Humidity, Temperature, and Tarantulas

We’ve all done it.

After hours of exhaustive research in which we read about a tarantula’s natural habitat and peruse a plethora of care sheets (many of them with conflicting information), we set up what we hope will be the “ideal” habitat for our new pet. We add the appropriate substrate, a cork hide, a water dish, maybe a plant or two, before introducing our new pet to his “perfect” home. All is well for a night or two..

And then the stress begins, as we obsess about keeping temperatures and humidity at the optimal level for this species. The care sheet said 75% humidity, but the $8 ZooMed hydrometer I picked up at Petco says it’s only 60%. Time to spray down the substrate until it’s a muddy slurry, right? Or, the temperature in my house just dipped to 68º, so I’d better put a heat lamp or mat on my critter, correct?

The short answer to both of these questions, in most instances, is a very emphatic NO.

Tarantulas are not as fragile as we make them out to be.

One very important thing to keep in mind when working with tarantulas; they are very adaptive animals. You don’t survive millions of years of evolution and climate change without being able to tolerate a dip in temperature or a bit less humidity. It’s true that some species have evolved over the centuries to adapt to different ends of the climate spectrum. Sure, a T. strimi is accustomed to living in humid conditions that would likely kill an arid species like a P. murinus. However, in between these two extremes, there is a lot of gray area and quite a large margin for error when correctly controlling the environment of your tarantula.

Now, I’m not saying that we want to keep our pets in less than comfortable conditions just to make it easier for the keepers. It’s still important to acknowledge the difference between “comfortable” and “tolerable.” It’s just very important to keep in mind that the high and low temps present in a tarantula’s natural habitat may not not represent the ideal temps for the T.

For example, consider the M. balfouri. On the island of Socotra, high temps can be in the high 90s with low temps around the low 60s. That’s a huge range, about 30º, and neither the high nor low temperatures there would make for a particularly comfortable spider. Therefore, a keeper trying to keep these exact highs and lows would be seriously missing the mark. Yet, some keepers will still obsess over keeping these highs and lows in their home setups.

Burrows = The “X” factor.

We also tend to forget that many tarantula species live in burrows and some dig them deep into the earth. This allows the spiders to escape hostile environments and to seek more humidity (or less) when needed. Temperature and humidity measurements from within tarantula burrows in the wild reveal the climates inside are much different than the outside climates. Considering that many species spend the majority of their time inside their burrows, this would mean that we actually have NO idea what the ideal humidity and temperature levels are for many of these species.

So, what do we take from this? Well, first off, it means that the temperature and humidity “requirements” included on many care sheets are next to useless and that the stress you get from not matching these numbers in your setup is also unnecessary. If you are obsessing over either, you are making the hobby more stressful than it should be.

Normal “room temperature” is okay for most species.

I hear this said on the forums all of the time, and it is a good, if slightly too vague, rule of thumb. For most folks, their normal room temperatures will be sufficient for the majority of species of tarantulas. Generally, if you’re comfortable, then your tarantula will be comfortable, too.

My all-purpose thermometer/hygrometer.

My all-purpose thermometer/hygrometer.

That being said, this rule causes confusion as normal “room temperatures” may vary from home to home. For example, in my house, we like it a bit cooler than most, so my living room at the moment is about 64º. My grandmother, on the other hand, likes it toasty, and her home is around 88º this time of year. Both of these temperatures represent extremes, and some species of Ts kept for long at either end could experience distress.

Therefore, a modicum of common sense is needed when applying this rule. If you’re cuddled up in several sweatshirts and a blanket to watch TV, then this is not a comfortable room temperature for your animals. Conversely, if it’s summer and the 89º heat in your home has your sweaty clothes sticking your body like blistered layers of skin, your Ts are not going to be happy.

The majority of the species will do well in a temperature range between high 60s and mid 80s, and will tolerate temps slightly higher and lower than these for shorter durations. If your home is 67-70º throughout the winter, you don’t have to worry about procuring some sort of alternative heat source or else risk your tarantulas dying. They may not eat as much or grow as fast (warmer temps lead to faster metabolisms) but they will be just fine.

If you should decide that you need supplementary heat…

I’ve read posts by hobbyist who live in drafty houses where the temps consistently get lower than would be appropriate. Or, there are folks like myself who have a room dedicated to raising these animals, and they purposely want to keep temperatures higher to promote growth or breeding. In these instances, it is always best to control the overall temperature of the room and not the individual enclosures.

The space heater I use in my tarantula room.

The space heater I use in my tarantula room.

The best heating option for situations like these is a space heater. There are many types available on the market, including oscillating heating fans and oil-filled electric space heaters. Most also come with built in digital thermostats and timers, allowing for you to create an optimal day/night cycle. If you do go this route, be sure to do your research and look up reviews to get the best, safest heater for your money.

And if you do decide to go with supplementary heating, please remember the following:

  • No heat mats!
  • No heat pads!
  • No heat rocks!
  • Absolutely NO Heat lamps!

Most pet store heat mats, heat pads, and heat rocks are not appropriate heating sources for tarantulas. All three can create hot spots that can injure, dehydrate, and kill a T.

That said, there are some folks that use heat mats combined with rheostats to heat their collections, but doing so takes some experimentation and finesse. If you absolutely can’t use a space heater and feel that heat mats might be a better fit, do some research and speak to keepers who have experience with these setups. Most who use them heat larger areas, like tanks or cabinets, then put the T enclosures into these. Heating individual tanks is much more tricky and risky.

Heat lamps are very dangerous and can dry out and kill a tarantula very quickly. I don’t care how many thermostats and temperature-regulating gadgets the pet industry sells, these heating sources are likely to do more harm than good.

Humidity … Stop Worrying!

NO-HYGROMETERThe anxiety created by dreaded “H” word is likely a leading cause of stress-induced hypertension in new hobbyists. All joking aside, the humidity “requirements” listed in many care sheets have created a massive issue where none should exist. Too many times, a new hobbyist will read some arbitrary humidity level on a care sheet, rush to Petco to pick up one of their cheap, inaccurate (read: USELESS) humidity gauges, then panic when they can’t hit that magic moisture number. This is a waste of time, energy, and stress that can better be spent on sports teams, money, and taxes.

It’s important to keep a few things in mind before obsessing about humidity.

  • Accurate humidity levels are almost impossible to measure with cheap, over-the-counter humidity gauges. In other words, if you’re obsessing over the number on your Zoo Med hygrometer, you are likely stressing over an inaccurate measurement.
  • Humidity requirements listed on care sheets often don’t take into account that humidity levels differ from region to region. If you live in an area with high-humidity naturally, like Florida, and you are misting down your avic, you are likely doing much more harm than good. Always take into account local climate conditions when setting up your enclosures.
  • Most species are able to thrive at many different humidity levels. Even genera like Avicularia, Poecilotheria, and Lasiodora, once thought to need much higher humidity levels, have demonstrated the ability to do very well at lower humidity levels when supplied with water dishes. In fact, some keepers now attribute many Avicularia deaths to overly-humid, stuffy enclosures.
  • Humidity levels in properly vented enclosures are often much different from those in the homes they are in. The humidity gauge in your home may read 45% humidity, but the moisture level in your enclosure may be much higher. If you go spraying the cage down, you might be raising the humidity to dangerous levels. Overly moist enclosures are a death trap.

The fact is, most species do very well in a cage that allows for proper cross ventilation (holes in the sides, not the top) and a water dish. That’s it. For Asian species, using deep, moist substrate and supplying a water dish is all that they need. They will construct burrows beneath the sub which will provide the correct humidity level for them.

Now, are there situations where you should keep an eye on moisture and humidity? Certainly. I live in New England where the winters can be cold and my home’s furnace may be running for weeks at a time. This dries the air in my home, often resulting in humidity levels in the teens. In these instances, it makes sense to run a humidifier to keep levels at a safer level (I usually opt for about 40-50%).

Slings are also more susceptible to dehydration, so many folks choose to keep all spiderlings on moist substrate with good ventilation. Slings around .75″ can also be given water bowls, which also aids in preventing them from drying out. For my tiniest slings, I keep the substrate slightly moist on the bottom, then offer sphagnum moss on the top, which I keep moist for drinking.

With proper enclosures and husbandry, humidity level should never be a factor, even if outside conditions seem less than optimal. Here are some husbandry tips that will keep you from every having to fret about humidity.

1. Keep a water dish filled with fresh water at all times.

The easiest way to keep the humidity up in an enclosure is to add a water dish. A large, open dish will allow water to slowly evaporate, raising the humidity inside the enclosure as long as it isn’t overly vented. It will also, obviously, serve as a drinking source for a parched T. For some species, like my T. stirmi, I will even include two dishes.

2. Provide Good ventilation.

A stuffy, dank enclosure can be more of a threat to a tarantula than a dry one. It’s always important to ensure that your enclosures are properly ventilated to keep the air from becoming stale and fetid. Most keepers prefer cross ventilation, or ventilation holes on the sides of the enclosure. Personally, I like to put them on all four sides to increase airflow. Cages that offer top ventilation can work, but the moisture will evaporate much more quickly. This requires that the keeper be much more diligent to keep things from drying out. .

3. Use moist soil for tropical or Asian species.

For species that appreciate a little extra moisture, I use moist, not wet, substrate. My go-to mixture for these enclosures is topsoil combined with a bit of peat moss with some vermiculite mixed in for moisture retention. It’s moist enough that it will stay together when squeezed without water wringing out of it. My O. philippinus, P. cancerides, C. discolus, P. antinous, H. gigas, and T. stirmi are all kept on topsoil mixed with some vermiculite to maintain moisture. When the levels in my room are too low, they can retreat to their dens for a more humid environment.

4. Provide enough substrate depth for burrowing.

Many keepers opt to keep Ts on shallow substrate so that they can see them out more. Although this is obviously up to the keeper’s discretion, and most species will easily adapt, it will prevent some animals from burrowing to find more suitable conditions. When in doubt, it doesn’t hurt to give the T extra depth in which to dig. Even for species that don’t dig, the extra depth will allow the bottom levels to remain moist while the top remains dry. As this trapped moisture slowly evaporates, it will elevate the humidity in the enclosure.

5. Don’t spray … make it rain.

An old juice bottle modified with some holes to be a watering bottle.

An old juice bottle modified with some holes to be a watering bottle.

Many hobbyists talk about spraying water into their enclosures to increase humidity. This technique only raises levels for a short period as the surface liquid quickly evaporates. When I want to add moisture to an enclosure, I like to “make it rain.” Using a soldering iron, I put several holes in the top of a large juice bottle and turned it into a handy watering pot. Instead of spraying water into the enclosure, I simulate a downpour and soak down one side. The moisture eventually sinks in, keeping the sub moist as the top dries up.

6. Use a humidifier.

If you live in a region with cold winters, necessitating that you use a furnace, chimney, or wood stove to heat your home, chances are that the humidity levels will get dangerously low. In these instances, even properly set up cages can dry out quickly. The best solution to this is to purchase a humidifier. You don’t need to overdo it if you go this route; a humidity level between 40 and 50% will suffice.

Don’t let needlessly worrying about temperature and humidity add stress to the hobby.

For the majority of the species available, and for all of the tarantulas I named in my Beginner Tarantula guide, room temperature and humidity will be fine. In my opinion, there is NO need to purchase a humidity gauge, as they are woefully inaccurate, and in most instances, supplementary heat is also unwarranted (and sometimes dangerous).

Is there a time where more careful, species-specific micro-climates are necessary? Yes, as those looking to breed species, especially some of the more difficult ones, will look to recreate natural environmental triggers, like high temps, winter lows, or wet seasons to stimulate a mating response. In these cases, some careful management of their tarantulas’ micro-climates will be warranted. However, for the casual keeper or for one new to the hobby, this should never be an issue.

So toss those humidity gauges and heat mats in the closet, leave the spray bottle for the plants, and stop worrying about temperature an humidity. Your Ts will appreciate it.