HCA: Hermit Crab Association

Hi guys. One of my hermit crabs came up from molting (I assume) after about 2 months buried. I went to change out the food and found him in a MASSIVE shell that was in there more for decoration! He moved it across the tank, but I'm worried he might be unable to switch to a better shell. Also, why would he do this? Will he be able to get to the food? Right now I have him surrounded by a bunch of reasonable sized shells.

He was originally in the shell on the left. He's now in the green shell on the right.


You can just barely see him in the green shell.


See the big hole? That's where I found him, underneath a hide.


The white shell is another one he has used periodically, before he went down to molt.


One more view. Sorry the pictures aren't great quality.



1. What kind of substrate is used in your tank and how deep is it?
Sand and coconut fiber, a little over 8" deep.

2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?
I have three gauges. Two measure both temperature and humidity, and one it just temperature. I move them throughout the tank. It stays from 72F to 84F, and 70-90% humidity. Recently it's stayed at 76F in the cooler side and 79F at the warmer side.

3. Is a heat source used in the tank? If so, what?
I have an Ultratherm heat pad on the back and a very low wattage blue reptile night bulb at the top.

4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?
Both are available. I use instant ocean salt and seachem prime dechlorinator. I use 1/2c salt per gallon.

5. What kinds of food do you feed and how often is it replaced?
I feed fresh food every day and dry food every few days. I'm still trying to get a routine down for food. Here are some of the things they get: dried meal worms and shrimp, zoo med fruit mix, calcium supplement, various organic fruits (dried and fresh), fresh vegetables, cooked ground turkey, egg shells, peanut butter, coconut, peanuts, baby food (organic vegetables/fruits and water), and a dried mix that they absolute adore. I'm not sure where it came from, but I got it with my first crab.

6. How long have you had the crab and what species is it, if known?
I have had this crab for about 4 months. I believe PP.

7. Has your crab molted, and how long ago did it happen?
Just came up. He went down about 2 months ago, as soon as I moved him into his new home. He was previously in a 10 gallon, which I realized was way too small for him.

8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
It's a plastic tote, 30+ gallons. 26"L x 19"W x17"H

9. How many crabs are in the tank and about how large are they?
There are 4 crabs. One small, two medium, and this guy, who is probably a big medium.

10. How many extra shells are usually kept in the tank, if any?
They have about 25 shells, which I'm continuing to add to, so that I can rotate them in and out.

11. Have there been any fumes or chemicals near the crabitat recently?
Nope.

12. How often do you clean the tank and how?
Everything is cleaned with water before it goes in. Spot cleaning is done with water (dechlorinated).

13. Are sponges used in the water dish? If so, how are they cleaned?
Nope.

14. Has anything new been added to your crabitat recently?
Nope.

15. Is there any other information you would like to share that might be helpful (anything that is regularly part of your crab care, playtime, bathing, etc.)?
I don't think so.

16. Please describe the emergency situation in detail.
See above.

They are the shell experts, we are definitely not!

What we think of as "way too big" may be "just right" for a given crab. Also note that the OPENING size, which is what the crab thinks of as the "size" of a shell, is NOT directly correlated with the overall size of the shell. For example, looking at the murex (the spiky shell) and the polished turbo side by side, the opening size is not hugely different, although the polished turbo looks a lot bigger overall.

In addition, PP's love polished turbos. Once mine had access to those, they "never looked back." I had one try a magpie (like the black-and-white one you have in there), but she only stayed in it a day or two, and it has never been used since, either by our three resident crabs or any of the rescues that have come through (which is sad, because I think those are beautiful, but apparently the crabs don't care what I think about "crab fashion"). Once they have the option of polished turbos, that's it, that's the ideal shell, as far as they are concerned. So, it may be that even though that one seems "too big" for you, since it is polished (and therefore lighter than it would be if it were the same shell but unpolished), and since it is a turbo, your crab just said "hallelujah!" and moved in.

Finally, since the only ways to get a crab OUT of a shell that it WANTS to be in are cruel and likely to damage or even kill the crab, you are just going to have to "like it or lump it." As long as the crab is "crabbing around" normally, I'd say "more power to him" and enjoy that he has chosen that lovely shell.

P.S. If you are really worried about him being able to get around, get some more polished or semi-polished turbos, with opening sizes about that size and graduating down to somewhat smaller. I can't be sure, but just from the shells I can see in your pics, it looks like that is the only turbo in the tank, and that may be why he chose that one instead of the ones you think are a better size for him. If there were other, smaller turbos (with OPENING sizes between that magpie's opening size and the opening of the turbo he is in now), he might be happy to switch to one of those. But like I said, if a turbo is available (especially a polished or semi-polished one), they will pretty much grab that one over any other type of shell.

Final thought: He definitely look "ambitious," way back in that shell, but maybe he's planning to do back-to-back molts and knows he'll be a lot bigger next time. Our biggest crab went from a smallish "large" size crab to a "jumbo" in about three, pretty much back-to-back molts. So they can grow fast, sometimes.

Thanks for your response. I feel much better. I've got him surrounded in shells right now. Unfortunately most of my turbos are either too small or too big, I think. Hopefully I can get some new ones soon. It's a lot easier to find <1" opening turbos, but he's way too big for those.

Yes! You may being experiencing the same problem I've had, which I believe resulted in our first-ever aggression crisis: we have plenty of shells, LOTS of polished or semi-polished turbos, BUT there is a gap of opening sizes, which I had not really noticed until this crisis happened. We have tons of turbos with openings up to and including 1"; and lots with openings of 1 1/4" or more, but almost NONE in sizes in between. And 1/4" sounds like a TINY measurement to humans, but in fact, if you compare a turbo with a 1" opening to one with a 1 1/4' opening, there's a HUGE difference in overall shell size. We needed turbos with 1 1/16", 1 1/8", and 1 3/16" opening sizes. And I still have not found any to fill that gap!

I do not know why there is a major deficit in turbo shells in between those opening sizes, but when I frantically tried to order some to fill in that gap, the first place sent me a bunch of shells with opening sizes all under 1" (they were measuring the "opening" as the full visible underside of the shell, not the "use-able opening" that the hermit crab cares about). When I contacted both that place and two other places, nobody had any available in that opening size gap (if measured correctly with calipers).

If anybody has any shells with those opening sizes (by caliper measurements) that your crabs have outgrown and you no longer need, I would definitely be interested in buying them! Sounds like milliepinta might want some, too!

Normally I'd say trust in the crab, but honestly I'm not sure he will be able to move in that giant thing! There is so much weight to that type, and he's not a very big hermit. I would recommend propping the shell so the opening is exposed just in case he needs to slip out and can't lift it up enough himself. Has he managed to move it at all?

Well, he's disappeared again today. I'm not sure if he's in the same shell or a very similar shell. The flipped over shell is empty. There was a similar one next to it, possibly a bit smaller (but still HUGE), so he may be in that. The food dish has a lot of sand and is really picked over, especially the chicken baby food. At least he got a good meal He did initially drag the shell about 18" in straight line from it's starting location yesterday, so he's definitely capable of moving, although probably not easily. Crazy crab. Good thing I got a 40 gallon breeder tank from the petco sale. I wasn't planning on setting it up right away, but I may have to if he stays in a giant shell.





Bonus adorable crab who spends all day in the moss pit. I think the other two guys are buried somewhere, so he's all alone today.

There is a smaller green turbo missing from the new photo, unless you had removed it. He should have a much easier time now!

Yea he must have switched to a smaller green turbo because there were 4 and now there are 3 green turbos...unless like wodesorel said, you took one out.

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