I have had 3 blue serpent stars that have harmed nothing for the 8 months I've had them. I've read here that they are predatory, but have not lost a fish, snail or crab to them. They came in about 4" and are now 6-8". They hang out in the LR with their tentacles up like antennae and reach from around the LR for the shrimp, mussel and squid I chop and sprinkle where they hang out. Like damsels, I'm sure there'll be the folks who scream that they are murderers in the waiting, but I have not had any livestock losses to them in my 125g reef tank. I keep them with a bluefin angel, red spotted hawk, 2 blue and 3-3stripe damsels, a lawn mower blenny, a yellow tang and a mystery wrasse, a 6 line wrasse, about 200-250 hermits, 3 peppermint shrimp and a bunch of cerynth and turbo snails. And 2 emerald crabs.