I've got some of the bright red little monsters that have hit me a couple times (ouch) when cleaning, usually hiding under rocks. I have a six line and a melanurus but I've not seen them get one yet. Back in the early 90's I got a bunch of live rock from Hawaii that had some of the variety that get huge. By the time that tank was really mature I was seeing some come out at night that were in the 10-12"+ range. Nasty things that would stand up like a cobra and if bothered would spray some sort of black liquid. Killed some of them but it was my coral banded shrimp that killed most of them. On a couple occasions I saw clash of the titan battles at night. Only wish I had of had video back then.