During the course of having the 75 gallon tank I’ve now had 2 blue knuckle hermit crabs. The first one lived for just over 2 and half years. After he died, there was no crab in the tank at all for a few months. Now, recently, I have added more crabs again. In the mix of the new batch is a small blue knuckle hermit.
The first one I had lasted a long time. He got to be quite large for a hermit crab. He was so large that when I got my new hermit crabs they all seemed surprisingly small. I hope my new blue knuckle hermit gets to be as large as the first one. He needs to grow to be about 2 inches if he’s gonna fill the shell that the original blue knuckle hermit used to use.
In my experience, the blue knuckle hermit likes to climb on everything in the tank. It will suspend itself upside down on live rock. It will climb steep slopes on underwater structures. It will fall from time to time. Sometimes I hear “clunks”, only to glance at the tank and see the blue knuckle crab has just fallen off a high perch on some live rock.
I haven’t seen any of my blue knuckle hermits kill or even battle with any other aquarium inhabitants, so I’ve never had to deal with hostilities. Tangs even liked to eat algae off the top of the first hermits shell. The hermit didn’t even flinch or try to hide.