To listen to some keepers talk, you would think that humidity was some sort of mystical potion that was difficult to make but that works magic. While it may be tough to provide the high humidity we aim for if the air in your tortoise room is dry, the overall idea is simple. There are three basic rules to humidity-

  1. Humidity = water + energy (heat).
  2. Hot air rises, and takes humidity with it.
  3. Humidity, like heat, moves from where there is a lot of it to where there is little of it. Therefore, if the room is dry, you have to trap the humidity or it will try to humidify the entire room.

Why is humidity important?
Forest tortoises tend to come from areas of high humidity and generally do best in captivity at the right levels of humidity- at least in some places. Some species, such as Yellow-foot and some Hinge-back Tortoises, prefer very high humidity- 95% or more. Others do perfectly well at 80% or more, but can often tolerate lower levels as long as there is someplace they can hide that is more humid.

All animals loose moisture all the time- breathing, urinating, sweating (for mammals), salivating, excreting, etc. Animals need to take in water by drinking, getting it in their food, breathing it in, soaking in it, or whatever, Every species has its own plan and method. Forest tortoises live with the assumption they can get plenty of moisture by just breathing, eating juicy foods, and finding water easily, so they do not manage their water stores as effectively as grass or arid land species do.

There is often a connection made between humidity and the shell condition called pyramiding (see the Shell Problems page for more on this), but it appears that the main issue may be one of proper bone density and development- although proper levels of humidity certainly help with this and other health issues. Low humidity can also lead to dehydration and all that entails.

How much humidity?

We normally aim for roughly 70% to 100%, often settling for 70% overall with some higher ratios in certain parts of the habitat. As mentioned, some species want more humidity (some hinge-backed tortoises seem to prefer almost 100% humidity), and baby forest tortoises seem to prefer the higher levels as well.

A good layer of condensation on the glass of a warm habitat is a good sign that the humidity is about right, or you can measure it more accurately with a humidity gauge or hygrometer. 

For red-footed tortoises and most other common pet species, 50-70% overall is probably enough, especially if there are hides or other areas with higher humidity available.

Increasing humidity
We can raise the humidity in our habitat by… 

  • Increasing the amount of water available
    • Using a thicker layer of substrate to hold more liquid and thermal energy, which in turn helps equalize the air space.
    • Misting the habitat often, or using a humidifier on a timer/sensor
    • Having live plants kept well-watered and misted
    • Pouring water into the substrate
    • Using a sponge or absorbent material in a hide area
    • Offering an open pan of water
    • Adding a wall of live plants or spongy materials, as often used in terrariums
  • Increasing the temperatures, which is generally not a good idea of the temps are already where you want them.
  • Doing a better job of combining water and energy
    • Position the water dish on a heating element or under a heat lamp
    • Use substrate or undertank heating to heat the water in the substrate
    • Position a well-misted plant in a warm space
    • Aim an automatic mister/humidifier into the hottest part of the habitat
  • Doing better at trapping the humidity in the habitat
    • Covering the habitat- almost completely for most forms of humidity, only about 50-75% for heated substrates
    • Trapping the humidity in small places such as in a hide, or under a plant canopy.

The method that works best for me in the rather cold and dry Great Plains region is the one described in ‘Basic Housing’- a waterproof heat rope in the substrate that heats the water to generate warmth and humidity. My habitat is about 60% covered, and still stays very humid with very little attention- daily watering and checking water levels, and a thermostatic controller for the heat ropes so they are at the temp I want them at.

Humidity concerns
Too much humidity, especially combined with heat, low air flow, and so forth, can lead to issues like mold and mildew, a smelly habitat, plastron rot, etc. A good airflow will help, as will things like live plants, a good substrate (like cypress), and regular monitoring.

If you can, consider an airflow that lets a relatively small amount of air out at the top- small holes drilled around the edges of the lid, but has more and/or larger air holes around the base. The warm humid air will leave slowly through the high holes, and new, fresh air will come in easily in the low holes. 

What is humidity?
Absolute humidity (AH) is how much water vapor there is in a given amount of air.  (AH) is determined by dividing the mass of the water vapor (Mw) in a given volume (V), or AH = Mw/V. This is not as helpful to us as ‘relative humidity’ is. 

Relative humidity (RH) is determined by a rather complicated formula, but the idea is simply how much vapor is really in a space compared to what it could hold total. This changes as the air gets warmer, pressures change, etc.

A cubic meter of air at 30c/86f can generally hold 30 grams of water vapor (shortened to 30gr/C^3), making it 100% relative humidity. If the absolute humidity was half that- 15gr/C^3 and the temperature was the same, the relative humidity would be 50%.

As the temperature of our cubic meter of air cooled, it could not hold as much water vapor. The excess vapor becomes condensation, dew, or fog- but the relative humidity could still be nearly 100% because it is still holding as much vapor as it could at that temp. This relates to the ‘dew point’- as the temperatures drop, the relative humidity is rising. When it hits 100% and the temperatures keep dropping, the vapor it can no longer hold becomes dew.

Homemade humidity devices

These are mostly just brainstorms and ideas, not finished thoughts.

Humid Hide

Small plastic, lidded box or tub with an access hole in the side. (My example uses part of the door to make a ramp, has non-skid tape on the ramp, and curtains of plastic strips.)

Add an inch or two of dampened sphagnum moss or similar product, and park the box in a warm zone to make a nice, humid chamber. A better alternative is to sew some absorbent material (like the same kind of moss) in a thin cloth bag and hang it on a side- less moisture on the hide floor.

A small heating element (water-proof hot rock?) can be used in or under it to keep the temps comfy.

The Rainforest-enizer

This is a plan for providing warm, humidified air for a large semi-enclosed space, like a big tortoise table. It is only an idea, and this is not meant to be a blueprint!

The idea is that a ceramic element space heater (with thermostatic controls, an intake filter, and a fan speed control set to low) blows into metal ducting that leads into a large plastic tub.

Inside the tub is a powered humidifier (the thing shown is a fogger unit on a brick in a pool of water.) The inside is also divided by baffles to slow the warm air so it absorbs more humidity. A second duct takes the filtered, warm, humid air into the habitat.

Bottled humidity

Take a plastic bottle with a big mouth lid, install two tubes- a small one hooked up to an air pump on one end and an airstone on the other, and a larger tube to carry the humidified air to the habitat.

This is not a very powerful humidifier, but it is improved by adding a bigger pump, or a wick/sponge inside to help move water to vapor faster, or heating the water. It also helps to direct the output into a small, semi-enclosed space- such as inside a hiding log.

(Do you like how it is working even though the air pump is not plugged in? Gotta love that Acme brand!)


Start with an automatic pet waterer. Use 4 sponges to build a little ‘castle’ in the bowl area with a space in the middle.

Take a plastic tub that fits over the sponges nicely and cut a hole in each side and the top. Attach a small sealed fan on the top- blowing down. (Radio Shack sells small computer fans that will work. Get help if needed to wire it safely!)

Fill the waterer and set the tub down over the sponges. Trim sponges to allow a good fit.

The air will be pushed past the wet sponges and blow humidified air out the holes in the sides of the tub.

The large reservoir lets this run for a long time between services, and a drop or two of vinegar in the water will help prevent mildew.

Water wall

Mount a piece of something like terrarium moss, indoor-outdoor carpet, or similar material to a wall of the habitat. At the base of the material, park a pan or tray to catch excess water. A ‘drip vine’ along the top of some ‘reptile moss’, for example, would work nicely.

Position a dripper so it drips on the carpet. Drippers can be bought or made. Any jar with a spigot on the side will work if you can open the spigot just enough to let it drip out. A plastic milk jug with a pin hole in the side will work as well. With any dripper- how tight the lid is helps control flow.

Other ideas

People are always creating new techniques to heat or humidify reptile habitats. The internet and reptile chat rooms are a good place to get started. Some other ideas I have seen on-line include:

  • Use the ‘Bottled Humidity’ device without the lid or output tube. Just secure a jar, tub, etc. in the habitat. Fill it with water, and put a working airstone in the water, and let the bubbles do their magic. Heat the water (safe aquarium heater) as well for added benefit.
  • Actually, you could even use a small tropical fish tank with a bubbler to decorate, warm, humidify, and even light a tortoise habitat!
  • Use a clean garden sprayer with a hose and a locking trigger. Fill with very warm water, position the nozzle so it sprays in the habitat, pump it up a bunch, and just let it run. It will run through most of the tank making it a good way to get a sort of ‘deep watering’ in a semi-enclosed habitat.
  • Do not overlook the value of live plants. Almost any humidification plan can be improved by adding plants. Grow plants in the drip pan in the ‘Water Wall’ idea. Point the ‘Bottled Humidity’ tube into a cluster of live plants, etc.
  • Build a small humidifier, like this one.


Edited 8-15-2012 (C) Mark Adkins