HCA: Hermit Crab Association

My largest crab has been jumping in and out of 2 shells. He really seems to like one of them but it's too small and the other one is just big enough for him to retract all the way into but for some reason he goes back to his smaller one lol. Sometimes he changes in and out many times a day! It's funny but I'm thinking I need to find him that just right shell to.move into. I have others in the tank for him but they might be slightly too big. He's a very picky crab lol

You could always try boiling the shells in water to clean them. Or at least rinse them out! They could have sand or something in them. Or holes or other imperfections. Or maybe he just needs to change shells, but doesn't have enough options to find one he really likes.
If you wanted to, you could measure his size and then measure the opening of the shells. That would help determine the problem... Or at least rule out shell size as an issue!
Making sure the shells are the clean, the right size, and the right type would all help!

or even a different type of shell, i have one crab that likes the jade shells now and will only go for those and the others like the natural turbos and one that will take anything that is left..and if I put other shells in there they might look at them and change but they will hurry and go right back into their original shell.

Definitely check the type of shell. Maybe he likes the type of shell he currently has, and is just unhappy with one of a different type. So, if it's not the same type, try getting others of the type he likes best.

I boil the shells I put in the tank and periodically boil them to keep them clean. I have measuring calipers and have spent some time and money finding shells that are of similar type/shape of the shell he's fond of. I also filed any rough edges down until smooth and inspected the shells for holes or chips. I'm thinking I need to find some more he might like but I've went to every pet store in the area with no luck (they always have too small or too big shells). Ordering online is kinda difficult because I like to see the shells in person but it looks like it'll be my only shot at this point lol. I do find it kinda funny when he jumps in and out of this two shells though. At least he feels comfy enough to try different ones on.

typeAnd the 2 shells he jumps in and out of are the same type of shell

It's not too unusual for them to be indecisive over what feels better to wear. They factor in a lot of different things when choosing a new shell - weight, smoothness, shape, etc - and each shell is going to be slightly different than others that are the same size and species. Eventually he'll settle on one or the other, or if you add more he may choose one of those instead.

I have one that finds the shell he likes and sticks to it, and the other changes every day, sometimes more than once. She's been switching back and forth for the past week between two polished turbos. They are the same opening size, and I think she just likes them equally well, and since there aren't any other crabs in the tank right now that want that size shell, when she's in one the other one is always available, and it's just as good, so she goes back and forth. In the wild, as soon as she was in the one shell, the other one would be taken, so she wouldn't have that option, but here she has the luxury of two equally good shells. I expect the same thing may be happening with your crab--even though they are different sizes, they may be equally good for other reasons (one's smaller but feels maybe more sturdy, the other one is larger but maybe it's just a bit too heavy, or something). Or it may indeed be that he really would want one just right in the middle of those two sizes, and you don't have one of the type he would prefer in that size. I'd see if maybe you can find him one of his preferred type in that in-between size, but in the meantime, I don't think it is a bad thing in and of itself for him to keep switching, as long as he's not hanging out naked. After all, there is not an awful lot to do when you're stuck in a tank; changing shells is something. . .

Sometimes I wonder if I'm causing extra stress by having so many shells available. I just added about 10 shells to my cage for my two crabs, and both have been going through every single one. They even switched into each others shells, and ones a PP and the other is an E, so that was kind of mind blowing to me. Prior to this, I had maybe five shells in there for them, and they picked one and stuck with it.

My point is that in the wild, they wouldn't have this many shells. I wonder if we're kicking their instinct into overdrive, like an OCD impulse.

I worried about that too, and I do think it is a valid concern. If you only have two crabs, I think you can make do with much fewer shells. However, for the people with lots and lots of crabs together, it is important to provide a large number of shells to avoid shell fights. Basically, they are wild animals in an artificial environment now, and that IS going to cause changes in behavior, if not full-blown pathological behavior. Like any zoological exhibit of captive wild animals, you just have to balance the factors present in your particular population. Like I said, if you only have two and they all get along well (or are very different sizes), you probably don't need to provide a large number of shells all the time.

Okay, thanks. They seem to have found shells they like (they haven't changed in 24 hours), so I'm going to take most of them out, but I'll leave their old shells in.

I don't leave my shells in all the time, I take them if they are not interested in them and then maybe in a month or two i will clean them up & throw them in, if they change fine if they don't I take them back out.. I alway make sure there are shells in there if I have molters come up

I leave a shell shop full at all time, and I notice they change when I don't even notice. I also notice they change shells more often in the shell shop then shells on the ground.

I've had 1 crab for 5 months, 3 crabs for 4 months, 5 crabs for 3 months, and 6 crabs for 2 months. Making 6 now.

Here's my statistics for shell changes so far.
I only have 1 crab still in the original shell, and she just came up from a molt since i saved her, and she still fits her shell, it's a nice one.
I've watched 5 of my crabs switch shells in person, and of those 5, 4 of them have changed 2-3 times for weeks or months.
And shell fast switches I've seen about 18 times in person.

So I can only imagine how many times they are tyring on other shells at night. The shell shop is trashed EVERY morning. Which means there is shell action every night.

I switch the shells with new ones every couple weeks and i clean out the shell shop. After I do this, I'll find 2-3 crabs in there shell shopping. They use it as a bathroom and a place to sleep.

I will always promote having a shell shop full time.

Hermit crabs are just so darned silly. Sometimes, they'll change shells 3 times a day for weeks on end, then they find one they like and won't change for a year!

They seem to go shell crazy when they first get home, and after a few months they just kinda take them for granted. The only time I get shell changes now is if I get a new crab or a new shell.