the substrate as they will easily dry out quickly. Placing them in a water dish keeps the wet quite long, and it also helps small crabs get out of the dish. Some crabs even use the sponges as water source themselves. BUT: When using sponges exchange with another sponge every week. Sponges can cause quick bacteria growth and can harm the crabs if not cleaned every week. So once a week place a dry, clean sponge where the old one was than dry out the old one completely and microwave for 20 seconds. This is why I don't like using sponges.
And there you have it. 7 easy ways to keep the tank humid. If you have any other ideas, please post them here. Also please share any positive feedback you have. Thanks, I hope this helps you out!
