Humidity refers to the moisture content (water vapor) in the air. Humidity is a vital feature/requirement of land crab tanks (paludarium) and we need to know how to control it.
Ventilation, substrate, water bowls, temperature, etc., all affect the humidity in our land crab tanks. Controlling humidity is an essential part of this hobby.
Terrestrial crabs use modified gills for breathing oxygen, and the gills must always be kept moist hence the need for a humid environment.
Without ideal humidity, your pet crabs will not achieve maximum growth potential. I need to remind you that land, and hermit crabs can live up to 10 years or more in the right environment and conditions.
So, let’s take a look at how we can control (increase or lower) humidity in our crabitats.
1. Recommended Humidity for Land and Hermit Crabs
Depending on the species, the acceptable humidity range for a land/hermit crab tank is somewhere between 70 to 90 percent.
In this ideal humid environment, the crabs can digest and metabolize their food and nutrients better and facilitate the shedding of shells.
Land and hermit crabs are used to high-humidity environments and should not be kept in a dry tank. They need moist, and humid air to breathe properly.
If their gills dry out, they will die a very slow death caused by suffocation. The problem here is that it can take months for the crabs to succumb to it.
Inappropriate humidity is one of the reasons why people fail to keep crabs for a long time.
Without exaggeration, this means that humidity levels are literally a life or death situation for the land and hermit crabs.
| Most popular pet crabs | Recommended minimum humidity |
| Red Apple Crab | 70% |
| Black land crab | 70 |
| Marble crab | 70% |
| Thai Devil Crab | 60% |
| Red Devil crab | 75% |
| Vampire crab | 75% |
| Hermit crab | 75% |
| Tangerine-head crab | 75% |
| Halloween Moon Crabs | 80% |
| Rainbow Crab | 75% |
2. Checking Humidity Level
To achieve the required humidity level, buying a humidity meter popularly known as a hygrometer is advised. It is readily available and can be purchased in any pet store.
A hygrometer should be installed to track the humidity in the tank. It should be at least 70. A digital or analog hygrometer can be placed in the land crab enclosure.
Ideally, check the hygrometer up to two or more times during each day.
This activity is critical because when the humidity level falls below 70%, the crabs in the enclosure will slowly begin to suffocate. And this is because their modified gills tend to dry out slowly in such conditions.
With a quality hygrometer, setting the alarm if the humidity drops too low is possible.
Ensure that your hygrometer is calibrated correctly, as non-calibration can cause an error in the reading.
Example of Humidity (link to Amazon):
3. How to Increase Humidity in The Crab Tank
3.1 Trap moisture inside
The crab tank (crabitat) can be closed to trap moisture inside. The ideal type of aquarium used should be a glass aquarium measuring about 10 US gal (38 L) in volume (minimum).
The aquarium size is suitable because of spacing needs and the ability to hold adequate moisture.
We can use glass/plastic lids, blankets, or plastic wraps are required to trap moisture and insulate the crab tank.
3.2 Water bowls
Using water bowls in the tank is a good way to increase the humidity level. When the water in the bowls evaporates, it will help increase and maintain the tank’s humidity levels.
The bowl should be deep enough to completely submerge your crabs.
Terrestrial crabs cannot breathe underwater. Therefore, it is absolutely crucial to provide them with some kind of ladder (stones, fake plants, etc.) to get out of the bowls. Otherwise, they can drown.
Depending on the species, you may need either:
- a freshwater bowl or
- freshwater bowl and/or a saltwater bowl (containing water mixed with the right amount of sea salt mix).
As for the freshwater, ideally, you need to give them something like bottled spring, distilled, or RO water. Tap water will be the last choice.
Tip #1: If you have to use tap water, let it age for a day. The reason behind it is that chlorine evaporates out of water within 24 hours.
Tip #2: adding an airstone in the water bowl will also increase the humidity.
3.3 Humid Substrate
A substrate that can increase humidity can equally be used.
A great option is coconut fibers. Bricks of coconut fiber may be purchased at pet stores and soaked in dechlorinated water until they become saturated. The proof of saturation is when they begin to crumble.
Tip: test the consistency of your substrate with a pen. Stick it all the way down and pull back up. If the tunnel does not collapse, your substrate is fine.
Afterward, spread the bedding uniformly over the tank floor. The thick layer allows the crabs to bury themselves underneath the substrate.
Coconut fibers hold moisture properly hence an excellent method for increasing the tank’s humidity. They also do not allow the growth of molds on the tank’s walls, and the crab can safely consume them.
3.4 Misting
The hobbyist can spray the crabitat with dechlorinated water to increase the humidity therein.
This spraying can be done about twice daily or whenever the humidity level drops less than 70%. It’s essential to use a spray bottle to mist the enclosure.
Note: The type of water to be used should only be dechlorinated water because chlorine and chloramine are harmful to hermit and land crabs.
| Important: Use misting only as a last resort. Generally, it means that there are some fundamental mistakes in the crabitats. So, you have to check your tank setup. In addition, misting is often not recommended because of the flooding potential. As a result, you may get mold in the tank. |
3.4 Using soaked sponges
Similarly, soak a sponge in dechlorinated water until it is saturated and put in the crab enclosure. This item also serves to increase the humidity in the crab tank.
A natural sponge acquired from a pet store is preferable to a synthetic sponge. The choice is for safety reasons, considering that the crabs might want to nibble on it. The sponge can be changed once or twice daily, depending on the rate at which it dries out.
| Warning: Clean and change sponges as frequently as possible. Do not use sponges in the water dishes. Unfortunately, some hobbyists use them to keep the humidity up in the tank and as a ladder. The main problem is that the sponge becomes a source of all kinds of nasty bacteria, which is not good for the crabs. |
3.5 Room humidifiers
The room where the crab enclosure is kept should be humid. If the surrounding is humid, it would be way easier to maintain humidity in the crab. A room humidifier may suffice to raise the humidity level in the room.
Warning: Care should be taken when raising the humidity level in a room. The normal for homes is between 30 – 50%. Anything above 50% can prompt the growth of mold on the room walls.
4. How to Reduce Humidity in The Crab Tank
All of the below-mentioned ways can also be used to reduce humidity in the land crab tanks.
4.1 Ventilation
The lid of the crab tank can be opened slightly for some of the water to dry out. The mist around the tank also reduces this way.
Important: All crabs are very good at escaping if given the opportunity. So, do not open too much.
If you keep land or hermit crabs in plastic containers, you can easily drill a few small holes on two opposite sides of the walls to create proper ventilation. So, the humidity can be changed by adding more ventilation.
4.2 Using sand
Maintain a fine layer of sand on the floor of the crab tank. The sand helps soak up extra moisture and helps in the reduction of humidity.
4.3 Water control
A huge amount of water should not be present in the crab tank, either in a bowl for the crab to dip itself into or to soak or spray substrates.
Too much water causes rapid evaporation and will increase the humidity.
4.4 Temperature control
Lastly, the temperature of the crab tank can be slightly increased. When this is done, the humidity level should drop as well.
In Conclusion
In cases where the humidity level is much lower than the set point on the hygrometer, the crabs may start feeling uneasy. And in the long run, they may suffer gill infection or irreversible gill damage.
During prolonged periods of increased humidity, the hermit or land crabs will find it difficult to breathe through their organs due to the thickness of the air in the enclosure.
Sometimes, it’s common to notice very high or low levels of humidity through a sign: shell evacuation. Hermit or land crab leaving its shell often points to unacceptable living conditions and may not necessarily be the usual molting.