Pom pom crab question

[Fizzman]

I bought 2 and now only see one. My friend bought two and only has one too. He bought a new third one, haven't asked if it's still alive. The question is, do they fight and kill each other off? I don't think it died cuz I saw both for the first 2 weeks and both look healthy. Don't think it was eating cuz both would be gone by now.

 

[JMLewis]

I've had 2 for a couple years now. Sometimes I think ones missing but always shows up. They both come out every time I feed reef roids. Love these guys!