Can you keep a species too dry?

purevl

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At first that sounds like a rather stupid question but there is some reasoning behind it.

Lots of times when there is a "Help, my T is stuck in a molt" thread someone suggests taking the cage into the bathroom while a hot shower is happening to increase the humidity & help the spider molt. This is always met by many others as saying this is useless becuase a T can't absorb moisture from the air like that due to the waxy coating on the exoskeleton (juvie & adult, of course, sling haven't developed this coating yet). The same thing happens when someone suggests putting the T in an ICU...others mention that ICU's are useless since the water has to be ingested, not absorbed.

Given that...does that statement of "Species X needs to be kept slightly moister than Species Y" make any sense? Sure, in the wild the amount of moisture will determine what food is available or what predators will be around or how much standing water will be available to drink. But in captivity food sources are provided by us completely independent of environmental factors, we remove all chance of predators, & we provide water bowls or drops on the web for drinking.

If a T can't absorb outside moisture, then beyond having slightly damper substrate to make burrowing eaiser for those species that do burrow...is there really a benefit to having a damper enclosure? You can certainly have too much moisture in enclosure (get mold, rot, muddy sub, whatever) but can an enclosure really be too dry?
 

Tim Benzedrine

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Well, I'm not an arachnologist, or a biologist or a -well, I'm not any kind of "ologist" at all - but i would imagine a certain amount of humidity is absorbed through the book lungs. Seems to me the importance of that would depend on the species, though.
 

Poec54

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is there really a benefit to having a damper enclosure? You can certainly have too much moisture in enclosure (get mold, rot, muddy sub, whatever) but can an enclosure really be too dry?

Yes it can, and with dire consequences. Most tarantula species grow in the tropics and subtropics, with high rainfall (at least part of the year) and high humidity. They've spent millions of years in those habitats. Keep some of them dry and you'll lose them, just like with plants. Those that have rain for most or all of the year don't need to conserve and keep moisture loss to a minimum. I keep all of my 100 species on moist substrate, except for Avics, baboon spiders from east and south Africa, and species from SW USA and northern Mexico.

What's the aversion to humidity and moisture? Been reading recommendations about keeping all tarantulas as dry as possible? Bad advice. Those people haven't kept many tropicals, and/or don't understand cross ventilation. It's pointless to keep rainforest terrestrials dry.
 

EulersK

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I'm going to make the same disclosure Tim made and say that I'm far from an expert in any of this. I've studied more biology than most, though most of that relates to mammals and reptiles... and we all know how well that transfers to arthropods.

But! Tim brought up a very good point - respiration. Certain animals are adapted to certain humidity ranges. Too dry and they lose too much moisture to the air, resulting in dehydration. Too damp and respiration becomes problematic, as fungi and parasites LOVE respiratory tracts (damp, dark, protected). Animals that evolved in humid climates have adapted safeguards against these invaders, usually in the form of routine flushing via secretions. However, this comes at the cost of losing a lot of moisture to the air. Mammals are the perfect example of this: there is a reason you see far more reptiles in deserts rather than mammals. Most mammals simply secrete too much moisture in their respiratory tract to effectively live in very dry climates.

What does this mean for arthropods? Not too sure, honestly. I'm sure some of the talk of respiration transfers to our many-legged distant cousins, but only to an extent. We all know that desiccation is a huge problem with all arthropods, which is why they have controls in place to retain as much moisture as possible (controllable spiracles, for example). However, spiders don't have spiracles - they have book lungs. This is a problem. Book lungs look like (shocker!) books, meaning there is a LOT of surface area exposed to open air. It's like that on purpose.

Mammals have high surface area in the lungs via alveoli, and the spider's surface area is simply exterior rather than interior. This is called convergent evolution: similar solutions to the same problem. Bats, birds, and insects evolved wings to face the issue of flight, though they are very far removed from each other. However, the physiology of a spider is very different from a mammal, of course. Whereas mammals use muscles to expand and contract the lungs and thus expose alveoli to the air, spiders do not have this luxury. As such, their version of alveoli (book lungs) need to be exposed at all times. You can see how quickly moisture could be lost in this scenario.

And now we enter the realm of speculation. All of this being said, I would gamble that book lungs look very different under a microscope from one species to the next. Desert dwellers likely have fewer 'pages' to the book lungs, and further have fewer mechanisms for air to meet the hemolymph. They would have evolved this to retain as much moisture as possible. Compare this to the book lungs of high humidity species, which likely have far more 'pages' and more mechanisms to aerate their hemolymph. To further speculate, note how many high humidity species are arboreal. You don't have very many low humidity species climbing trees. The argument could be made that there are simply more trees in high humidity areas, and I'm certain that's part of the reason, but I would also argue that (in general) arboreals have far, far more energy than terrestrials. The arboreals, which evolved with more humidity and thus more pages to the book lungs, resulted in more efficient respiration, which then resulted in the ability to be faster and more energetic. The trade off is quicker desiccation.

TL;DR
I would say high humidity species need the humidity to help prevent desiccation. I would also say that low humidity species would be able to handle high humidity, so long as fungi/parasites weren't an issue. Again, this is speculation, and my reasoning is above.
 

Chris LXXIX

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Yes it can, and with dire consequences. Most tarantula species grow in the tropics and subtropics, with high rainfall (at least part of the year) and high humidity. They've spent millions of years in those habitats. Keep some of them dry and you'll lose them, just like with plants. Those that have rain for most or all of the year don't need to conserve and keep moisture loss to a minimum. I keep all of my 100 species on moist substrate, except for Avics, baboon spiders from east and south Africa, and species from SW USA and northern Mexico.

What's the aversion to humidity and moisture? Been reading recommendations about keeping all tarantulas as dry as possible? Bad advice. Those people haven't kept many tropicals, and/or don't understand cross ventilation. It's pointless to keep rainforest terrestrials dry.
The truth. I keep my Megaphobema robustum, Ephebopus murinus, Hysterocrates gigas, Psalmopoeus cambridgei on the wet side in full ventilated enclosures. Overfill the waterdish as well and they are happy.
But, sorry, you said except for Avics? I mean, for what i know Avics needs a lot of ventilation and a lot of humidity, correct me if i'm wrong.
 

AphonopelmaTX

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Your question(s) are far from stupid. Most people give advice without knowing a thing about arthropod physiology and provide it based on anecdotle evidence or merely repeat what they heard.

Lets answer your main question first. "Is it possible to keep a tarantula species too dry?" Yes it is, but why. The integument (exoskeleton as a whole) of spiders, and all arthopods, not only serves to keep water out, but to keep it in. In many arthropod species, the exoskeleton shows varying amounts of permeability depending on their environment. As shown in captivity, a tropical species of tarantula such as Theraphosa blondi when kept too dry will sit by the water dish or find the spot in the cage with the most moisture. By contrast, a tarantula from an arid climate such as Grammostola rosea may show the same behavior but take far longer to reach a level of dehydration to trigger the behavior to keep as much moisture inside of its body and to replace lost moisture. The large difference in the amount of time two different species from two vastly different environments will dehydrate indicates that there could be different levels of permeability in the cuticles that make up the integument. Of course, cuticle permeability wouldn't be the only source of water loss in a tarantula. Respiration could also be another factor although I would believe a less significant one.

Lots of times when there is a "Help, my T is stuck in a molt" thread someone suggests taking the cage into the bathroom while a hot shower is happening to increase the humidity & help the spider molt. This is always met by many others as saying this is useless becuase a T can't absorb moisture from the air like that due to the waxy coating on the exoskeleton (juvie & adult, of course, sling haven't developed this coating yet).
As far as I know, no one has provided an explaination as to why increasing the humidity while a tarantula molts would help it go through the process easier. I suggest reading about ecdysis and then drawing your own conclusions. As an example though, the molting process (ecdysis) requires an increase in hemolymph pressure to pop the carapace off thus an appropriate level of hydration needs to be there before ecdysis starts. Other physiological functions also take place that I would think requires an adequate level of water in the hemolymph. Tarantulas in their natrual habitat have their way of making sure they are as well hydrated as possible by the use of burrows to make sure they don't lose water between molt cycles. In captivity, a lot of those species that use burrows in the wild do not do so in captivity (Grammostola and Brachypelma species being good examples). We as tarantula keepers have to make sure water is provided at all times either by a cup of water or providing some water in the substrate, otherwise we create an environment that can be worse than any desert on the planet. It is my opinion then that once a spider starts molting, that's it. All you can do is leave it alone and hope for the best. One can't hydrate a spider after the fact, because even without that waxy layer (the epicuticle), spiders are not one of those organisms that can absorb water from the air.

The same thing happens when someone suggests putting the T in an ICU...others mention that ICU's are useless since the water has to be ingested, not absorbed.
With the ICU, it works for some and others say it doesn't. The theory of the ICU is that water is actually taken in through the mouth by way of the moist paper towel or whatever material is moistened. See this web page for more details. http://people.ucalgary.ca/~schultz/icu10.html

If a T can't absorb outside moisture, then beyond having slightly damper substrate to make burrowing eaiser for those species that do burrow...is there really a benefit to having a damper enclosure? You can certainly have too much moisture in enclosure (get mold, rot, muddy sub, whatever) but can an enclosure really be too dry?
As stated at the top here, the answer is yes. The reason being the permeability of the cuticles that make up the integument seem to vary based on the microenvironment of where the spider came from. Tropical species appear to have a higher permeability, the arid species do not as a means to adapt to a more arid climate.
 
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awiec

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One must remember that book lungs are primitive compared to modern ways of breathing as they work similar to and look like gills. The first animals who adapted to land probably had something similar to book lungs. Now with a big passive system exposed out in the open, a tropical species could certainly dehydrate in a dry environment as water goes where ever there is less of it, from the spider to the environment. In a tropical area this isn't such an issue as the levels between the tropical spider and the air is not as stark and the spider isn't going to turn into a raisin. The reason why ICU's are advised against is that the best way to rehydrate your spider is just a drink, it's safe and the spider gets water rapidly. With an ICU you can cause more harm than good as humidity sensitive genus like avics will get "sick" and die instead of recovering. Proper airflow generally solves many issues as moving air allows not only the book lungs to function well but discourages mold growth which would love book lungs.
 

lalberts9310

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The truth. I keep my Megaphobema robustum, Ephebopus murinus, Hysterocrates gigas, Psalmopoeus cambridgei on the wet side in full ventilated enclosures. Overfill the waterdish as well and they are happy.
But, sorry, you said except for Avics? I mean, for what i know Avics needs a lot of ventilation and a lot of humidity, correct me if i'm wrong.
In the Avic situation I would say that the area you live in might also play a role in humidity.. avics are kept dry (most hobbyists have more success keeping them dry than moist), maybe not bone dry like you would a G. Rosea, but also not as moist as you would asian species or ephebopus etc, and yes they need good CROSS-ventilation.. most hobbyists keeps the substrate dry, with an occasional dribbling of water onto the sub, and a water bowl.. I have heard of people keeping avics successfully in moist conditions, however that is the minority of hobbyists, as majority keeps them drier.. IMO they should be kept dry.
 

BobGrill

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The truth. I keep my Megaphobema robustum, Ephebopus murinus, Hysterocrates gigas, Psalmopoeus cambridgei on the wet side in full ventilated enclosures. Overfill the waterdish as well and they are happy.
But, sorry, you said except for Avics? I mean, for what i know Avics needs a lot of ventilation and a lot of humidity, correct me if i'm wrong.
You're mistaken. Avics need lots of cross ventilation but substrate should be on the dry side. Lots of moisture actually kills Avics pretty easily.
 

Chris LXXIX

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You're mistaken. Avics need lots of cross ventilation but substrate should be on the dry side. Lots of moisture actually kills Avics pretty easily.
Well, that's incredible... never imagined that. Thanks for your reply. I have to say that, as a "disclaimer", i'm not into arboreals, except for two Psalmopoeus cambridgei i received as freebie, just that i've always heard and read that Avics in general need from 70 to 80% of humidity, with a full ventilated enclosure, this in order to avoid air become too stagnant that can kill them.
 

awiec

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Well, that's incredible... never imagined that. Thanks for your reply. I have to say that, as a "disclaimer", i'm not into arboreals, except for two Psalmopoeus cambridgei i received as freebie, just that i've always heard and read that Avics in general need from 70 to 80% of humidity, with a full ventilated enclosure, this in order to avoid air become too stagnant that can kill them.
I never pay attention to humidity levels, I read where the species is from to get an idea of their environment and just tweak as I go. If an avic is acting sluggish when it's no where near a molt then allowing it to dry a bit and more air flow usually perks it back up. I generally will also do a quick mist on the sides, not for humidity, but for drinking purposes, humidity is provided by other means. Avics are really the only really picky arboreal, most of them are more forgiving.
 

Spiderella

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Yes,you can

You can keep a species to dry, even A Grammostola Rosea,.And the warm shower method is correct.As the tarantulas exoskeleton is coming off,it can absorve
the warm air coming from the bathroom,if you keep the door shut .The water will avaporate and help the tarantula molt.Anyway,You can,By keeping the air to
warm,or not providing enough water.You should also have the correct kind and amount of mouisture - absorvent substrate.:coffee:
 

lalberts9310

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Well, that's incredible... never imagined that. Thanks for your reply. I have to say that, as a "disclaimer", i'm not into arboreals, except for two Psalmopoeus cambridgei i received as freebie, just that i've always heard and read that Avics in general need from 70 to 80% of humidity, with a full ventilated enclosure, this in order to avoid air become too stagnant that can kill them.
"70 to 80% of humidity" - that's just it, they don't need a specific humidity requirement, some genera like it moist and some don't, most humidity is actually provided by the water bowl itself.. most online "care-sheets" just gives bad advice.. they just need dry sub, a water bowl and cross-venting.. :)
 
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Tim Benzedrine

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Ha! I was gonna add that to my post originally and thought "No, wait to see how long before somebody else does!" :D
 

purevl

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Thanks for all the replies, gives me some stuphs to think about.

Let me add one clarification that I should have put in the original post...all my Ts have water bowls as soon as their enclosures are large enough for one so I'm not talking about a totally dry cage with no access to water. I'm really meaning 'too dry' as not worrying about damp sub or overrunning the water bowl or that type of thing. Since everyone always has access to fresh water there is no worry of dehydration even from the little bit of water lost thru respiration.

I guess a better question would have been, "Given that fresh water is always available, does Species X really need to be kept on damp sub?"
 

Poec54

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Most tropical terrestrials do better, or need, moist substrate in addition to a water bowl. Is water really expensive where you live? Where are you getting the "Keep 'em dry" advice?
 

Anubis77

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I'd be interested to know about any tarantula species that lives in a bone dry microclimate. The average humidity of their general habitat's less important than where and how they live in it. You'd think South Western Aphonopelma species hang out in the open, basking in the desert sun if you believe caresheets, but the reality is they're found in cool, humid burrows or under rocks. You can see condensation in A. chalcodes burrows at the height of summer in Phoenix. They can handle arid conditions well, but they're not going to thrive.

Bone dry with a water dish can work for Aphonopelma spp., but they don't burrow and aren't particularly active. Substrate moisture frequently leads to burrowing and less of a pet rock.
 
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