Air humidity vs. dampness of substrate

[Venom1080]

What's the difference? I've seen members post that humidity in the air isn't relevant to tarantulas? That all that matters is how damp the sub is? Unless it's just a misunderstanding and they're saying not to use hygrometers and only focus on sub dampness..

I'd like to hear from @cold blood and @boina on this.

 

[Moakmeister]

That’s what I’ve heard. Dampness of the substrate is actually what creates humidity in there, and it lasts for a long time. That’s the difference. When you mist the enclosure, it disappears really quickly and barely has any effect after a short time.

 

[Theneil]

What's the difference? I've seen members post that humidity in the air isn't relevant to tarantulas? That all that matters is how damp the sub is? Unless it's just a misunderstanding and they're saying not to use hygrometers and only focus on sub dampness..

I'd like to hear from @cold blood and @boina on this.

My guess is that it is mostly to keep people from trying to measure exact parameters.

Having moist sub is going to create high humidity near the surface and inside burrows and hides even in a well ventalated enclosure where the ambient air may only measure say 20%.

 

[KezyGLA]

The substrate is key for holding humidity. So that is where the focus should be.

Most hygrometers are usually wildly inaccurate, guess thats why most people deem them useless.

 

[chanda]

The advantage to moist/damp substrate is that it mimics conditions in the natural environment, and is therefore compatible with natural behavior, allowing the spider (or other animal) to select the appropriate level of moisture. If it wants a cooler, moister environment, its natural instinct is to dig down into the earth - which is also why heat pads under a tank are such a bad idea. If the substrate is too wet, it will climb or stay toward the top. Relying on misting to maintain adequate humidity is contrary to those instincts because the moisture is all up top - and dissipates quickly - so the spider that digs down for a cool, moist spot is out of luck.

 

[boina]

What's the difference? I've seen members post that humidity in the air isn't relevant to tarantulas? That all that matters is how damp the sub is? Unless it's just a misunderstanding and they're saying not to use hygrometers and only focus on sub dampness..

I'd like to hear from @cold blood and @boina on this.

The difference is where the humidity actually is, in the substrate and the 1/8" above it or in the air somewhere inside the enclosure. Yes, of course, moist substrate creates a humid sphere right above the substrate, too, and that humidity is actually where the spider sits. It usually will get less humid very fast the higher you get. So, trying to measure humidity where most people measure it, i.e. somwhere at the upper edge of the enclosure, you will always come up with lower numbers, even if your hygrometer is accurate. To get the "right" humidity up there you nearly always have to either create a swamp or restrict ventilation and it's not important anyway.

The one thing the spider needs to keep moist the most are the book lungs. Book lungs are actually very inefficient breathing organs, the most inefficient there are. The larger the spider gets, the bigger the challenge to get enough oxygen through those book lungs. A very large spider, like Theraphosa, nearly always operates the book lungs at maximum, opening the spiracles wide and thereby also opening them to the risk of possibly drying out. But luckily, those book lungs are directly above (hopefully) moist substrate, keeping the book lungs moist, too. And that's the point for every other spider that needs moisture: they need to keep their book lungs moist and working, otherwise they'll suffocate, and the book lungs are right above the substrate. It doesn't matter what the humidity is dorsal of the spider. The dorsal part of any spider (or at least any adult spider) has a tough exoskeleton that's water resistant. They don't dry out or take up water through their back, at least not in significant quantities.

Interestingly, practically all really arboreal species are much more resistant to dry conditions (Avic, Poecilotheria). I think they can't keep their book lungs in an constantly moist environment and therefore they need to have developed other methods for coping with dry conditions. I've always wanted to try out how resistant Asian arboreals are to dry conditions but I don't really dare - I don't want to risk my spiders.

 

[Greasylake]

Interestingly, practically all really arboreal species are much more resistant to dry conditions (Avic, Poecilotheria). I think they can't keep their book lungs in an constantly moist environment and therefore they need to have developed other methods for coping with dry conditions. I've always wanted to try out how resistant Asian arboreals are to dry conditions but I don't really dare - I don't want to risk my spiders.

I used to keep my P. Miranda on moist substrate, but since I never say him on the substrate I let it dry out for about a week and made sure the water dish was full. After a little while I didn't notice any problems, and I just started keeping him bone dry. I've seen him drinking from the water dish on occasion and I've yet to see any problems with him or signs of dehydration. Always very active, good eater etc.

 

[cold blood]

boina nailed it...only a thin layer of humidity is needed right above the sub....damp sub accomplishes this...which is why moisture dependent species merely require damp sub. This is why any t can be kept at any ambient humidity...as long as the sub is damp.

Too many over think this, when its really as simple as just adding water when the sub dries.

 

[Venom1080]

The difference is where the humidity actually is, in the substrate and the 1/8" above it or in the air somewhere inside the enclosure. Yes, of course, moist substrate creates a humid sphere right above the substrate, too, and that humidity is actually where the spider sits. It usually will get less humid very fast the higher you get. So, trying to measure humidity where most people measure it, i.e. somwhere at the upper edge of the enclosure, you will always come up with lower numbers, even if your hygrometer is accurate. To get the "right" humidity up there you nearly always have to either create a swamp or restrict ventilation and it's not important anyway.

The one thing the spider needs to keep moist the most are the book lungs. Book lungs are actually very inefficient breathing organs, the most inefficient there are. The larger the spider gets, the bigger the challenge to get enough oxygen through those book lungs. A very large spider, like Theraphosa, nearly always operates the book lungs at maximum, opening the spiracles wide and thereby also opening them to the risk of possibly drying out. But luckily, those book lungs are directly above (hopefully) moist substrate, keeping the book lungs moist, too. And that's the point for every other spider that needs moisture: they need to keep their book lungs moist and working, otherwise they'll suffocate, and the book lungs are right above the substrate. It doesn't matter what the humidity is dorsal of the spider. The dorsal part of any spider (or at least any adult spider) has a tough exoskeleton that's water resistant. They don't dry out or take up water through their back, at least not in significant quantities.

Interestingly, practically all really arboreal species are much more resistant to dry conditions (Avic, Poecilotheria). I think they can't keep their book lungs in an constantly moist environment and therefore they need to have developed other methods for coping with dry conditions. I've always wanted to try out how resistant Asian arboreals are to dry conditions but I don't really dare - I don't want to risk my spiders.

I can't tell you how informative and interesting that post was.

I've found asian arboreals quite resistant. I know some people keep them in nearly Avicularia humidity. Not like the Theraphosa.

So, basically, all humidity does is keep the book lungs moist. And different species have different levels of humidity needed for their lungs to function right.

 

[TheInv4sion]

Humidity of the air is effected by dampness of substrate. As the moisture evaporates the air becomes more humid. Also with burrowing species dampness of sub becomes even more important because it can create a humid microclimate within a more dry enclosure.

 

[ccTroi]

The difference is where the humidity actually is, in the substrate and the 1/8" above it or in the air somewhere inside the enclosure. Yes, of course, moist substrate creates a humid sphere right above the substrate, too, and that humidity is actually where the spider sits. It usually will get less humid very fast the higher you get. So, trying to measure humidity where most people measure it, i.e. somwhere at the upper edge of the enclosure, you will always come up with lower numbers, even if your hygrometer is accurate. To get the "right" humidity up there you nearly always have to either create a swamp or restrict ventilation and it's not important anyway.

The one thing the spider needs to keep moist the most are the book lungs. Book lungs are actually very inefficient breathing organs, the most inefficient there are. The larger the spider gets, the bigger the challenge to get enough oxygen through those book lungs. A very large spider, like Theraphosa, nearly always operates the book lungs at maximum, opening the spiracles wide and thereby also opening them to the risk of possibly drying out. But luckily, those book lungs are directly above (hopefully) moist substrate, keeping the book lungs moist, too. And that's the point for every other spider that needs moisture: they need to keep their book lungs moist and working, otherwise they'll suffocate, and the book lungs are right above the substrate. It doesn't matter what the humidity is dorsal of the spider. The dorsal part of any spider (or at least any adult spider) has a tough exoskeleton that's water resistant. They don't dry out or take up water through their back, at least not in significant quantities.

Interestingly, practically all really arboreal species are much more resistant to dry conditions (Avic, Poecilotheria). I think they can't keep their book lungs in an constantly moist environment and therefore they need to have developed other methods for coping with dry conditions. I've always wanted to try out how resistant Asian arboreals are to dry conditions but I don't really dare - I don't want to risk my spiders.

Will drinking help to rehydrate said Theraphosa to prevent desiccation?

 

[Rittdk01]

Don’t overthink. U can’t possibly get a hygrometer to read anything but 99% humidity even in the largest of theraphosa enclosures. To keep the substrate moist u just use your eyeballs.

 

[Venom1080]

Don’t overthink. U can’t possibly get a hygrometer to read anything but 99% humidity even in the largest of theraphosa enclosures. To keep the substrate moist u just use your eyeballs.

It's not a matter of overthinking, but rather learning everything.

 

[boina]

Will drinking help to rehydrate said Theraphosa to prevent desiccation?

Well, for a lot of species drinking obviously is enough, they rehydrate their book lungs from the inside. Theraphosa, on the other hand, seems to fight a loosing battle when trying to rehydrate only via drinking. It is likely that the large spiracle opening dries the lungs out too fast.

 

[Andrea82]

Thanks for the clear explanation @boina !
Bookmarking this to copy paste into new keepers posts!