Kept one of these for a few years. Aggressive little sod. He would attack your fingers while you were cleaning the tank. I checked where he was one day, before cleaning, and I could see a blue shell in the corner - so I happily start cleaning the other end of the tank - and then I see him 3" from my hand, claw ready, and realise he has shed his shell, and it was the empty shell at the other end of the tank