The Husbandry of Moisture Dependent Slings

[l4nsky]

DISCLAIMER: This writeup is specifically for the husbandry of moisture dependent slings and I’m going to be talking about the controversial topic of *humidity*. If you would like to argue about the merits of its application or importance in the husbandry of moisture dependent species, please look up the definition of axiom, contemplate its relationship to the terms ‘humidity’ and ‘moisture dependent’, and then, if desired, precede to beat that dead horse with a stick somewhere else, like HERE.

Prelude​

As I’ve gotten further into this hobby, my collection has been increasingly leaning towards moisture dependent species, specifically the Asian subfamily Ornithoctoninae, and even more specifically, a healthy representation of the Phormingochilus genus with various other Ornithoctoninae members represented as well. The common theme among all of these tarantulas is the fact they fall into the category of species deemed ‘moisture dependent’, or more historically ‘swamp dwellers’ (TKG anyone?). The tarantulas in this category have historically been viewed as difficult to establish, difficult to breed, and even difficult to keep alive. Specific instructions on their husbandry in captivity is either frustratingly vague and reliant on subjective interpretation (ex: keep the substrate “moist”, a relative term that can mean one thing to one person and quite another thing to a second person) or completely non-existent at all. I shudder to think how many of these species have passed away in captivity due to improper care. Again, this usually isn’t through a deliberate will to harm the animal or malicious intent, more from a lack of understanding.

Last year, I started sharing some of the details around my breeding efforts with Phormingochilus ssp and have kept a few breeding logs of my efforts here on AB. As availability has increased and prices have started to fall, more and more novice (and experienced) keepers are diving into keeping these drop-dead gorgeous, moisture dependent species, often times attempting to raise them from slings. It can be intimidating to try and raise tarantula slings sometimes, especially if the species has a reputation of being sensitive and has a large price tag. My most recent breeding log seems to have been found by quite a few people now in their search for information on some of these species (as my inbox can attest lol). Successfully raising moisture dependent species from slings tends to offer some particular challenges that I don’t see often addressed, so I’m willing to openly share my theories and method that have brought me success. First and foremost, slings are delicate (relative term compared to the hardiness of the adults of the species), moisture dependent ones even more so. IME, slings like Phormingochilus ssp are more demanding in their requirements and less tolerant of husbandry mistakes then the hobby mainstay species. If allowed to completely dry out, molting problems or outright death are the norm. If they are kept too wet without enough ventilation, lethargy and eventual death due to stagnation are the norm. IMHO and IME, to successfully keep and raise moisture dependent slings, a balance between relative humidity and air turnover must be maintained.

Now, here’s the good news. In practice and IME, as challenging as it sounds, obtaining this balance is actually quite easy. The point of this write up is to demonstrate how I achieve this and how I’ll raise up dozens of moisture dependent slings.

Axioms and Definitions​

First things first, we’re going to start off with some axioms and some definitions for the methods I use. My goal is not only to help a hobbyist successfully raise a moisture dependent sling after reading this, but for them to understand the logic and reason that goes into this method for a more complete understanding (Give a fish vs teach to fish, Shuhari, etc).

• When compared to their adult counterparts, slings are delicate and prone to desiccation with moisture dependent species being at the highest risk. The reason is twofold. For one, slings lack a fully formed epicuticle, and as such suffer higher water losses from evaporation off the body’s surface area. Secondly, and compounding on the first, slings have a much higher surface to mass ratio then their adult counterparts, meaning they have less water to lose before reaching the point of no return and they have a larger area comparatively over which to lose it. In short, they have less moisture reserves and they lose them faster than their adult counterparts.
• A high relative humidity level will prevent the fast rate of moisture loss that leads to desiccation, but proper air turnover must be maintained to prevent CO2 buildup and stagnation as well. Notice that these two husbandry requirements clash at face value. How can you maintain high RH if you’re constantly bringing in drier air from the outside to maintain ventilation? Read on.
• The stack or chimney effect, is a passive way to maintain air circulation by relying on the strategic use of ventilation and the differences in the temperature and/or humidity between an enclosed volume of air and the external environment. Essentially warm and/or humid air will rise and if there is top ventilation, escape the enclosure. This will create a small vacuum and nature abhors a vacuum. If there is cross-ventilation on the sides, this vacuum will pull in cooler, less humid air from the outside through the cross ventilation.
  • 
• With some thought on the placement of these cross-ventilation holes and the depth of the internal substrate, this incoming air can be humidified through evaporation in the soil
  • 
    
  • …but more on that later.
• A good substrate mixture is worth its figurative weight in gold. Straight coco coir won’t make the cut (too loose, doesn’t compact well or hold shape, gives up moisture too fast). The mixture I use across all my moisture dependent enclosures is by volume – 2 parts Zoo Med Reptisoil, 2 parts dry, loose Zoo Med Eco Earth, 1 part Dry Sphagnum/Orchid Moss, and 1 part Vermiculite. I constantly keep a tote of this substrate mixed up and when I’m using it for slings, I try to remove the larger sphagnum moss pieces from the substrate (but use them a bit later instead of as a soil additive). Feel free to experiment here but for the purpose of these sling enclosures, it must hold a decent amount of water and it must be able to compact down well and stay compacted.
• Mycology is a fascinating subject (a bit out in left field, right? Give me a few lines to explain lol). Before invert keeping became my most dominant hobby, I was an avid amateur mycologist and grew various types of gourmet mushrooms (Not really plants, but…). In that hobby, the importance of RH is non-negotiable to success, and the combined importance of maintaining a high air turnover rate, maintaining high RH levels, and proper ventilation to keep CO2 levels at a minimum were necessary conditions to meet if you ever wanted to reap the fruits of your labor (all while maintaining sterility I might add). By comparison, keeping moisture dependent species has been not only similar in theme, but actually much easier in practice (Ever try keeping a greenhouse at 95% RH and maintaining a 3-5x hourly air turnover rate for weeks? Trust me, it is extremely difficult in an amateur setting.). Luckily, when I started my moisture dependent journey, a lot of these skillsets I had developed and the theories to amateur fungi cultivation bled over and have helped shape these methods that have given me success. In addition to the previously mentioned stack effect, two other designs and concepts from my mycology experience have proven vital and I’ll go over them below:
  • Field Capacity: This is technically defined as the water content of a soil after gravitational drainage over approximately a day. Basically, how much water could the substrate hold in its unaltered, uncompacted, natural state. It’s expressed as a percentage as the amount of water present in a substrate divided by the total amount of water a substrate can hold and allows mycologist to do away with such relative terms as ‘moist’ or ‘damp’ and use a common, empirical measurement for determining and discussing moisture levels.
  • Shotgun Fruiting Chamber: Inducing a block of mycelium to produce fruiting bodies (aka mushrooms) can be really difficult. Basically, you have to convince the mycelium that it’s exhausted its food supply, has reached the edges of its environment, and is about to slowly perish away. Only then will they produce the fruiting bodies with the goal being to sporulate and disperse, setting the next generation up for success before the main colony’s resources have been depleted. In practice, this means you have to take a fully colonized mycelium block and expose it to the air. Prior to cutting slits in the culture bag, the mycelium was in a 99% RH + environment with a high CO2 level from the mycelium’s own respiration (mimicking the mycelium growing throughout say a rotting log). After cutting slits, the CO2 drains out and the mycelium is exposed to drier conditions (mimicking the outer edges of the mycelium colony starting to reach the outside edge of the tree and be exposed to the open environment.) At this time RH must be kept at 95% or higher to reduce the amount of water lost from the mycelium blocks due to evaporation (mushrooms are 90% water, any loss in water for the mycelium block is a loss in eventual yield). CO2 levels (which the fungi is now producing more of as it grows the fruiting bodies) must also be kept at a bare minimum to keep the fungi in a fruiting stage and produce the best fruiting bodies. This requires a decent amount of air turnover and ventilation. Fortunately, we do have one fact working in our favor - CO2 is denser than air. So,the point of this explanation here isn’t to teach everyone how to grow fungi, it is merely to relay the difficulty in doing so. I mean after all; how would you even achieve this in a home lab? Well, enter the concept of the Shotgun Fruiting Chamber, and it’s a devilishly simple concept at that. At its core, it’s simply a tote with a whole bunch of holes filled roughly 1/3rd of the way up with some perlite at 100% field capacity. As you can imagine, it is quite humid in the tote. This humid air rises out of the top ventilation holes, pulling in air from the side ventilation holes as it does so. Now, some of the side ventilation holes are actually below the level of the perlite. This has two advantages: One being that air will still be pulled through these subsurface holes and that air will be pulled through the field capacity perlite, which will actively humidify the air by giving up some of its moisture via evaporation. A deeper perlite layer will result in a larger moisture reserve and longer time periods of stable RH. The second advantage is that the heavier CO2 from mycelial respiration that causes stagnation is allowed to bleed away through these lower holes, never pooling to dangerous levels. Shortly, we’ll see how these advantages play out in the husbandry of moisture dependent slings.

 

[l4nsky]

The Two Building Blocks for Success​

IMHO, the success I’ve had with rearing Ornithoctoninae slings can ultimately be boiled down to two simple areas of focus: The enclosure design itself (ventilation placement and amount, enclosure size, etc) and the substrate composition.

Enclosure Design​

First, we’ll go over the enclosures themselves. The base enclosure is a 5.5oz Deli Cup. A lot of experienced hobbyists are probably thinking right now that this is an absurd amount of space for a 0.5” sling and they’re right. In the end, over half of this deli cup will be packed with substrate, so they will have much less space, but more on that later.

Starting on top there are 9 ventilation holes arranged in a 3x3 grid, melted in the center of the lid.


Next, there is a 4 wide x 5 deep grid of ventilation melted on opposites side of the deli cup. For the depth spacing, start the first hole up top about ¼” down from the top and the fifth (last) hole about ¼” above the bottom, spacing out the other three to the best of your abilities (doesn’t have to be perfect). For the width spacing, please read below.


Now, when you’re spacing out the width for the side ventilation grids, the most important consideration is the Ventilation Gaps (pictured below) or the spaces between the two ventilation grids on opposite sides of the deli. This gap should be about 1.5” or more of the circumference of the deli. This space on either side of the deli devoid of ventilation holes is important moving forward and is a vital part of the design. Make sure it’s there.

Substrate​

I expanded on the substrate mixture I use earlier in this writeup, so I’m not going to go into detail again on its composition. Once again, feel free to do some research and experiment here, but keep in mind the requirements: your mixture must hold a decent amount of water and it must be able to compact down well and stay compacted. These attributes are required because we’re going to standardize the relative term moist and give it an empirical definition using a field capacity figure. For my enclosures, I shoot for a substrate around 60% field capacity (meaning the substrate is holding 60% of the water that it can hold). Don’t panic, it’s actually pretty easy to gauge this using a dirty mycology trick. For most species of edible fungi, a 60% field capacity offers the best potential for growth. A quick dirty trick to get this right in the ballpark is to squeeze (and I mean SQUEEZE) a handful of substrate. If only one or two drops comes out of your clenched fist, this should be really close to 60%. If you’re ever in doubt, always err on the side of drier as well. It’s a lot harder to take moisture out then it is to add moisture to a substrate. Going forward, proper field capacity will be defined as squeezing the substrate hard and only having one or two drops come out of your clenched fist. To achieve this, start out with a big bowl, dry substrate, water, and a mixing implement. Add water and some substrate to the bowl and stir the substrate until all the water has been absorbed. Grab a handful and squeeze it hard. If more than 1 or two drops of water drip from your clenched fist of substrate, crumble the substrate in your hand back into the bowl, add a handful of dry substrate, thoroughly remix, and test again. If it’s still too wet, repeat until you get the desired results. If the substrate is too dry, you get no water droplets out of a clenched fist of substrate, or your hands aren’t damp after you squeeze the substrate, crumble the clenched fist of substrate in your hand back into the bowl, add a little bit of water, thoroughly remix, and test again. If it’s still too dry, repeat until you get the desired results.

Substrate at proper field capacity should maintain its structure when compressed.

*Note: Dry on image left, 60% field capacity on image right. Two samples are not the same volume or weight

Substrate at proper field capacity should be visibly darker

*Note: Dry on image left, 60% field capacity on image right. Two samples are not the same volume or weight

Circling back to the Shotgun Fruiting Chamber, the success of that design is because of strategic ventilation (as discussed above in Enclosure Design) and the very porous substrate, perlite, at 100% field capacity (holding as much water as it can) that air is allowed to pass through to become humidified. Luckily, we don’t need to maintain a 95% RH (nor should we attempt to) in our enclosures like a shotgun chamber, but the same principles can be used in our favor. Instead of a loose, airy substrate with as much water as it can hold, we’ll be replacing it with a compacted substrate holding a portion of what it's capable of holding. This will slow the air down as it works through the substrate from the subsurface ventilation and reduce the rate of evaporation for the substrate as compared to a perlite shotgun fruiting chamber, resulting in a consistently higher (not 95%+) and stable RH level over time that is ideal for helping to keep moisture dependent slings hydrated and healthy. For those who haven’t read some of the writeups I’ve done on my other methods, I use the exact same design principles in my Mainstay Enclosure designs found here.

 

[l4nsky]

Construction​

Alright, now that we’ve gone over theory and design, lets talk application. At this point, you should have your enclosures created and your substrate mixture at proper field capacity. You’ll also need to acquire some orchid moss or sphagnum moss for the next steps. Now it’s time to put it all together. With the substrate mix loose, use the 5.5oz deli cup to scoop up a full container like below:


Using your fingers, firmly compact this substrate down flat, covering the bottom three rows of ventilation in the cross-ventilation grid and leaving the top two rows open and unobstructed.


Choose one of the two ventilation gaps between the cross-ventilation grids. Using your finger, create a starter burrow at this ventilation gap, compacting the substrate as you mold the burrow. There should be no exposed ventilation holes in the starter burrow. Ideally, you'll want this starter burrow to be atleast half the depth of the substrate.



Next, we’re going to add a roof to this starter burrow using moss to both encourage the sling to use this safe and ideal microclimate as well as hold a bit more moisture during husbandry activities. Start by finding a long piece that can span the starter burrow and act as a ridgepole.


Then layer up various pieces to build the entrance to a hide.



And there you have it, a completed sling enclosure specifically geared towards moisture dependent species.

General Husbandry Tips and Other Resources​

• Now, husbandry in these enclosures is fairly straightforward and simple.
• The deep, compacted substrate acts as a moisture battery per say, slowly dissipating its water vapor to maintain a consistent RH over several days. This battery will need to be replenished, but unfortunately, I can’t tell you how often. There is no one answer because this depends on the RH in your room and how fast the enclosure loses its moisture. Typically, I’m able to get a week or so between having to add water to the substrate, but this is something you’ll need to determine for your situation.
• When I do have to add moisture, I will use a spray bottle and spray the substrate at the second ventilation gap (The one pictured above in the last picture that doesn’t have a starter burrow), watching it penetrate into the substrate until it just reaches the bottom. This is actually a design feature as it allows me to standardize where I add water and avoid both flooding the sling and having water leak from the ventilation holes.
• Speaking of which, most people tend to overwater as opposed to underwater. In an enclosure with a small amount of ventilation, this can quickly prove fatal. These enclosures are designed to ‘fail safe’ in such instances, as water will drain out of the lower ventilation holes preventing swamp like conditions, and the large amount of total ventilation will quickly reduce and normalize the moisture levels in the enclosure.
• When I add water to the substrate or when I offer food, I’ll also typically mist the surface of the substrate and the sphagnum moss to give the ambient RH a little boost and offer the sling a chance to drink. Young slings that haven’t completely established a hide can freak out and bolt, but larger established slings will often think the water droplets are food and spaz out trying to catch them as they hit the webbing in their hides.
• I’m pretty sure at this point I just need to write a book. If you’re interested in other reading material on humidity or other methods I use in this hobby, here are some links to previous works:
  • https://arachnoboards.com/threads/the-paradoxical-importance-of-humidity.346451/
  • https://arachnoboards.com/threads/l4nskys-methodology.343787/

 

[curtisgiganteus]

This is absolutely amazing! Thank you for taking the time to write this up.

 

[Dorifto]

I'd give you a kiss, brilliant

 

[CutThroat Kid]

I’m going to be talking about the controversial topic of *humidity*.

look up the definition of axiom, contemplate its relationship to the terms ‘humidity’

Is it not a contradiction to say that a concept is both controversial and axiomatic?

Good husbandry tips in your article. Thanks for taking the time!

Perhaps in the near future you would share what you do when they are in the earlier nymph stages, though. I'm currently working with a recent hatch out, learning as I go.

 

[tarantulas118]

I am bookmarking all of them this is brilliant !!!

 

[l4nsky]

Is it not a contradiction to say that a concept is both controversial and axiomatic?

The importance of humidity in general husbandry is controversial. The importance of humidity (a measurement of air moisture) with moisture dependent species is an axiom.

Good husbandry tips in your article. Thanks for taking the time!

Perhaps in the near future you would share what you do when they are in the earlier nymph stages, though. I'm currently working with a recent hatch out, learning as I go.

The most common losses with Ornithoctoninae clutches is due to a low humidity level at some point in their development and IMO, the most damage is done between egg and EWL. This will manifest as bad molts later or if it's a sharp enough drop, slings stuck in the egg and unable to reach the EWL stage. IMO, it's best to try and pull the eggsack once they've all reached EWL. Throughout development, a 90%+ RH must be maintained with a 80°F temperature, and they must not be allowed to get wet. To achieve this, I stand on the shoulders of giants:

To produce my setup:


Edit: Phrasing

 

[me and my Ts]

May be getting a O. sp Vietnam silver soon so thank you, this will be helpful

 

[CutThroat Kid]

I think the term 'humidity' alone is not an axiom, as I understand that an axiom is a phrase that expresses a general truth in meaning. So, saying "up cannot be down" or "Arachnids are invertebrates" would be expressing an axiom, because the truth of the statement is granted only on the basis of the analytical meaning of terms therein the phrase (the meaning of 'up' is quite literally the opposite of the meaning of term 'down'). So saying "humidity dependent species require elevated humidity" would be expressing an axiom, but just saying 'humidity' does not express an axiom, I think, because there is no definitive claim which could be true or false being made. It does seem to be an ambiguous term, in terms of the meaning of it though. My understanding comes from my philosophy professor, who got his doctorate at Princton. Guy's way too smart, so I trust his explanation, but I'm certain there are a million ways the term is applied across various academic disciplines.

And as for the videos you linked, this is similar to what I am doing. Daves beasties is where I got the idea. But I read about someone who's filter screen panty hoe failed in the cup and drowned all their nymphs, so I have an a more basic system in place to keep humidity up. Also, my nymphs are P. Audax (jumping spiders), not that the care is much different. But I figured it was a good place to learn, and the egg was free from my WC female. lol.

 

[l4nsky]

I think the term 'humidity' alone is not an axiom, as I understand that an axiom is a phrase that expresses a general truth in meaning. So, saying "up cannot be down" or "Arachnids are invertebrates" would be expressing an axiom, because the truth of the statement is granted only on the basis of the analytical meaning of terms therein the phrase (the meaning of 'up' is quite literally the opposite of the meaning of term 'down'). So saying "humidity dependent species require elevated humidity" would be expressing an axiom, but just saying 'humidity' does not express an axiom, I think, because there is no definitive claim which could be true or false being made. It does seem to be an ambiguous term, in terms of the meaning of it though. My understanding comes from my philosophy professor, who got his doctorate at Princton. Guy's way too smart, so I trust his explanation, but I'm certain there are a million ways the term is applied across various academic disciplines.

Fixed it to use a less ambigous phrasing, thanks.

And as for the videos you linked, this is similar to what I am doing. Daves beasties is where I got the idea. But I read about someone who's filter screen panty hoe failed in the cup and drowned all their nymphs, so I have an a more basic system in place to keep humidity up. Also, my nymphs are P. Audax (jumping spiders), not that the care is much different. But I figured it was a good place to learn, and the egg was free from my WC female. lol.

I don't use nylon or pantyhose anymore because of it's wicking properties. I use Dave's design for the incubator, but use Arachnoclown's design for the incubator cups themselves.

 

[CutThroat Kid]

The importance of humidity (a measurement of air moisture) with moisture dependent species

Yeah, this is more an axiom how I understand them. Though now, I think this is a bit redundant to say, given how obvious the meaning of saying "moisture dependent" is or should be. Don't think you should have to explain that the axiom of "moisture dependence" is 'being dependent on moisture'. So, I guess I'm saying the concept of 'axioms' seems out of place here and may be overcomplicating the point of the paper for keepers, and I think you and I know a comprehensive understanding of axioms isn't really something a quick google search will elucidate for someone here just trying to learn or perfect their sling care.

I get that the 'Axiom' section is just provisional information to the piece though, and all of it is great information! When I write thesis papers for college, I usually label such sections as "preliminary information" or just "background information". Otherwise, I think this is some high-level presentation, and care to detail. I really appreciate the sectioning out, pictures, and bullet points!

For my nymphs, I have them in a typical micro critter keeper, with a partially opening lid (breeders ship juvi Ts in them often). To keep the humidity up, while also providing a drinking source, I have a 0.5Oz ampule I keep filed with water and have a fanned-out piece of medical gauze stuffed one end into the ampule. This wicks the moisture up to where it can evaporate of be consumed. I got the idea from the queen ant incubation test tube setup if youve seen those. It is basic, so I'm hoping that it is providing adequate ambient humidity. So far, I have only lost one nymph (besides the ones that escaped in my room, lol) to a poor 1st instar molt. So looks good so far.

 

[campj]

As one of the recent inbox assailants, I'm totally grateful you took the time to write this with some objectivity in mind. Great explanation!

axiom

 

[Mike Withrow]

Really nice write up and explanation. I liked the part at the end as well where you said you may as well write a book. Lol you sorta just did.

 

[l4nsky]

Really nice write up and explanation. I liked the part at the end as well where you said you may as well write a book. Lol you sorta just did.

Nah, this is more of a pamphlet than a book IMO lol.

 

[Frogdaddy]

@l4nsky Expounding further on your technique, I supposed it could be used to dry out the substrate faster?
Like for example with African species. A little moisture in the substrate, but have it dry out faster.

 

[l4nsky]

@l4nsky Expounding further on your technique, I supposed it could be used to dry out the substrate faster?
Like for example with African species. A little moisture in the substrate, but have it dry out faster.

Yes, but it's a bit beyond the scope of this particular thread . In practice though, it's quite easy to achieve with a substrate lacking moisture retaining additives that is only slightly compacted and allowed to stay somewhat loose. A loose substrate has more air pockets and thus a higher surface area than a compact substrate. The more surface area for evaporation to take effect, the faster the substrate will lose moisture and if it lacks additives to increase it's total moisture capacity, then it will become dry again relatively quickly. I've also successfully used variations of this design to raise Avicularia (also beyond scope lol).

 

[Dorifto]

Like for example with African species. A little moisture in the substrate, but have it dry out faster.

Like @l4nsky mentioned that's something easily achivable with loose substrates, but imho it goes in the opposite direction to what they need.

Usually you can find african species under rocks, crevices or compact soils with high clay on it. So even if there is little moisture on it, it takes longer to dry out, providing a more stable conditions inside their burrows. I know that some could say that rocks don't hold moisture, but they tend to coold down trapped air from beneath raising humidity levels and vice versa.

 

[campj]

A question I'm not sure I've seen addressed very thoroughly anywhere, or I'm just too stupid to remember. Once the substrate dries out a bit, how do you go about making it uniformly damp again? I see you're adding water to one side of the container, do you simply rely on the moisture leaching through the soil? How do you do it without flooding one side of the container?

Finally found time to rework the containers on the few Asian arborials slings I've got, and am still contemplating much of what you've written. Very much appreciated.

 

[curtisgiganteus]

A question I'm not sure I've seen addressed very thoroughly anywhere, or I'm just too stupid to remember. Once the substrate dries out a bit, how do you go about making it uniformly damp again? I see you're adding water to one side of the container, do you simply rely on the moisture leaching through the soil? How do you do it without flooding one side of the container?

Finally found time to rework the containers on the few Asian arborials slings I've got, and am still contemplating much of what you've written. Very much appreciated.

If your substrate mix is right, it will equalize the water content throughout the entire volume of substrate. Basically the right substrate mix will wick water evenly throughout.

@TaylorCV27 check this thread out.

I personally use 40 Dram vials over the 4oz sauce cups but they are functionally the same.