Peer Reviewed Research Regarding Power Feeding

[Justin H]

Hello everybody! I'm a new tarantula owner, and my interest is mainly scientific. I've been doing a lot of research, and honestly this forum seems to have the most up-to-date knowledge regarding husbandry. Regardless, I have access to a couple of studies that I'm unable to find being discussed on this board and wanted to share. I want to know what you guys think should be addressed in further studies and/or what methods should be altered in the experimental design. Also, have you found similar studies?


The most recent study I can find is "Growth rates of laboratory reared Honduran Curly Hair tarantulas (Brachypelma albopilosum) in response to power feeding." This study was conducted by Mario Padilla, Mary Ann Colley, and Richard P. Reading at the Butterfly Pavilion in Colorado. This study was published in March 2018 in Arachnology.

The study started with a sample size of 100 captive-bred B. albopilosums from the same egg sac. 50 of the Ts (group A) were fed "appropriately sized" meals once a week, while the other 50 (group B) were fed twice a week. Statistical analysis was used to determine that the tarantulas in group B grew significantly faster and larger than those in group A. Below are a couple of figures provided by the authors. Don't be confused by the groups switching color in the two figures.



There are a number of issues with this study. To control humidity, the tarantulas were misted once a week. According to some enthusiasts, this is a basic husbandry error and does more harm than good. Variables such as sexual maturity and lifespan were not considered--thus, while group B had larger specimens, it remains unclear whether they would still be significantly larger at sexual maturity. Gender was also not considered which possibly accounts for the variance of size within groups. Further design and experimentation are necessary, and this study provides us with a good excuse to do so.

"Sex-specific Plasticity of Growth and Maturation Size in a Spider: Implications for Sexual Size Dimorphism" by C. Fernandez-montraveta & J. Moya-Larano at the University of Madrid in Spain. This study was published in 2007 in the Journal of Evolutionary Biology. This study was actually cited in the conclusion of the previous study and can be accessed for free here (follow the link if you'd like to see figures).

This study had a larger sample size (~180) and a more disciplined method. It found that power feeding wild-caught L. tarantulas (aka tarantula wolf spiders, keep in mind they are not even in the Theraphosidae family) lead to a significant size difference in mature males. Male L.tarantulas appeared to allocate more of their resources to growth than females (this can also be referred to as having higher plasticity for the body growth trait). There was no significant difference in timing of maturation. This study cannot be used to infer anything about tarantulas, but it is evidence that gender dimorphism (at least variance in plasticity) is species specific, exists within arachnids, and deserves further research.

Any errors within this study are less obvious to me due to my limited knowledge of the topic and true-spiders. I'm pretty certain that I've fairly represented their findings, though. Let me know what you guys think.

 

[Nightstalker47]

Thanks for sharing, that is what I would expect to be honest.

I have always believed that more feeding would result in larger growth spurts between molts, especially with faster growing species...thus resulting in a larger specimen down the line. Some disagreed with me on this when I was new to the site, and insisted that this only increased growth rates and not the final size of each specimen. Well, that was not the case IME.

I conducted a similar experiment, with two N.colorativollosus, so its really not as well founded as the one above...since my sample size was far too small. It was still interesting to me though, and I wanted to know for myself just how much feeding could influence adult size. They were both sexed males, and both raised from identically sized slings into adulthood, environmental factors were the exact same. One of the males was basically fed all he could eat, sometimes getting two or three meals per week, and the other was fed once a week and then once every two weeks as time proceeded. The meal sizes were always identical, only one was fed more often. The male that was fed more sparingly, matured much smaller and one molt earlier than the male that was constantly pigging out.

The smaller specimen measured just over 5", and the male that matured one molt later...was a 7" monster of a MM. I was able to conclude in that case, that feeding more would not only increase growth rates, but also the adult size of a specimen.

 

[Justin H]

Thanks for sharing, that is what I would expect to be honest.

I have always believed that more feeding would result in larger growth spurts between molts, especially with faster growing species...thus resulting in a larger specimen down the line. Some disagreed with me on this when I was new to the site, and insisted that this only increased growth rates and not the final size of each specimen. Well, that was not the case IME.

I conducted a similar experiment, with two N.colorativollosus, so its really not as well founded as the one above...since my sample size was far too small. It was still interesting to me though, and I wanted to know for myself just how much feeding could influence adult size. They were both sexed males, and both raised from identically sized slings into adulthood, environmental factors were the exact same. One of the males was basically fed all he could eat, sometimes getting two or three meals per week, and the other was fed once a week and then once every two weeks as time proceeded. The meal sizes were always identical, only one was fed more often. The male that was fed more sparingly, matured much smaller and one molt earlier than the male that was constantly pigging out.

The smaller specimen measured just over 5", and the male that matured one molt later...was a 7" monster of a MM. I was able to conclude in that case, that feeding more would not only increase growth rates, but also the adult size of a specimen.

Wow! The sample size is too small to be significant, but those are some serious results. I would love to hear of more experiments ran by you guys. It's much easier for the enthusiast to conduct research than it is for a lab to secure funding.

 

[SDCustom78]

Just to be clear in this study, EVERY spider presented with food whether in group A or B ate EVERY time it was presented with food right?

 

[Justin H]

Just to be clear in this study, EVERY spider presented with food whether in group A or B ate EVERY time it was presented with food right?

This isn't covered in the study and is a perfect example of a variable that needs to be considered in future studies. By the end of the study only 10 tarantulas from group A and only 15 from group B survived. It makes me wonder if all tarantulas were being underfed or otherwise cared for in a way that lead to their deaths. The paper is overall not very detailed.

 

[Sarkhan42]

That kind of mortality rate is a HUGE red flag for me. How does that provide reliable data?

 

[Justin H]

That kind of mortality rate is a HUGE red flag for me. How does that provide reliable data?

I agree. I don't know how much I can share, but the following paragraph is a summation of their husbandry methods:

We collected a single Brachypelma albopilosum egg case in June 2011 from a gravid female in Butterfly Pavilion’s collection. We opened the egg case slightly to see the hatchlings and ensure the eggs were fertile. During this initial immobile, pre-larval stage, animals feed off of their stored yolk until first moult (Saul-Gershenz 1996). After moulting into the nymphal stage, individuals can move independently. At this stage, we removed the spiderlings from their egg cases and separated them. We housed each spiderling individually in an acrylic dram vial containing vermiculite and coconut substrate kept at 18–27°C and 50–80% relative humidity. We misted the spiderlings with water once per week to ensure a humid environment. As spiders increased in size, we transferred them to acrylic terrariums (starting at 11.4 × 11.4 × 3.8 cm and, eventually, moving into 33 × 24 × 10 cm as adults) with coconut fibre substrate and water provided ad libitum

Do you see any red flags here? I'll ask one of the researchers if they have any explanation.

 

[Sarkhan42]

I agree. I don't know how much I can share, but the following paragraph is a summation of their husbandry methods:

We collected a single Brachypelma albopilosum egg case in June 2011 from a gravid female in Butterfly Pavilion’s collection. We opened the egg case slightly to see the hatchlings and ensure the eggs were fertile. During this initial immobile, pre-larval stage, animals feed off of their stored yolk until first moult (Saul-Gershenz 1996). After moulting into the nymphal stage, individuals can move independently. At this stage, we removed the spiderlings from their egg cases and separated them. We housed each spiderling individually in an acrylic dram vial containing vermiculite and coconut substrate kept at 18–27°C and 50–80% relative humidity. We misted the spiderlings with water once per week to ensure a humid environment. As spiders increased in size, we transferred them to acrylic terrariums (starting at 11.4 × 11.4 × 3.8 cm and, eventually, moving into 33 × 24 × 10 cm as adults) with coconut fibre substrate and water provided ad libitum

Do you see any red flags here? I'll ask one of the researchers if they have any explanation.

Yes, it sounds as if they've separated them out at 1st instar, which is generally frowned upon among breeders, as outside poecilotheria the spiderlings don't even feed until 2nd instar, and are very fragile. This would potentially explain the lack of clustering you see at the higher end of the graph, spacing out very quickly after that large mortality early on, possibly due to mismolts etc.

 

[Torech Ungol]

I'm curious how the enclosures were heated. If it was anything other than heating the room in some fashion, that's potentially a big red flag. And that humidity... it really looks like a group of people who knew nothing about caring for Ts inadvertently did their level best to kill them. I'm overjoyed to see spider research, but this is subpar, to say the least.

 

[boina]

This is a study that I want to throw in the face of all the Europeans who insist on feeding sparingly, even slings. Thank you so much for posting.

Still, the main issue is that the slings were cared for improperly (definitely too moist). It seems, though, that well fed spiders are better at withstanding suboptimal conditions than starving spiders - not really a surprise.

And I want to point out that it's misleading to conclude spiders should be fed twice a week instead of once a week - it doesn't matter how often you feed, it matters how much you feed. I very much doubt that I have the same idea about what constitutes a 'proper sized' meal as the authors. A large meal once a week provides as much nutrition as two smaller meals twice a week.

While there are definitely issues with this, mainly the improper care, for me that's not enough to discount the results entirely.

Variables such as sexual maturity and lifespan were not considered--thus, while group B had larger specimens, it remains unclear whether they would still be significantly larger at sexual maturity. Gender was also not considered which possibly accounts for the variance of size within groups.

Er... since this is about biology it's sex, not gender.

 

[jrh3]

This isn't covered in the study and is a perfect example of a variable that needs to be considered in future studies. By the end of the study only 10 tarantulas from group A and only 15 from group B survived. It makes me wonder if all tarantulas were being underfed or otherwise cared for in a way that lead to their deaths. The paper is overall not very detailed.

The survival rate you post has nothing to do with being under fed, if they were being fed 1 time a week that is sufficient. That is not underfed, so to say the deaths were do to being under fed is bogus data. Unless im reading it wrong.

 

[Justin H]

The survival rate you post has nothing to do with being under fed, if they were being fed 1 time a week that is sufficient. That is not underfed, so to say the deaths were do to being under fed is bogus data. Unless im reading it wrong.

Well, my idea was that it could depend on the size/quality of the meal. But, here's another little excerpt:

We started spiderlings on a single wingless fruit fly per feeding. The average energy content of the fruit flies fed was 5.12 kcal/g (Bernard & Allen 1997) and their average adult mass ranged between 0.219 mg to 0.351 mg (Worthen 1996). After spiderlings surpassed 3.5 mm in length (from anterior-most
eye to posterior end of the carapace), we fed them a small 3.2 mm domestic cricket (Acheta domesticus) per feeding (commonly sold as one-eigth inch crickets). The average energy content of the adult crickets fed was 5.34 kcal/g (Bernard & Allen 1997) and their mass ranged from 103 mg as nymphs to 610 mg as adults (Clifford & Woodring 1990).

That should be enough food from what I've read on this board.

 

[boina]

The survival rate you post has nothing to do with being under fed, if they were being fed 1 time a week that is sufficient.

That's a nonsensical statement. It depends on how much they were fed. Yes, one time a week is sufficient, but one fruit fly a week is not (see below).

We started spiderlings on a single wingless fruit fly per feeding. The average energy content of the fruit flies fed was 5.12 kcal/g (Bernard & Allen 1997) and their average adult mass ranged between 0.219 mg to 0.351 mg (Worthen 1996). After spiderlings surpassed 3.5 mm in length (from anterior-most
eye to posterior end of the carapace), we fed them a small 3.2 mm domestic cricket (Acheta domesticus) per feeding (commonly sold as one-eigth inch crickets).

In that case even the 'well fed' spiders were fed much less than I give my slings and the not so well fed were definitely starved to near death. No wonder they died. That's just cruelty to animals.

3.5 mm carapace means those slings were more than 1/2" DLS - and they only got one to two tiny fruit flies a week... and afterwards they only got one or two crickts that were less than the lenght of their carapace...

My slings get fed once a week with an item about twice their carapace lenght - at least. That's twice as much as the 'well fed' slings and 4 times as much as the starved ones.

Edit: If I find the time I'm going to write a letter to the editor of the journal who published this. We definitely don't need research to prove that starving spiders won't grow well and will finally die. That feeding regime is just absurd - in both groups. We now know why the death rate was so incredibly high in both groups.

 

[Venom1080]

Cool study, poor researchers.

Like to see results from keepers who actually know what they're doing.


Thanks for sharing.

 

[cold blood]

its misleading to conclude spiders should be fed twice a week instead of once a week - it doesn't matter how often you feed, it matters how much you feed. I very much doubt that I have the same

+1 Im in 100% agreement.

I could perform a similar study that "proves" the opposite. Simply by providing super small prey to the ones fed more often and large prey to slings fed every 10 days as those in the latter group would clearly get more food and therefore plump quicker.

Its absolutely not a question if how often they are fed, but 100% what size prey they are fed.

I used to feed slings small crickets 2-3 times a week....now i feed 3 times a month basically, but i feed larger chunks of fattier prey....diced mealworms...
...ya know what, i maintain the exact same excellent growth.

All ts, slings included, require a certain amount of time to be physically prepared to molt....getting the max growth rate is merely a product of getting them their fill within that time period....for many slings, this can be accomplished in a single large meal just as easily as many smaller meals.

 

[boina]

Just to put this here: only 25 of the original 100 spiders survived to adulthood... 10 in 1x fed group, and 15 in the 2x fed group.

This is not a study, this is a desaster.

 

[SDCustom78]

I see it like this,
You cant force spiders to eat be it the right food/size or what have you . If the results go by averages as a whole between groups, the whole time, both groups have to have the same amount in them.
When you try to keep it fair by removing the ones who dont eat that week or dont eat twice that week, you have to remove the same amount from the other side as well, to keep the numbers even ALWAYS on both sides as to come up with a conclusion that was fair and balanced between groups from START to FINISH.
Sooner or later, youll have individuals going into pre molt at different times effecting who does and doesnt eat as well, not to mention others who just werent hungry when others were. Again, removing ALL the uncooperative as well as the SAME amount from the other side to keep it fair because your relying on group averages not individuals results.
You would have to keep removing more and more from either side as well as ones who did cooperate but had to be removed to keep numbers even on the other group.
Theres also removing from natural die off for unknown reasons, bad molts that ended in death as well. Sooner or later, youd be left with either none, or just one side with a few spiders by the time the results were worth mentioning but it would be one group with nothing to compare to. JMO.

 

[jrh3]

Sorry, didnt see what was being fed on the link.

 

[Justin H]

Not a nonsensical statement. He never stated he was feeding fruit flies when i posted, it was later revealed. It was stated he was giving appropriately sized food for group A 1 times a week and group B 2 times a week. So that means they were not being under fed, according to his starement of appropriately sized food.

The reason I put "appropriately-sized" in quotations was to emphasize that the authors' interpretation of appropriate is their own. I don't know enough nor have I been in the hobby long enough to know what's appropriate. I'm not allowed to post the paper in its entirety on a public forum, and I apologize if I have misled anybody. I seriously appreciate the input you guys have provided here; I'm learning a lot of valuable stuff.

 

[Nightstalker47]

Yeah upon further reading, these guys had no idea what they were doing lol.

Now I had a feeding experiment going with my L.difficilis slings in the past, but then stopped when the larger ones were around 4" and the smaller ones 2". I started feeding them equally, mainly feeding the small ones more because I felt bad. One interesting observation, the ones that were fed more often as slings are still significantly larger then the others, even now after engorging the less fed ones. Just some food for thought.

We'll see if they catch up as adults, but the others definitely still have a major head start.