HCA: Hermit Crab Association

Just 'remodeled' Capt. Jack's home! Sub is anywhere from 4-6 inches as I kinda made a few deeper spots.
Fed a fresh meal including sardine, crushed coral/sand dollar, and shrimp mix.
Only question is should I reposition the heater on the back of the tank?


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Great work! What a nice little home you have made.

I think the heater is in a good spot -- you want it above the substrate (so you don't dry it out) and I prefer to put mine more towards one side of the tank so there is a slight gradient and the crabs can move where they are most comfortable. If you do this, I suggest putting a thermometer on each side of the tank just to make sure you stay within the range.

In terms of improvements, I think the substrate could still be deeper. I'm not sure how big your crabs are, but I put mine at 7 in all around. It may feel wasteful to use up half your tank with substrate, but your crabs will thank you! Also, what are you doing for water? There should be a salt water pool deep enough for your biggest crab to completely submerge itself (shell and all). I think you would benefit from checking out the care sheets in the forum - I found them extremely useful when building my tank.

Now you are on to the fun part! Which is making little things for them to play with, trying new foods, and spying on their little crabby lives

nerdycrabs wrote:Great work! What a nice little home you have made.

I think the heater is in a good spot -- you want it above the substrate (so you don't dry it out) and I prefer to put mine more towards one side of the tank so there is a slight gradient and the crabs can move where they are most comfortable. If you do this, I suggest putting a thermometer on each side of the tank just to make sure you stay within the range.

In terms of improvements, I think the substrate could still be deeper. I'm not sure how big your crabs are, but I put mine at 7 in all around. It may feel wasteful to use up half your tank with substrate, but your crabs will thank you! Also, what are you doing for water? There should be a salt water pool deep enough for your biggest crab to completely submerge itself (shell and all). I think you would benefit from checking out the care sheets in the forum - I found them extremely useful when building my tank.

Now you are on to the fun part! Which is making little things for them to play with, trying new foods, and spying on their little crabby lives

I do have both a salt & fresh water pool, they are just separate from each other haha they may not be very visible in my pics.

I am getting super excited to add another crab or two & experiment to see which foods are favorites!!

I agree with deeper substrate; both fresh and MSW sources need to be deep enough for crabs to submerge (so they can regulate the contents of their shell water); and I would not add more than one additional crab (and a small one, at that). Crabs do "like" to have a buddy, but each additional crab does not just add, but multiplies, the chances of aggression and of molting cannibalism. More is not better, with captive wild animals.

DragonsFly wrote:I agree with deeper substrate; both fresh and MSW sources need to be deep enough for crabs to submerge (so they can regulate the contents of their shell water); and I would not add more than one additional crab (and a small one, at that). Crabs do "like" to have a buddy, but each additional crab does not just add, but multiplies, the chances of aggression and of molting cannibalism. More is not better, with captive wild animals.

How do they multiply? Isn't is rare to have captive breeding. Anyways I have 2 in a 10 gallon that are completely fine with each other and they do cuddle alot, so I think 2 small ones will be fine since it's a small tank and they do get lonely and travel in packs of a 100 and more in the wild

She didn't mean multiply as in breed, she meant multiply as in greatly increase the chance of aggression between crabs in the tank. The more crabs you add to a small space, the more they have to compete for resources. The competition can lead to aggression.

To Giner13--your tank looks real nice, but I agree with the others that you still need to add a lot of substrate to it. It looks like it only as an inch or two in there. For comparison, here is a picture of my 20 gallon tank. The substrate is over half of the tank.


Compare my substrate to yours and you'll see that you need a lot more. In my tank (it's a 20L) I have 4 tiny crabs.

In my above picture, there is about 75lbs (1.5 bags) of play sand and one brick of Eco Earth, plus a little bit of substrate left over from another tank.

Candie wrote:

DragonsFly wrote:I agree with deeper substrate; both fresh and MSW sources need to be deep enough for crabs to submerge (so they can regulate the contents of their shell water); and I would not add more than one additional crab (and a small one, at that). Crabs do "like" to have a buddy, but each additional crab does not just add, but multiplies, the chances of aggression and of molting cannibalism. More is not better, with captive wild animals.

How do they multiply? Isn't is rare to have captive breeding. Anyways I have 2 in a 10 gallon that are completely fine with each other and they do cuddle alot, so I think 2 small ones will be fine since it's a small tank and they do get lonely and travel in packs of a 100 and more in the wild

Yes, as mool said, it isn't the crabs themselves that "multiply," it's the chances of aggression and molting cannibalism. And yes, they do live in large "colonies" in the wild, but animals in captivity do not have all the resources, space, and opportunities that they have in the wild. These animals are used to covering miles of territory every night in the wild. Compared to that, their living space has now been so compacted that (no matter how big your tank is), it's like trying to live with your whole family in, say, your bathroom. You might love your family, but if you cannot ever get away from them, believe me, there will be some aggression. Crabs do not even have all the behavioral options that humans have to ameliorate aggression; and there are further risks, like stumbling across a vulnerable molter underground and deciding, "yum, that's an easy meal" that as humans we don't particularly relate to, but that are just part of what it is to be a crab.

So more is not better, with any captive animal, and definitely not with crabs. Keeping a pair seems to be a good idea, since they do "buddy around" (the longest-lived crabs in captivity were Carol Ormes' pair of crabs, they lived over 30 years with her), but please resist the urge to "collect them all," because, as I said, every one crab you add to the tank (every one animal added to any captive group) does not just add to, but greatly multiplies, the chances of tragic outcomes. (If you want to see a demonstration of the math on that, I'm happy to provide it, it's related to my Masters work.)

And whatever you do, do not add another crab because one is down molting and either you are bored with an "empty tank" (if you only have one now) or you think your other crab (if you already have two) is "lonely" while the other is down molting. They do not experience time the way we do (remember that these animals regularly spend weeks and even months underground alone while molting), and they are well aware that they are not really all alone in the tank when one is down molting. Plus, if you add a new one while one is down molting, the chances of the new one digging down and accidentally encountering the molter (who then becomes a smorgasbord) are very high, since among the first things most new crabs do is dig down (whether to de-stress, or to try to escape, or to molt to try to repair damage done in the "harvesting" and shipping process).

I think 4 tiny-medium crabs in a 20g (long or tall?) is fine. I do have to agree on the subject of sub though, six+ inches makes for a safer molt!! Not all crabs are aggressive, not all crabs are protein-deprived (as I see yours aren't ) and the lonely thing is more of a comfort because it's a familiar convenience they had in the wild. An evolutionary safe-guard, safety in numbers and shell swapping made easier based on the survival of just themselves, unlike in a pack. Somewhere on here it was brought up. Anyways, apologies for my essay explanations (!!) A+ tank decor and happy crabbing!


Twelve PP hermit babies

kornchaser wrote:I think 4 tiny-medium crabs in a 20g (long or tall?) is fine. I do have to agree on the subject of sub though, six+ inches makes for a safer molt!! Not all crabs are aggressive, not all crabs are protein-deprived (as I see yours aren't ) and the lonely thing is more of a comfort because it's a familiar convenience they had in the wild. An evolutionary safe-guard, safety in numbers and shell swapping made easier based on the survival of just themselves, unlike in a pack. Somewhere on here it was brought up. Anyways, apologies for my essay explanations (!!) A+ tank decor and happy crabbing!


Twelve PP hermit babies

Thanks!!!

kornchaser wrote:I think 4 tiny-medium crabs in a 20g (long or tall?) is fine. I do have to agree on the subject of sub though, six+ inches makes for a safer molt!! Not all crabs are aggressive, not all crabs are protein-deprived (as I see yours aren't ) ]

1) If you manage to keep them alive, they don't stay tiny, or medium, or even large. If you intend to keep them long-term, you need to plan ahead to when they are huge. (Our biggest crab went from a largish "medium" size (almost in the "large" range) to a "jumbo" in about 18 months, less than two years, for sure).

2) They don't have to be "aggressive" by tendency, or "protein-deprived," to take advantage of a vulnerable molter. It definitely helps to keep them well-stocked with sources of protein and chitin--they aren't likely to go hunting for their fellow crabs then--but if they happen upon one underground, they won't necessarily "turn up their noses" at it, so to speak.

Four crabs is enormously more problematic than two. If you already have four, that's fine, and best wishes, but if you don't, you might think seriously about stopping at just a pair, or no more than three. Here's the math demonstration I threatened earlier:

1 crab in a tank--no relationships, no interactions (not ideal, because they do like to have at least one buddy).

2 crabs--ONE relationship, one interaction pattern that could potentially cause problems (one chance of molting cannibalism, for example, or fighting over shells between two crabs). But generally, they do get familiar with each other when there are only two, and with plenty of shells and plenty of substrate, it's not an issue.

3 crabs--now you have
A with B, B with C, A with C, and all three together--
FOUR relationships/interaction patterns, not just three.

4 crabs--
A with B, A with C, A with D, B with C, B with D, C with D,
A B and C together, A B and D together, A C and D together, B C and D together, and all four together--ELEVEN relationships/interaction patterns.

5 crabs--
A with B, A with C, A with D, A with E, B with C, B with D, B with E, C with D, C with E, D with E,
A B and C, A B and D, A B and E, A C and D, A C and E, A D and E, B C and D, B C and E, B D and E, C D and E,
A B C and D, A B C and E, A B D and E, A C D and E, B C D and E, and all together--
TWENTY-SIX relationships/interaction patterns (if I didn't miss any).

See how it explodes geometrically? Each time you add just one more crab doesn't just add one more chance for something complicated to happen, it greatly multiplies it. So having just two crabs is simple, interaction-pattern-wise; there's just ONE relationship. Having 3 crabs is actually like having 4, in a way; having 5 crabs is like having 26! If you actually had 26 crabs in a tank, it would be like having a huge, huge colony, with respect to possible interactions--and when it's all compressed into an artificial environment where they don't have the safeguards and all the other limiting (and freeing) environmental factors they would naturally have in the wild, it's a recipe for potential disaster.

Now there are those here who do have large colonies (30-something or more crabs all together), usually in really huge, custom-made tanks with really deep substrate and great attention to minimizing resource aggression, but I think they would all say that they have experienced some molting disasters, for sure, and I'm pretty sure they've all had some molting attack deaths (not just injuries), as well (but correct me if I'm wrong about that, maybe not all of them have, I don't mean to overstate, but certainly some have). My point is not that nobody should ever keep a colony in a captive situation, but that, for the typical crab-keeper, more is not better. It is not better for the crabs to geometrically increase the likelihood of problematic encounters, and it's more than the typical crab-keeper really wants to get into to provide all that they need, when that many crabs get to be jumbo-sized.

Bottom line: if you really want to be able to provide the best possible captive life for the two or three crabs you have now, it's good to resist the impulse to "collect them all," and focus on providing the best you can for those few. If they could, they would thank you for it!

Makes total sense to me!! Even us humans get aggressive when kept together in too large groups for a long period of time haha


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....and get some more sand in that tank! Capt. Jack and any future buddies will need a lot more to do a proper molt. Compare my tank's substrate level to yours. Mine is for 4 micro/tiny crabs.

I have a 20 gallon as well and I'm interested in the clear climber you have. It has the fishnet hanging on it. Where did you get? Or did you build?


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