HCA: Hermit Crab Association

Recently there has been much discussion about overly-aggressive hermit crabs and the underlying issues regarding the aggression. Fellow member Eugooglizer and I have been discussing what on earth can be causing this excessive aggression. All of the Es in question are well-cared for, and in the care of experienced crabbers. So why are they acting out in ways we cannot control?

Out of all of the care guides, the nutrition awareness, and general hearsay around the forum, one thing stood out in our mind that is rarely, if ever, mentioned: Vitamin D.

Vitamin D (or vitamin D3) is an essential vitamin that has heavy focus in the reptile-keeping hobby. Reptiles require higher calcium than most other vertebrates, and vitamin D goes hand-in-hand with calcium utilization. Without vitamin D, we vertebrates would be unable to put calcium into our bones. Vertebrate vitamin D deficiency results in softening of the bones, dental deformities, stunted growth, muscle spasms, depression, personality changes, and chronic pain [1]. It is also the cause of conditions such as rickets, osteomalacia, and osteoporosis.

Vitamin D is one of the most universal vitamins found in nature [2]. From coral to shrimp to elephants to oak trees, virtually every living organism on the planet has the capacity to produce vitamin D (via the sun’s UVB rays) and therefore has a metabolic need for it [3]. Even deep-sea fish that do not live within reach of the sun's rays have a small capacity to produce vitamin D via their skin.

Calcium is useless without vitamin D [2]. It is vitamin D that allows our bodies, invertebrate and vertebrate alike, to channel calcium into our skeletons (exoskeleton or endoskeleton), generate proper immune system function, and regulate cell calcium levels so our muscles can contract. Vitamin D is specifically important to crustaceans, and their need spikes in the middle of the intermolt period [4].

Any animal in captivity is likely to be deficient in vitamin D unless properly supplemented. Heck, if you don’t go outside enough, you are likely deficient in vitamin D yourself! If a hermit crab in captivity does not acquire the proper amount of vitamin D that it needs, it is likely to find that vitamin D in any place it knows to look.

What if overly aggressive crabs are not troublemakers, but are rather looking for a nutrient they are missing? When a crab cannibalizes another crab, we are fast to say the owner needs to make available more protein or calcium. However, hermit crabs are not comprised of just protein and calcium. What if aggressive crabs, crabs that attack other crabs and go after molters, are desperately seeking one of the most important vitamins of their molt cycle?

Ask yourself this: Where are my captive hermit crabs getting their vitamin D? Why are we supplementing calcium but not vitamin D? The former is useless without the latter. Our captive hermit crabs come from an environment that not only has a very high availability of UVB output via the sun, but also has high availability of vitamin D-rich foods (specifically, fresh fish). The vitamin D content of the diets we feed our hermit crabs is questionable at best (we all know nutrients tend to degrade as food is processed and stored), and a different diet coupled with drastically less UVB exposure (if any) is the perfect storm for vitamin D deficient hermit crabs.

We would like to propose the theory that not only are captive hermit crabs deficient in vitamin D, but certain species are more prone to obvious side-effects of that deficiency than others.

Our support for this theory is as follows:

• Calcium and vitamin D are directly proportional in terms of metabolism. Without vitamin D, there are serious, lethal consequences for hermit crabs. We in the hobby tend to supplement calcium, but forget about vitamin D.
• Molting problems increase with the time a hermit crab has spent in captivity. The longer a crab is in captivity, provided vitamin D is not supplemented (whether via UVB or diet), the more deficient the crab is likely to become. Without vitamin D, a hermit crab can neither build their new exoskeleton under their current one nor undergo the biochemical processes to harden their exoskeleton during a molt.
• I have noticed some long-term crabbers mention that their large/jumbo crabs are coming up from molts either the same size or are actually shrinking in size. When a hermit crab becomes deficient in vitamin D, the body can rob stores of it—in this case, the exoskeleton—and use the D3 elsewhere. As a hermit crab becomes deficient because their stores are being used up, they are no longer able to utilize calcium as they once did. This results in stunted growth, specifically “skinny” or smaller crabs, or simply a halt in growth. They are now vitamin D deficient; no more calcium usage can occur until the deficiency is corrected.
• Hermit crabs get more aggressive during the “breeding season.” This seems to be across the board, both males and females. And yet in most animals, only males show aggression toward each other during mating. However, female hermit crabs (and animals in general) have a MUCH higher requirement for calcium during breeding and subsequent egg-producing. Perhaps the male aggression is from male sex hormones, but maybe the female aggression stems from vitamin D deficiency and the inability of egg-laying females to utilize calcium.

Ecuadorians have recently been criminalized as an aggressive species, but we propose that this aggression is the result of a D3 (and therefore, calcium) deficiency. All of the “symptoms” match up. In captivity, Es have been noted to have molting problems, increased aggression, activity during the day (suggesting in the wild, they may be utilizing UVB), and increased breeding season-specific aggression.

Granted, there is no data on how long a hermit crab can store vitamin D before they become deficient without a constant source. However, it should be noted that stores are finite and any crab deprived of adequate access to vitamin D will eventually become deficient. Perhaps Ecuadorians are more sensitive to vitamin D deficiency. Perhaps Ecuadorians require higher levels of vitamin D for basic metabolic processes. Perhaps there is a genetic component to vitamin D storage, and Ecuadorians have more variability in individual capabilities to store this particular vitamin.

We are in NO way suggesting that anyone is taking poor care of their hermit crabs. We are simply stating that this vital nutrient has been looked over and missed, perhaps to the point of us causing problems for hermit crabs in captivity. We may feed the best diet we can, but the fact of the matter is the food is not as fresh as it is for wild hermit crabs; it is packaged, processed, shipped, and stored, all of which degrade nutrients to some extent. We argue that at the very least, dietary D3 supplementation should be seriously considered, especially for any crabber with overly aggressive hermit crabs. We also argue that UVB light should be considered more often than it is, because we simply don’t know the efficacy of either dietary or light D3 supplementation.

Perhaps this is a missing component in the “I have aggressive Ecuadorians” issue some members have been facing. If vitamin D deficiency is the culprit, it cannot be corrected overnight. This is an issue that has taken months and perhaps years to surface; it may take months more before it can be fixed. But for now, we know that vitamin D has been ignored—and because hermit crabs rely so heavily on calcium, this negligence may perhaps have lethal consequences.



References
1. https://en.wikipedia.org/wiki/Hypovitaminosis_D
2. http://onlinelibrary.wiley.com/doi/10.1 ... 202.x/full
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1253362/
4. https://www.ncbi.nlm.nih.gov/pubmed/1778400

I don't use UVB, but I do dust their food regularly with this stuff: http://www.flukerfarms.com/repta-calcium.aspx

And I've thought about Vitamin D deficiencies before, but there are too many hermit crabs that are 5 or 10 or 35 years into captivity who molt regularly and are healthy. Unless a somewhat large percentage is immune to the effects, I just can't see it having that much of an impact if they don't get UVB. It's not like these people are taking their crabs out into the sun every week, so some have gone decades with no exposure whatsoever.

We don't even know if crustaceans are able to produce vitamin D from sun exposure alone or if it comes specifically from diet. Or if they even need D to be able to properly absorb calcium. Has anyone been able to find scientific proof of that yet?

wodesorel wrote: And I've thought about Vitamin D deficiencies before, but there are too many hermit crabs that are 5 or 10 or 35 years into captivity who molt regularly and are healthy.

We were actually discussing Carol of Crabworx's hermit crabs that lived into their 30s. She fed them commercial food, and they both had access to UVB. Many commercial hermit crab foods have vitamin D added, and UVB... well, that's how they make vitamin D.

wodesorel wrote: Unless a somewhat large percentage is immune to the effects, I just can't see it having that much of an impact if they don't get UVB. It's not like these people are taking their crabs out into the sun every week, so some have gone decades with no exposure whatsoever.

Which ones, though? Carol's always had access to UVB light-- I don't know any other crabs that went decades without UVB exposure. I've been supplementing my 8 year old ruggie with some kind of reptile-grade D3 virtually since the day I got him. I also mentioned in my post, we do think that certain species are more prone to deficiency than others. It's like color; people note crabs' colors are improved by UVB, we may not know exactly how quite yet but certain species are more affected than others.

wodesorel wrote: We don't even know if crustaceans are able to produce vitamin D from sun exposure alone or if it comes specifically from diet. Or if they even need D to be able to properly absorb calcium. Has anyone been able to find scientific proof of that yet?

Yep; please read the references I posted, specifically number 2.

How did Carol's crabs have access to UVB? I thought she kept them indoors and UVB doesn't penetrate glass.

Vitamin D is in high amounts in the fish food I feed my crabs, and it's a very hearty vitamin, the fish doesn't have to be fresh. My aggressive E's were that way since i got them, so maybe they were lacking it in the wild before they were picked up but it's un-likely. I believe is a bit of a red herring though, that maybe it is something, but I don't believe it's lack of vitamin D. They would get worse diseases then a little aggression from that.

As a side note I do believe they need UVB, it's the whole reason i built a sundeck for them, but for me it was to prevent stuff like metabolic bone disease.

kuza wrote:Vitamin D is in high amounts in the fish food I feed my crabs

Precisely why I am suggesting they may need both dietary supplementation and light. Do you supplement calcium? Why not vitamin D? Calcium is in a wider array of foods, and your crabs likely get more calcium from their diet than vitamin D... however, because of the direct relationship between vitamin D and calcium, they may not be able to use it all.

kuza wrote:My aggressive E's were that way since i got them, so maybe they were lacking it in the wild before they were picked up but it's un-likely. I believe is a bit of a red herring though, that maybe it is something, but I don't believe it's lack of vitamin D. They would get worse diseases then a little aggression from that.

There is also the possibility that your Es became deficient because of the shipping process; there's really no way to know how long they were deprived of UVB light and/or necessary food before coming to you. As we mentioned in the above post, there's also now way to know how long it takes a crab to become deficient... and because of the variability of genetics in general, certain crabs may be predisposed to deficiency.

kuza wrote: As a side note I do believe they need UVB, it's the whole reason i built a sundeck for them, but for me it was to prevent stuff like metabolic bone disease.

Metabolic bone disease is essentially what we're talking about here; only in hermit crabs, not reptiles. Hermit crabs do not have bones, so they can't get metabolic bone disease. Fun fact, though... metabolic bone disease is caused by vitamin D deficiency. So you added the UVB light to prevent vitamin D deficiency? I guess we're on the same page, then..?

I am curious, though... what other reasons do you think they need UVB for? Other than vitamin D production, it doesn't benefit organisms in any other quantifiable way. Is it for a reason specific to another need?

I immediately think of my emperor scorpions - they need absolutely no UVB in order to process the calcium of their exoskeletons. Not all animals do need it, and hermit crabs are nocturnal enough to perhaps be part of that group. They instead absorb it exclusively from the animals they consume.

Also, that paper says they found vitamin D in crustaceans, but not where it came from:

"Numerous animal species far back in evolutionary history have been shown to contain 1,25(OH)2D including terrestrial crustaceans (18), sharks, lamprey, as well as frogs and fish (15), but the site of production in most of these species is not known. "

and

"but in terrestrial crustaceans, the digestive tract, and in particular the hepatopancreas, cardiac stomach and posterior caecum play the key role (44). "

Not once did it say this production came from UVB. In fact, it looks like it may be dietary.

I also have never read that Carols crabs received UVB. She kept them in an aquarium or loose in her house, but she never took them outside and I've never seen reference to her buying a reptile light for them. If anything, it was a very well rounded diet and clean conditions that led to the living so long. (She is a microbiologist, so she gave a lot of thought in how to care for them.)

kuza wrote:How did Carol's crabs have access to UVB? I thought she kept them indoors and UVB doesn't penetrate glass.

Vitamin D is in high amounts in the fish food I feed my crabs, and it's a very hearty vitamin, the fish doesn't have to be fresh. My aggressive E's were that way since i got them, so maybe they were lacking it in the wild before they were picked up but it's un-likely. I believe is a bit of a red herring though, that maybe it is something, but I don't believe it's lack of vitamin D. They would get worse diseases then a little aggression from that.

Considering that Es are known to be much more active during the day compared to many other species, it's possible that their bodies have adapted to use d3 they synthesize in response to UVB exposure in higher amounts than dietary d3. Bodies definitely recognize them and process them as being different, otherwise no animals would require UVB exposure.

And I wouldn't really consider d3 a "very hearty vitamin", it's subject to oxidation--more so than other fat-soluble vitamins actually. This is actually an issue even with actual supplements containing d3, it's important to make sure you're using one that derives it's d3 content from a high-quality ingredient and in a form that can be effectively metabolized. While feeding a diet that includes foods rich in d3, when it comes to animals being kept in captivity, extra supplementation is almost always needed to prevent deficiencies even when providing very appropriate and varied diets. Even people feeding raw diets to their cats or dogs for example have to be extremely careful to ensure they're also supplementing it with the appropriate vitamins and minerals in the required amounts, and why it's so important that people keeping reptiles use the appropriate supplements even when feeding a very healthy and varied diet.

Also - there are other members on here who have had their crabs for 8 or 10 years, never using UVB or taking them outside. I can't find the posts right now, but there have been many! Nearly all crabs that are pets have been UVB deprived for the entire length of their captivity.

I also believe it's a far fetch to assume the crab can sense it's own vitamin D deficiency and become violent because of it. And for only that species to do this. I think that would need to be proven first.

wodesorel wrote:Also, that paper says they found vitamin D in crustaceans, but not where it came from:

"Numerous animal species far back in evolutionary history have been shown to contain 1,25(OH)2D including terrestrial crustaceans (18), sharks, lamprey, as well as frogs and fish (15), but the site of production in most of these species is not known. "

and

"but in terrestrial crustaceans, the digestive tract, and in particular the hepatopancreas, cardiac stomach and posterior caecum play the key role (44). "

Yes, but it also stated:

"Production of vitamin D from its precursors necessarily requires exposure to UVB radiation and so takes place in sun-exposed tissues – the skin in animals and the leaves in plants. At least in animals, other tissues acquire the ability to produce first 25(OH)D and then 1,25(OH)2D, perhaps to give the animal better regulation of 1,25(OH)2D production and/or secretion."

and

"Numerous animal species far back in evolutionary history have been shown to contain 1,25(OH)2D including terrestrial crustaceans, sharks, lamprey, as well as frogs and fish, but the site of production in most of these species is not known."

I would also like to point out

"Vitamin D-binding proteins in the blood have been found as far back in the evolution as amphibians and reptiles. Their presence in more primitive animal forms and plants has not been described, but their existence seems likely."

Just because we have not looked for it does not mean it isn't there. The paper mentions that plants, and plants alone (and only some plants at that, the rest need sun), have been found to contain an enzyme that can synthesize vitamin D, whereas every animal studied even the ones who live in areas where they will NEVER see sunlight) have the capability to produce vitamin D via their skin. Why would one species be any different?

I don't think it's an either/or thing. I think hermit crabs can benefit from both dietary and UVB vitamin D supplementation. In fact, many animals require both-- humans certainly can't get enough vitamin D from the diet, though it is possible. If I had overly aggressive crabs, I guess I would be trying absolutely everything to see what the problem is-- and vitamin D deficiency correction just seems like a no-brainer. Even with dietary D3 supplementation, it is still very easy for many species to become deficient. (I was on a multi-vitamin and eating a healthy diet and was still D3 deficient-- sometimes it just happens.)

wodesorel wrote: I also have never read that Carols crabs received UVB. She kept them in an aquarium or loose in her house, but she never took them outside and I've never seen reference to her buying a reptile light for them. If anything, it was a very well rounded diet and clean conditions that led to the living so long. (She is a microbiologist, so she gave a lot of thought in how to care for them.)

I remember reading that she not only took them outside, but had an outdoor enclosure for them. They were regularly exposed to the sun's rays for UVB, not a reptile light.

Also - there are other members on here who have had their crabs for 8 or 10 years, never using UVB or taking them outside. I can't find the posts right now, but there have been many! Nearly all crabs that are pets have been UVB deprived for the entire length of their captivity.

And here I am, saying I've had crabs for 8 years and have supplemented D3 the whole time. In the interim, I have never had any deformed molters, attacked molters, or overly aggressive crabs.

kuza wrote:I also believe it's a far fetch to assume the crab can sense it's own vitamin D deficiency and become violent because of it. And for only that species to do this. I think that would need to be proven first.

Well, I guess that's why this is just a theory and proposal. I'm still waiting to hear why you added the UVB light if not for D3 supplementation.

kuza wrote:I also believe it's a far fetch to assume the crab can sense it's own vitamin D deficiency and become violent because of it.

Also wanted to say, I got depressed when I was D3 deficient... and that's not a normal state for me. No, I didn't magically know I was deficient, but it does affect the body as a whole-- maybe not in the same way for every person, but humans at least can express the different ways D3 affects personality.

I added UVB specifically for Vitamin D synthesis. And I agree lack of sunlight makes people depressed, the winter blues if you will. So if my crabs were getting depressed or if all my E's became aggressive after not having UVB for a while, then I'd lean towards this theory. But as it stands, I just don't believe that's what causing some E's to be aggressive.

There was a paper posted before where they watched E's in their natural habitat and they mention constant fighting for shells and general aggressive behavior. Maybe wode can find it again. But I'm not just going based on my own experience, I've read this paper before as well and then all the combined experiences of people across all the forums puts the statistics on it being a species thing. I don't have time to fish all this stuff up, I have a lot of other stuff to worry about at the moment but that paper would be eye opening for you.

I would really like to see where you saw that Carol took them outside. I obsessively read everything I could about Kate and Jon when I first started crabbing, and nowhere did it ever mentioning her taking them outside of her house or apartment. They were always outside the tank but I never read anything about her taking them outside the house.


And kuza - it's not that the crabs could sense a Vit D deficiency and react to it, it would be that the deficiency would cause major changes in their bodies and brains that would then cause them to act abnormally. It's a known sign of deficiency in mammals, for instance.

Of course, you can also get the odd mammal like myself who reacts in odd and painful ways when they GET too much Vit D, even if the doctors are insisting I'm "severely deficient" when I refuse to take supplements. Or when I get too much sun.

There is a lot that's unknown about Vitamin D, and it's also very easy to get too much with supplementation which can also cause severe health problems. It's something that has to be monitored closely in humans, so the same could be said to any animal we have captivity and that we supply unnaturally. In reptiles, doing without is known to kill them quickly, so supplementing is always seen as the better choice. However, not much study has been done into what happens if they were to get too much for too long!

Also, the more research they do into Vitamin D, the more they think it's a type of hormone and the less they think it's an actual vitamin. Which is kind of cool. :)

kuza wrote:I added UVB specifically for Vitamin D synthesis. And I agree lack of sunlight makes people depressed, the winter blues if you will. So if my crabs were getting depressed or if all my E's became aggressive after not having UVB for a while, then I'd lean towards this theory. But as it stands, I just don't believe that's what causing some E's to be aggressive.

There was a paper posted before where they watched E's in their natural habitat and they mention constant fighting for shells and general aggressive behavior. Maybe wode can find it again. But I'm not just going based on my own experience, I've read this paper before as well and then all the combined experiences of people across all the forums puts the statistics on it being a species thing.

I get the feeling you may have misunderstood the point of this post. We're not saying Es are not aggressive as a species. We're saying some, maybe all, of the aggression can be explained by a deficiency of this nature. And perhaps other things like jumbos that have been stunted in growth (sound familiar?), or crabs that seem to get smaller with molts. Hermit crabs in general show some symptoms of vitamin D deficiency (see bulleted list).

I don't mind a hearty debate, but we took the time to post scientific references to back up our review of literature and our synthesis of our theory. I (along with, I'm sure, Eugooglizer), would appreciate the same.

It just described a shell fight, although they did say they saw it happen several times: http://www.biologiatropical.ucr.ac.cr/a ... -Crabs.pdf

They come from a very unforgiving place with very limited resources. In some areas they're completely nocturnal because of the heat and lack of cover during the day.