HCA: Hermit Crab Association

Hello everyone! I know I haven't been active on here after joining, sorry about that! I do have a question that's concerning me though.

So, a bit of backstory (skip to the next paragraph if you don't think the backstory will be useful), I have had three medium PP hermit crabs for about a year, and earlier this year, I upgraded them from a 10g to a 20g (long). Last week, I went on vacation and purchased three medium-large hermit crabs from a shell shop (they have amazing looking crabs, an amazing selection of shells, and are far more passionate about their crabs than any other pet store I've gone to). Anyway. These hermit crabs were together in a large (maybe 4g?) Kritter Keeper container for a few days before I brought them home. They were in the container with 3-4 shells in case they wanted to change as well as having a bowl of freshwater (it was only for a few days so I could get them home and get them saltwater) and a bowl of food (a variety of veggies, fruits, and meat).

Anyway, upon bringing them home, I carefully checked for mites and then placed them into my established crabitat and carefully supervised them. One of the new ones, Gilbert, seemed to fit right in and made himself at home. The largest new one, Clifford, lumbered off into one of the hides. However, the final newest one, Beast, became a problem immediately. He went into one of the hides and tackled one of my original hermit crabs, Superman. There was a struggle, and I thought I heard a faint chirping and so I got Superman and put him on the other side of the crabitat. I hoped that would be it, but it was not. Beast retreated back into the hide, and then when another one of my original hermit crabs (Georgie) strayed past the entrance, Beast grabbed him and dragged him into the hide. I spritzed them and Beast let go. I then removed Beast back into the Kritter Keeper and placed five shells ranging from his current shell size to slightly larger. I thought perhaps that the issue was that it was a shell fight, but that was a couple days ago and he hasn't shown much interest in anything but hiding in the iso (Kritter Keeper). I reintroduced him today to the main crabitat and he went back to that same hiding spot, where Clifford was. Clifford is larger than him, so he couldn't do much to him, but I still moved Clifford anyway so I could carefully observe Beast. The best way to describe Beast's behavior is that he's acting like a trap door spider. He looks very tense and waits at the entrance of the hide before attempting to tackle any crab that goes by. I'm not sure if he's pinching at them or even trying to rip the shell off, just that he's grabbing them. Is this normal? Is there anything I can do to fix this? I'm going to Petco and maybe Petsmart tomorrow, so is there anything I should buy?

Tank Specs:
20g Long
6" play sand/EE mixture
Saltwater dish (large enough for the crabs to submerse themselves in) - spring water mixed with IO aquarium salt
Fresh spring water dish
Food includes various veggies, fruits, meats, oats, peanut butter, and honey
Countless hiding spots
25-30 spare shells ranging from the same size as the smallest crab to larger than the largest crab
Heated with a heat mat to 80F and maintained with a thermostat
Humidity is kept at 80

The iso tank has sand in it as well, in case I forgot to mention. Oh, and also, I will be upgrading the crabs to a 46g bowfront in the near future, I just need to replace the light bulb in it and rehome the fish I was breeding in it. Hence why I got so many crabs.

Can anyone please help me?

I don't know if any of my very old posts about captive populations, the geometrically increasing likelihood of aggression with adding even ONE new crab to an established population, or any of that are still around. :/ If you like, I'll pm you with my phone number, because I can explain in detail much more quickly than typing.

Very quickly: this is to be expected; your tank is tiny (for animals who are used to MILES of range), and adding new members to any established group (no matter the size of the habitat) is virtually certain to be stressful for everybody and to cause some aggression. You can either let them work it out and see what happens, keeping conditions good and LOTS of extra, APPROPRIATE and appropriately-sized-opening shells in there, or separate them into two groups and leave your established group alone (they have already figured out how to live with each other in captivity, as best they can) and let the newcomers figure that out as well in their own new digs.

Had you asked me beforehand, I would have said it's not a great idea to add newcomers to your established group. Three is plenty for a captive bunch, more than enough in a 20g, and plenty to deal with as they grow (you could potentially end up with six baseball-sized crabs 30 years from now, that's going to be more than most people would really like to be getting on with). I know it's a huge temptation to want to "collect 'em all!"--and you hear a lot about how "social" they are, and how they live in huge groups in the wild--but captive wild animals have a lot of intense pressures that do not exist in the wild, and we need to take those into account as we move forward trying to give them the best possible lives they can have now.

Anyway, yes, the options: leave them alone with best possible resources you can provide and hope for the best--or separate them back into their two groups. If you go with option 2, and at some point you decided to upgrade to a MUCH bigger tank--like a 75 or preferably, a 90g--you could then put both groups in at the same time; it wouldn't be anybody's established territory and you might have better luck with them ALL being "new kids on the block" together.

Best wishes; I know it's upsetting and scary to see them unhappy and even aggressing against each other. It will work out eventually, one way or another.

Sorry, I missed your note about upgrading soon. Although a 46g bowfront is not as big as I would wish for 6 crabs that are all medium to large, I would definitely recommend you keep your two groups separate for now, and then put them all in the bowfront when it is ready; if it were me, that is what I would do, to minimize (although it still may not at all eliminate) the pressure toward aggression.

(Again, if you want more detailed notes on why my recommendations for numbers are smaller than other recommendations on the board, I'm happy to explain, but it's just an even LOOOOOOONGER post than I already posted here.)

DragonsFly wrote: ↑

Fri Sep 20, 2019 3:18 pm

Sorry, I missed your note about upgrading soon. Although a 46g bowfront is not as big as I would wish for 6 crabs that are all medium to large, I would definitely recommend you keep your two groups separate for now, and then put them all in the bowfront when it is ready; if it were me, that is what I would do, to minimize (although it still may not at all eliminate) the pressure toward aggression.

(Again, if you want more detailed notes on why my recommendations for numbers are smaller than other recommendations on the board, I'm happy to explain, but it's just an even LOOOOOOONGER post than I already posted here.)

Thank you for your advice! In case I forgot to clarify, Gilbert and Clifford merged into the group very well, there was only one problematic crabby. He's still being a bit antisocial, but I just saw him have a quick antennae battle with another crab and that was the end of their interaction. Hopefully, he won't take it any further. Still, I'm going to rehome the fish tomorrow and order a light fixture for their tank soon, so I can begin moving them.

Additionally, if they did become baseball-sized, I would most definitely invest in a much larger tank, I don't mind upgrading as I go along.

Yes, eventually (if they survive), they do get that big, and then you'll need huge tanks and very deep substrate, etc.--but that will be a while.

Yes, I saw that there seemed to only be an issue with this one crab, but you never know how things will go as things continue. Sometimes, just one of the animals in a group "acts out" the stress that all are feeling; sometimes it may be that there is only one who is particularly freaked out, and the others are not as stressed; and sometimes the others are even MORE stressed, but their response is to keep away from others and not confront. There are lots of behavioral options.

If they are just bopping each other with antennae, that is definitely not a battle, that's just them getting to know each other--like dogs sniffing each other. A fight is when they actually grab at the other with a pincher and try to shake the other or tear bits off . Certainly moving into a larger tank should help to relax some of the pressure they are feeling. Bear in mind that adjusting to the new tank MIGHT bring up odd behavior and even possible aggression again--because significant changes always come with stress, even if they are good changes--but again, it should settle down as they figure out how to live in this new tiny world.

Do resist the urge to "collect" any more though! I know it can be strong, but you be stronger!!!