Ideal Carapace to Abdomen Ratio

[Nepenthe56]

So after searching through the forums for a while, I couldn't find a thread addressing this specifically, so I thought I'd start one of my own. I want to know what your ideal proportions are on your spiders. I realize that this varies from species to species, but I'd like to know any general and/or species specific rules you follow. The format I prefer is carapace diameter to abdomen diameter. For example, if your ideal is for the abdomen to be 25% larger than the carapace, it would be 1:1.25. Back when I was keeping 25+ T's, my general rules were as follows:
Terrestrial Species -
MF: 1:1.25
MM: 1:1
Arboreal Species -
MF 1:1
MM 1:0.75

And for all slings I generally aimed for an even 1:1 ration, although some species seem to have naturally differently proportions for a healthy sling, so care was adapted accordingly.

Stockier terrestrial spiders usually have a lower ratio (meaning the abdomen is larger), whereas arboreal spiders usually have a higher ratio (smaller abdomen) under the assumption that they are faster and generally more sleek than their ground dwelling brethren.

Anyways, I'd like to know what kind of proportions you aim for and why. Thanks.

 

[cold blood]

Ideal proportions? You are aware of the growth cycle of a spider...well listen to me, apparently not because you searched this question.

There is no ideal size, because they do not grow like a conventional animal. They molt, and after molting, the abdomen is ALWAYS on the smaller side, and just before molting, the abdomen should be on the plump to fat side (depending on the species, as some get much fatter than others). There is no one ideal size or proportion because its always variable in ts depending on where they are in the cycle. No matter what you did, you couldn't just keep a spider at the same plumpness/proportions (if there were ideal proportions) unless it was dead and preserved. A spider's abdomen is, and should be, in a constant state of flux.


Spiders eat until they have enough in reserve to molt, they generally stop eating when they've met those reserves, and not before that, so keeping them less than plump would do nothing but significantly retard the growth rate unnaturally.

 

[EulersK]

Pretty much what CB said. Although, with slings, I aim for 1:10 regardless of species. Whether or not the spider lets me get that far is another story, but I feed them on a schedule towards that goal

 

[Nepenthe56]

Ideal proportions? You are aware of the growth cycle of a spider...well listen to me, apparently not because you searched this question.

There is no ideal size, because they do not grow like a conventional animal. They molt, and after molting, the abdomen is ALWAYS on the smaller side, and just before molting, the abdomen should be on the plump to fat side (depending on the species, as some get much fatter than others). There is no one ideal size or proportion because its always variable in ts depending on where they are in the cycle. No matter what you did, you couldn't just keep a spider at the same plumpness/proportions (if there were ideal proportions) unless it was dead and preserved. A spider's abdomen is, and should be, in a constant state of flux.


Spiders eat until they have enough in reserve to molt, they generally stop eating when they've met those reserves, and not before that, so keeping them less than plump would do nothing but significantly retard the growth rate unnaturally.

In fact I am aware that size varies based on where the spider is in its molt cycle (I've been keeping tarantulas for almost 20 years). I've also read over and over that you should avoid overfeeding your tarantulas because, due to their nature, they will overeat in case of future famines (and in my experience this is true). I believe I already stated that there is a lot of variability from species to species. I contend that there is an ideal abdomen proportion that if your spider's abdomen is smaller than, indicates it is undernourished, and if it is larger, indicates it is obese. Now that might be a more dynamic measure, but I think it exists.
Not to mention there is the notion that overfeeding will speed up the molt cycle and ultimately shorten the spider's life.

 

[Nepenthe56]

Pretty much what CB said. Although, with slings, I aim for 1:10 regardless of species. Whether or not the spider lets me get that far is another story, but I feed them on a schedule towards that goal

Thank you. They do molt so fast it can be hard to meet any sort of size goals at times.

 

[Estein]

I just want my Ts to be plump and healthy--I don't really subscribe to the idea of overfeeding. When my T is "obese" it will molt just like it has evolved to. In practice, this means that unless it is the first couple of weeks after a molt, my Ts' abdomens will be bigger than the carapace, especially with slings. Like @EulersK , I want those slings to have big ol' butts, like at least 1:4. I like ample abdomens and I cannot lie.

 

[Bugmom]

A tarantula, or any arachnid for that matter, cannot be "obese" if we are thinking about obesity in terms of obese mammals (dogs, humans, etc.) because their anatomy doesn't allow for it. You won't ever see a tarantula with cankles or a triple chin

I have never thought to consider a ratio of carapace-to-abdomen when determining if my tarantula is the "right" size. I stop feeding when I feel like the tarantula's abdomen is big enough. No idea what ratio that would be and I'm not going to start considering it. I let terrestrial and obligate burrowers get larger abdomens than I do arboreals since arboreals do more climbing, but again, that's me eyeballing it.

As for the "shortening their life" argument for power-feeding- It's humans that measure time in days and months and years. Tarantulas don't know if they're a month old or 10 years old. They know if they are mature enough to mate, and in terms of "time," that's the closest thing I can think of that a tarantula would consider in terms of their age, but it's not as if the female tarantula is thinking, "Damn, I'm 10 years old, I'd better mate or I'm going to die old and alone."

Does anyone even know what an average growth rate is in the wild? It seems it would be impossible to know. There's too many factors at play. You can't tag a sling and follow it's progress until it dies, like it's a mammal. So the whole notion of powerfeeding = shorter life is based solely off of captive raised tarantulas, and therefore, it's an arbitrary measurement based on what some humans have decided is the optimal # of years for a tarantula to live, with no control group (control group being tarantulas in the wild).

 

[Nepenthe56]

A tarantula, or any arachnid for that matter, cannot be "obese" if we are thinking about obesity in terms of obese mammals (dogs, humans, etc.) because their anatomy doesn't allow for it. You won't ever see a tarantula with cankles or a triple chin

I have never thought to consider a ratio of carapace-to-abdomen when determining if my tarantula is the "right" size. I stop feeding when I feel like the tarantula's abdomen is big enough. No idea what ratio that would be and I'm not going to start considering it. I let terrestrial and obligate burrowers get larger abdomens than I do arboreals since arboreals do more climbing, but again, that's me eyeballing it.

As for the "shortening their life" argument for power-feeding- It's humans that measure time in days and months and years. Tarantulas don't know if they're a month old or 10 years old. They know if they are mature enough to mate, and in terms of "time," that's the closest thing I can think of that a tarantula would consider in terms of their age, but it's not as if the female tarantula is thinking, "Damn, I'm 10 years old, I'd better mate or I'm going to die old and alone."

Does anyone even know what an average growth rate is in the wild? It seems it would be impossible to know. There's too many factors at play. You can't tag a sling and follow it's progress until it dies, like it's a mammal. So the whole notion of powerfeeding = shorter life is based solely off of captive raised tarantulas, and therefore, it's an arbitrary measurement based on what some humans have decided is the optimal # of years for a tarantula to live, with no control group (control group being tarantulas in the wild).

Thanks for your reply. When I use the term obese, I'm referring to a disproportionately large abdomen, which according to Andrew Smith, can lead to complications during a molt. As he put it, "In the wild tarantula spiders are lean and mean." I realize that scarcity of prey factors into this statement, but I think there's a definitely optimal healthiest size for each spider during each phase of it's life, and I'd like to know what that is. I realize that most keepers are eyeballing the ideal size for their spiders based on a preconceived notion of tarantula aesthetics.

As you said, a tarantula has no concept of time, so my in its lifespan isn't so much based on the tarantula's perception, but more on my own observation and interest in keeping my spiders as healthy as possible. I am operating under the assumption that an optimally healthy spider will live longer than a less than optimal one.

 

[cold blood]

I've also read over and over that you should avoid overfeeding your tarantulas because, due to their nature, they will overeat in case of future famines (and in my experience this is true).
I contend that there is an ideal abdomen proportion that if your spider's abdomen is smaller than, indicates it is undernourished, and if it is larger, indicates it is obese. Now that might be a more dynamic measure, but I think it exists.
Not to mention there is the notion that overfeeding will speed up the molt cycle and ultimately shorten the spider's life.

Now here it seems like your "ideal, is an "ideal" maximum size. I agree, there comes a point when an abdomen can get enormous, and some ts will continue to eat, but most will not. I do look at size once it gets too large and at that point, I will just stop feeding and await a molt.

"I contend that there is an ideal abdomen proportion that if your spider's abdomen is smaller than, indicates it is undernourished, and if it is larger, indicates it is obese."

This just isn't true, however. A smaller abdomen simply means it molted recently, a fat abdomen just means its at the back end of the molt cycle. Having that small abdomen is a natural part of a healthy spider's life.


"Not to mention there is the notion that overfeeding will speed up the molt cycle and ultimately shorten the spider's life."

This sounds logical and was something I believed strongly...until I did direct comparisons and the results were quite un-dramatic. Both groups were kept at the same 75-80 degrees and involved groups of 12-28 of A. ezendami, N. chromatus and G. pulchripes. Molt cycles were basically the same, the only real difference I noticed is that the ones fed heavily went through a longer pre-molt fast, while almost all of the ones fed weekly ate right up to the week of molting. I believe temps play the biggest role, and slower feeding schedules are often enough to still get really close to maximizing those temp effects.

I now feed every 6-10 days generally. I also feed less and less frequently as the spider gets later in its molt cycle. By the end, they're eating every 2-4 weeks.

The effect of shortening lives is really something that has a bigger effect on male's lifespans, as they will mature faster.. Its effects on females is negligible IMO.

Thanks for your reply. When I use the term obese, I'm referring to a disproportionately large abdomen, which according to Andrew Smith, can lead to complications during a molt. As he put it, "In the wild tarantula spiders are lean and mean." I realize that scarcity of prey factors into this statement, but I think there's a definitely optimal healthiest size for each spider during each phase of it's life, and I'd like to know what that is. I realize that most keepers are eyeballing the ideal size for their spiders based on a preconceived notion of tarantula aesthetics.

I've never really heard of or experienced bad molts with extremely fat individuals. IME the biggest issues with being way too large are obviously, the risk of rupture is high, one reason why enclosure height is constantly harped on here at AB. Aside from that, I've heard of issues with constantly dragging abdomens, thankfully I've never seen that in person, but plenty of videos. The other issue is that "overweight" spiders, as you would say (fine by me, I know what you mean), is that they typically don't come through molts skinny, like they should, and carry a lot more bulk. This sets the t up for a cycle of weight issues unless the t is fed sparingly throughout an entire molt cycle...this is hard for most to do, especially considering the t will be hungry.

To the best of my knowledge, there have never been any actual internal health issues with added weight, like you might find with mammals.

 

[Nepenthe56]

Thanks CB, very insightful. Seems that most people are unwittingly pushing their spiders to an aesthetic ideal (i.e. when they look big enough they cut back on feeding), though they may not realize it. Either way, I'm interested in exploring the topic further and conducting my own experiments.

 

[Steve halward]

I agree with cold blood above with the extra comment that i have an lp that sometimes go 3 or 4 weeks without my feeding because she has a huge drink..so she would not be large from over feeding but over hydrated?..ive also wondered if a well fed female would be able to produce more eggs or not..im not sure ive read anything along those lines.

 

[darkness975]

To add to this, I stopped following any kind of feeding schedule a long while ago. Now I throw food in there whenever I remember to do it (which is never consistent) and I have yet to have an issue.

My scorpions do show signs of excessive feeding more readily (they get "obese" in terms of their appearance) but it does not appear to hinder them in any real way. The fact that they cannot climb glass also helps as substrate height is less of a concern for them than it is for their cousins that can climb glass.

Side note, my B. smithi finally decided she is not an arboreal as she seems to have stopped that ridiculous climbing phase where she would sit up there for hours like an Avic.
So there's that!