HCA: Hermit Crab Association

Hello, everyone. I've been an HCA reader for more than a year and a half now, and I decided to take the plunge tonight and join the club in order to run this past you. Since my question pertains to behavior that I should watch out for, this seemed the appropriate forum in which to post it.

There's some ancillary backstory here, but I'll just jump right to the relevant bits. I've had Buster (PP) since February of '18. He had a tankmate for a couple of months, but said tankmate died for ultimately unclear reasons in late April or early May of '18. He's been alone ever since, and while he's been by all accounts flourishing (three successful molts!), the whole "hermit crabs are communal" thing kept tickling the back of my mind. Weighing the ethical implications against Buster's psychological well-being, I broke down and bought him a new roommate today: Johnny (also PP).

Johnny was free of mites and appeared to be in good health, so in keeping with what what I've read here, I didn't quarantine him; instead, I gave him a brief bath--fifteen to thirty seconds of full submersion--in Primed freshwater and put him right in with Buster. The enclosure, for the record, is a 20L with six inches of sand/EE in a roughly 5:1 ratio with ideal temperature/humidity levels, fresh- and saltwater, places to climb, hide, etc.

Johnny is smaller than Buster, but I didn't realize how much smaller until I got him home and saw the two of them side by side. Eyeballing the crabs and using the sizing chart as a guide, I'd say that we're talking about a small-and-a-half and a teeny now cohabiting. Everything that I've read here indicates that small crabs and big crabs can live together, but since Buster was by himself for so long, a part of me worries that he's "forgotten" how to be sociable and will bully the new guy. I've seen it emphasized in various posts here that aggression and dominance are different, so my question is this: what are some signs of aggression that I should watch for?

As I write this, the two of them have been together for almost four hours, and I've seen the following behavior three or four times from Buster: he climbs on top of Johnny, holding him in place while his antennae go bonkers checking him out. There has of yet been no attempt on Buster's part that I've seen to use either his big or small claw to get Johnny out of his shell or otherwise harm him, and I've heard no chirping from either of them. I broke them up the first time that I saw this, but I let them be on the subsequent occasions, and each time, they eventually went on their separate ways. They're sitting next to each other as I type this, and they seem to be getting on fairly well, so am I correct in not being too concerned right now?

I know that I can't watch them 24/7, so I want to minimize the chances of anything tragic happening during this get-to-know-you period. In your experiences, are there any special measures that I could or should take?

Welcome to the board. Glad you could make the piunge!


Did you dip them both in the same water to make them smell the same - or the new guy in the current freshwater pool in the crabitat so he smells the same as the older one.


Honestly, it just sounds like your older one is just checking him out and letting him know who is boss - establishing a hierarchy. As long as they dont get vocal, it's a sign that it's going well and in the next couple of days, much of that behaviour should pass.

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Thanks for the welcome!

I didn't think to dip Buster as well before introducing the new guy, nor did I bathe Johnny in the existing water pool. What I did was the following: I put a couple of inches of water from the gallon jug in which I make all of their freshwater into a container outside the crabitat, bathed Johnny in that, and then placed him inside the 'tat. My rationale for this was that while he appeared to be free of external parasites, the bath might reveal some that I had missed: creepy crawlies floating in the water = isolating him until that problem gets resolved. Since everything looked good, I put him right in with my existing crab.

The first thing that I did after waking up this morning was check on them. Buster's out and about, but there's no sign of the new guy. He's a small crab, so I figure that he's either hiding in a spot that I can't see from outside the enclosure or he's buried himself, but I'm obviously not going to start rooting around for him until I have an ironclad reason to do so. I did have a brief freakout when I saw what I initially thought was a piece of severed limb and presumed that Buster had mutilated his new roommate during the night, but it turned out to just be a bit of kidney bean that one of them had pulled out of the food dish.

Thank you for the reassurance; I'll continue to keep an eye on them.

It's been a few days since I introduced the newbie, and I wanted to give a quick update.

As far as I can tell, Johnny is acclimating remarkably well. He changed shells within twenty-four hours of being added to the crabitat, and he seems content with his choice. He's a very inquisitive little crab; I've seen him investigate both water bowls, and he finally figured out today that he can climb on the big piece of cholla that I have in there. He's constantly going into the food dish to nibble on things--sweet potato and dried coconut appear to be particular hits. I might want to get a bigger dish, though--one that could comfortably accommodate the two of them if they decide that they want to eat at the same time.

The behavior that I described from Buster has decreased dramatically, if not ceased entirely. If nothing else, I haven't witnessed it in over a day, and Johnny is showing no obvious signs of physical distress. I've seen them make eye contact without incident, and the two of them have even taken to sharing one of the 'tat's hides.

Knocking on wood and crossing my crossables, it's looking as though this will be a smooth transition.