Moist substrate - necessity or myth?

[cold blood]

Although I have no scientific facts to back this, it would seem as if the waxy layer developed in juvies and adults, is much more significant with species that live in drier climates...and it really makes sense as those are the ones in the harshest environments.

Conversely, those that live amongst much moisture, like the aforementioned Lampropelma, must not have as thick or as effective of a layer as those drier desert species, making them much more prone to dehydration during dry phases.

Slings have not yet developed any waxy layer, which is why they are almost always kept on damp substrate, because they are naturally more prone to dehydration.

 

[cold blood]

The question was about why moisture dependent species don't just rehydrate using a water dish. Since they don't what you are saying can't always be true.

They do....My moisture dependent species often lay in their water bowls, especially in winter when the air is much drier.

 

[cold blood]

Still leaves me with another question, if it uses the soil to drink from, why couldnt it just use the waterbowl instead? They live in small enclosures so it's not much of a walk for them to reach the water?

You can, and many long time keepers do just this. We suggest water bowls because it is like a safety blanket always there just in case. Given the preference, ts will generally rather drink from a water source, its just easier.

but in he hobby it is difficult to maintain an 80 to 95% humidity so the spider will walk to the waterdish/wet corner if needed...

In the hobby its pointless to maintain high humidity levels. Its just a matter of keeping the sub damp....your ambient humidity in your particular area will dictate how much water you add and how often it needs to be added. Just the term humidity over-complicates things for newer keepers....It would be a lot easier for newer keepers to be successful if the hobby stopped using the term altogether. Moisture dependent is a far easier term to relate to....its also something you can measure by just looking at your sub...is it dry? If yes, add water, if no, do nothing....its really that easy....over-complication in this area would come to an abrupt end if we used better terms.

 

[smitje]

Thanks Coldblood, enlightening. I actually found some scientific research just now that relates to the subject. It shows some surprising figures but also confirms your statements. They do evaporate, surprisingly fast and at different rates (depending on temperature alone in this case) even between the same species! Let alone different species from oposite climates.

https://www.researchgate.net/profil...e-central-Andes.pdf?origin=publication_detail

 

[smitje]

Dont know where I read it again but its ringing in my head "tarantula's have a skin that does not allow for evaporation" I think that started my confusion also......

 

[boina]

They do....My moisture dependent species often lay in their water bowls, especially in winter when the air is much drier.

Ok then, why do those species need moisture in the substrate at all if they can and will just drink?
Why do Ts die from dehydration if exposed to too high temps? (heat pad, heated stone, spot light, whatever)

 

[smitje]

Ok then, why do those species need moisture in the substrate at all if they can and will just drink?
Why do Ts die from dehydration if exposed to too high temps? (heat pad, heated stone, spot light, whatever)

Check the article, they can dehydrate pretty fast, especially at higher temps. Their evaporation speed reduces with higher humidity. I guess it just cant proces enough water by drinking to keep up when conditions are off.

 

[cold blood]

Ok then, why do those species need moisture in the substrate at all if they can and will just drink?
Why do Ts die from dehydration if exposed to too high temps? (heat pad, heated stone, spot light, whatever)

Some good questions indeed. I would assume that their internal fluid loss is greater (occurs at a higher rate) at higher temps, and even greater with heat sources.

 

[boina]

Check the article, they can dehydrate pretty fast, especially at higher temps. Their evaporation speed reduces with higher humidity. I guess it just cant proces enough water by drinking to keep up when conditions are off.

I read the article and no, you can't conclude that. They unsurprisingly dehydrate faster at higher temps, but that's still pretty slow. It should be easy for them to replace the water loss by drinking.

 

[smitje]

"The total water loss during the time of the trials (2.5 h) at 40 °C was 68.97 mg (1.28% of the initial body weight (mbi)) in the Dry sample and 103.10 mg (1.78% mbi)"

1.78% of their total body weight in 2,5 hours

"which means that these spiders could loss 12.3% mbi and 17.2% mbi, respectively, probably reaching their maximal limit of desiccation tolerance"

That would mean that worstcase scenario they would be dead in 7 hours.

This is probably where their instinct starts playing a role as you said before, they are used living without and probably dont have the sense to constantly top up. It will probably drink but just not enough. I agree the article shows only a minor difference between the wet and the dry season but its about 1 species. Evaporation rates could be me much higher with different species and differences between humidity levels. Due to origin and adaptation to local circumstances.

 

[boina]

"The total water loss during the time of the trials (2.5 h) at 40 °C was 68.97 mg (1.28% of the initial body weight (mbi)) in the Dry sample and 103.10 mg (1.78% mbi)"

1.78% of their total body weight in 2,5 hours

"which means that these spiders could loss 12.3% mbi and 17.2% mbi, respectively, probably reaching their maximal limit of desiccation tolerance"

That would mean that worstcase scenario they would be dead in 7 hours.

This is probably where their instinct starts playing a role as you said before, they are used living without and probably dont have the sense to constantly top up. It will probably drink but just not enough. I agree the article shows only a minor difference between the wet and the dry season but its about 1 species. Evaporation rates could be me much higher with different species and differences between humidity levels. Due to origin and adaptation to local circumstances.

I agree. Keep those numbers for the next person who wants to use a heat pad.

 

[smitje]

I agree. Keep those numbers for the next person who wants to use a heat pad.

I do use them, its really cold in the Netherlands

 

[boina]

I do use them, its really cold in the Netherlands

You use heat pads? But why? It's just as cold here, but not inside.

 

[smitje]

Er - what? You mean you use heat pads?

There is a big gap between the actual pad and the enclosure so it doesnt produce contact heat. Temps in the gap vary between 19 and 22 celcius. Its digitaly monitored, don't worry

 

[smitje]

Here is another interesting article about what that little creeper is actually doing when sitting on her rock. It shows no relation to humidity but it does show how its loosing moisture.

https://www.researchgate.net/profil...m-Chilean-Andes.pdf?origin=publication_detail