The Humidity Mystery

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Humidity should come from substrate, not misting —

How often have we read of a keeper complaining that they cant get their enclosures to the humidity levels stated on care sheets? Or conversely, a keeper explaining, “I dont know what’s wrong – I have the humidity at the perfect level!”

For keepers with little exposure to reptiles and amphibians in the wild, or to the natural history of their animals, humidity seems to be a setting the keeper tries to achieve in order to be “perfect”. Like setting the thermostat in our houses at 70F – perfect!

We see keepers – some experienced, mostly new – stick a little hygrometer up on the wall of their enclosure where no animal lives and then try to force the humidity up to the care sheet’s recommended levels thru overhead application of water with misting systems or closing off ventilation, or both. Often with disastrous results for the animal.

I recently read a discussion where the “group expert” was explaining to a new ball python keeper that they need to get the cage humidity up to 65%. The new keeper was misting daily and closing down vents to achieve this, while the overhead incandescent was working just as hard to dry the cage down. And of course, the little round hygrometer was stuck up on the side of the cage wall refusing to comply.

This brief exchange teaches a couple important lessons. Without a knowledge of the snake’s natural history, the keeper couldn’t assess the misinformation she was getting from the group expert. And second, its not easy to create high humidity by misting. Light mists of water land on surfaces and quickly evaporate. The result is a brief spike in humidity – not very helpful.

But lets back up. Why would the group expert recommend 65% humidity anyway? Most of the ball / royal pythons we keep as captives come from the Sahel region of Africa, specifically northern Ghana and Togo. The relative humidity in these areas can average 65% for a couple months during the rains, but most of the year it is much lower, and in fact quite arid. (1) And if the animal’s natural history indicates it is adapted to a wide range of humidities, from averages as low as 20% to as high as 65%, why are the experts recommending 65% all the time? What are they missing?

Obviously, the humidity needs of any species changes over time. From hour to hour, day to day and season to season. Aiming for a single “perfect” humidity doesnt make much sense. Using our Python regis as an example, a snake laying in the sun digesting a meal at the entrance to a burrow may be bathed in near infra-red radiation, high UV levels and surrounded by very dry air. It may spend minutes or hours in these conditions, and it may descend into it’s burrow to experience much higher humidity and much lower temperatures. So why are our experts recommending 65% humidity?

Because the keeper doesnt understand the specie’s native environment, and as important, the specie’s behavior within that environment – they can’t interpret the “experts” bad advice.

So now with that in mind we can revisit the question: What sense does it make to try to increase the humidity for a ball python laying out under the warm basking lamp by misting? I hope its obvious now that this strategy is not likely to succeed.

In nature animals know that humidity is found in the ground, or on the ground under cover. Even in tropical areas the animals will experience a range of humidity. One of my first a-ha! moments came while searching for dart frogs (Oophaga) on Isla Popa in Panama. The indigenous guide insisted we could find them but it was hot and sunny, even though it had rained that morning. It was not at all what I imagined dart frog habitat to be like. But of course my guide was right and we discovered a number of them – often sitting in the hot sun! I watched though as they jumped out from under the dried leaves for a moment, then quickly hop back under them, moving from cover to cover while searching for prey, mates or whatever.

Wherever I went in Panama or Costa Rica I found the same thing – the dart frogs often on dry ground, dry forest litter, or up on dry branches and plants. Nowhere did I find the misty, foggy, sopping wet environment I saw in the dart frog hobby – or the tree frog hobby for that matter. Tree frogs were up in dry trees, glass frogs were way up in dry trees, sometimes in sunny, breezy conditions.

I eventually created some vivariums that mimicked the conditions I saw the frogs in in the wild. They worked perfectly. Occasional hand misting and a slightly damp potting mix substrate with a cover of protective leaves provided the frogs with conditions similar to what they would experience in the wild. I thought they were great, but my creations were destroyed by the dart frog community! Many became so angry that they would mount attacks on my social media groups. And of course I was immediately booted from almost all the dart frog discussion groups by the experts who couldn’t bare to witness the travesties I was recommending!

But in both of the examples, the dart frogs and the pythons, we see two important aspects of cage design. One is that humidity comes mostly from below – from the substrate – not so much from the misters above. (Misters are not bad, per se, but they are often used inappropriately. There mere presence of a misting system send many keepers down the wrong path to over watering, and poor humidity management.)

And two, our animals understand that the ground provides the humidity they need. We have to incorporate this understanding when designing cages.

A quick example: A study of cane toads showed that the animals had mental maps of their territory and selectively choose shelters that had the humid conditions they preferred. (2) I have watched my dart frogs, turtles, lizards and snakes do the same. Animals will burrow into substrates or take refuge under surface debris in order to find moisture. Even tree frogs will come down from elevated perches to get under forest litter rather than desiccate in dry conditions aloft.

This is why substrate choice (See: The Great Substrate Debate) and carefully managing the water content of that substrate (See: Managing Substrate Moisture) are two critical aspects of cage design.

1.) https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/met.2049

2.) https://www.jstor.org/stable/3892986

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