HCA: Hermit Crab Association

My largest hermit crab keeps changing shells and then changing back the same night. He’s been doing this for months, I keep buying different shells but he doesn’t seem to like any well enough to switch into.

I have 3 hermit crabs in the tank, large, medium, & small. There’s 13 shells of various sizes and styles. I have 6 or 7 other shells I tried as well that aren’t in the tank right now.

A few days ago I noticed he has a bubble when he shifted shells. Looks like he wants to molt.

Any ideas why he doesn’t like any of the other shells?


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Plasmoc wrote:My largest hermit crab keeps changing shells and then changing back the same night. He’s been doing this for months, I keep buying different shells but he doesn’t seem to like any well enough to switch into.

I have 3 hermit crabs in the tank, large, medium, & small. There’s 13 shells of various sizes and styles. I have 6 or 7 other shells I tried as well that aren’t in the tank right now.

A few days ago I noticed he has a bubble when he shifted shells. Looks like he wants to molt.

Any ideas why he doesn’t like any of the other shells?


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It’s not uncommon for a hermit crab to continuously want to switch shells, mine do it all the time. If you’ve offered many styles and types of shells, then I wouldn’t worry, he’ll eventually settle.

Also, the molt sac doesn’t always mean he’s about to molt, they can have those before or after molts. Those serve as reservoirs for nutritents that help them through a molt.


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How often do you clean the shells?

One other possibility is that he wants the shells, but can’t wear them comfortably because a tank mate got food or sand in them.

Hmmm, I don’t really clean out the shells. I do dunno out debris if I see if in the shells every once an a while. That’s a good point. How should I clean them out? Just rinse with dechlorinated water or do you mean boil them?




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Stella wrote:It’s not uncommon for a hermit crab to continuously want to switch shells, mine do it all the time. If you’ve offered many styles and types of shells, then I wouldn’t worry, he’ll eventually settle.

Also, the molt sac doesn’t always mean he’s about to molt, they can have those before or after molts. Those serve as reservoirs for nutritents that help them through a molt.


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He tries on shells, but always goes back to the same one after a short time. Currently there’s 5 shells his size as well as a couple bigger and several smaller for the medium size hermit crab. The rest are for the tiny guy. Is that enough?




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That’s right around the recommended amount, but more shells are always appreciated.


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Stella wrote:It’s not uncommon for a hermit crab to continuously want to switch shells, mine do it all the time. If you’ve offered many styles and types of shells, then I wouldn’t worry, he’ll eventually settle.

Also, the molt sac doesn’t always mean he’s about to molt, they can have those before or after molts. Those serve as reservoirs for nutritents that help them through a molt.


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Also, I’m
Not very good about the types of shells. Our local pet store doesn’t cart shells big enough for him so I’ve had to buy online. Any specific types I should try? Most the shells I have are turbo I think.


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Plasmoc wrote:

Stella wrote:It’s not uncommon for a hermit crab to continuously want to switch shells, mine do it all the time. If you’ve offered many styles and types of shells, then I wouldn’t worry, he’ll eventually settle.

Also, the molt sac doesn’t always mean he’s about to molt, they can have those before or after molts. Those serve as reservoirs for nutritents that help them through a molt.


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Also, I’m
Not very good about the types of shells. Our local pet store doesn’t cart shells big enough for him so I’ve had to buy online. Any specific types I should try? Most the shells I have are turbo I think.


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I think there is a pomum, nautica / natica, and petholatus, and the green kind that’s kind of like a turbo, though the green ones are smaller really for the medium crab. Also for a while had a filsmentosa and a hexaplex and one that I think is a T. Orbita.


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I have a PP that will not wear anything but babylons. Maybe he wants a slightly different shape one, maybe they are a millimeter too big/small, sometimes they can be very picky like that.

Plasmoc wrote:Hmmm, I don’t really clean out the shells. I do dunno out debris if I see if in the shells every once an a while. That’s a good point. How should I clean them out? Just rinse with dechlorinated water or do you mean boil them?




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A good rinsing with dechlorinated water will normally suffice. Just make sure you get the water in deep enough to clean out the coils. You don’t necessarily have to boil them, but I like to because A) it kills any mold that may be growing inside (from stashed food) and B) the bubbling water gets into the coils, so I don’t have to rinse so thoroughly to get out food and sand.

Some crabbers use shell shops, small containers that keep the shells off the sand. I don’t use one simply because I’m not sure where to put it.

If you’re not sure about good shells, check out the HCA shell guide. viewtopic.php?f=25&t=92552

Okay ~ the picture isn't very clear - but that is not where the molt sac is. The molt sac would be on the other side of your crab.

Sometimes before a crab is getting ready to molt a crab will change into a larger shell before digging down.

Sometimes there can be an irritant in the shell that the crab really wants. Boil all of the shells in freshwater. Then dip them in dechlorinated marine salt water. My crabs love this.

I love my shell shops. By keeping them up off of the sand as others have mentioned, this keeps them cleaner for a little longer than usual.

I have seen them bulk up before a molt so much that all the squiggly ridges on their abdomen are filled tight. It gives the illusion of molt sacs on both sides!

Huh somehow I thought the sac could be on either side. Thank you for correcting me!

Ok so last night I cleaned all the shells and..... my medium hermi shifted shells last overnight lol. Not the big guy yet, but we’ll see.

Thanks everyone!


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