It's hit or miss. I had two of them in my 55g for a while. One was about 8" and the other was like 3.5". I got the larger one about 3-4 months prior to getting the smaller one. When the smaller one went in, they squabbled for about two days, and then proceeded to share the same cave, poking heads out at the same time. It was very cute, unfortunately, the smaller one got a little too curious next to a 1,000 gph ph and found out the hard way that it was a bad idea :(. One of my personal favorite fish. It's a riot to watch him grab a hermit and pull it down into his cave, then a minute later you see the hermit come trudging out, in a huff. Then, to the hermit's dismay, the engineer grabs him again haha. Very comical :mrgreen: