HCA: Hermit Crab Association

I have a lone crab (I know they're supposed to be in groups but he's always been alone - I worry that the addition of new crabs will cause more harm than good and I've seen success stories of lone crabs) and he just seems to be sitting on his log in the top corner of his tank and not really moving/eating (it's not a very warm corner either). He's never been a massive eater but sometimes he's really active moving all over the place, climbing the walls and ceiling etc. But he just doesn't seem to be moving much and I'm worried. I've always had a ceramic heat lamp in one corner as his source of heat, but I've just moved house and I was worried he was getting cold so I bought a heat mat instead and stuck it to the back of the tank but the tank doesn't seem to be warm and just seems damp. I've reverted back to his heat lamp to see if that makes him act more normal, but I'm really worried about why he's not moving or eating. Any advice would be appreciated. Thanks!

When did he last molt? Also, PP's seem to do better in large colonies.
I have four currently and they are happy as can be.

He came up from his moult mid June after about a month and a half (I got him in Feb this year so this was his first moult in the time I've known him - I got him from an aquarium I used to work at and I don't think he molted whilst I worked there).
He is a purple pincher, and I know most say they should be in groups but I've also had people say their lone crabs kill any others that come in so I'm worried that it would be more bad than good.

Honestly, there's no actual scientific evidence to support that crabs are social animals. Much of the research suggests that they merrily in groups as a form of protection, as well as being closer to resources (like shells, bigger crabs upgrade leaves a perfectly good shell for a smaller one).

Some of the oldest living crabs in captivity have either been in pairs, or kept solo. And they seem to do fine. So its likely they not as social as previously thought, and there's no suggestion that you harm a crab by keeping it solo or with fewer tankmates.


Heat and humidity plays a big role in activity, do you know what temps/humidity is at?

His temperature is usually in the mid 25 celcius, sometimes getting up to 26 celcius (I'm from the UK so sorry for using celcius!) and his humidity is in the 80's majority of the time, sometimes drops below 80 but I make sure to always keep above 75%. Having recently moved house I did worry that it was colder ambient temperature that may be the issue as he's now placed next to an external wall whereas before he wasn't.

Just in response again to temp, I use a heat lamp normally so it's in the mid 25 celcius in that area but the other corner where he usually sleeps is around 22 celcius which I know is too low. I'm really at a loss as to how to keep temperature steady in all areas of the enclosure, the heat mat I bought didn't seem to do enough it just seems to be warm in the corner where the lamp is.

I have 3 uth on mine! 2 along the back and one on the side. Having 3 gets it plenty warm and allows me the ability to adjust it and just unplug/plug in as needed! I’ve read to keep the uth on the opposite of water dishes and have also read that it’s ok to have a cooler (still warm enough) side and a warmer side of the tank. I keep my thermometer and hygrometer in the middle of back wall and halfway up wall between sub and lid. Curious what the pros say about proper placement for them.

I’m not an expert, just learned a lot here at the HCA. Don’t take my word for it, wait for the expert’s reply...but just wanted to give you a little feedback in the meantime!

Hope you get it all worked out soon!


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Thank you so much for that info, that's super helpful! The tank I've got have 2 heat mats underneath (it was previously used for a gecko) that can't be moved so frustratingly I can't use them! I might invest in some more uth for the winter then! Do you have them all plugged into a thermostat? I worry that if I'm out all day I can't keep an eye on them getting too hot!

I use two heat pads/ UTH'S. I do use a thermostat to keep the temp around 77 to 80 degrees.
https://www.amazon.com/VIVOSUN-Seedling ... 219&sr=8-7 here's one of the heat pads I use: (With a thermostat)
I also use a much smaller one, but there are others you can find on Amazon or online that would fit your needs.

I think a lot of people use thermostats… I just personally don’t. I was able to add the uth one at a time and monitor the temperature to know that it would never go above 81°. Felt like each one only raised it a couple degrees so it was never worrisome, thank goodness!


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