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 . 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 . 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 . 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 . 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 .
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.
2. http://onlinelibrary.wiley.com/doi/10.1 ... 202.x/full