I put 3 in a couple days ago. The shrimpies picked on 2 and they died, Oscar and Van ate them. The 3rd died a day later, same thing I think. I don't know fully.Not a crawly but you might try a live clam.
I should try again, at 3am, and put it opened, in the back of the tank behind Octo Rock.
I'm 70% sure, Loc is back there. The scarlet shrimp are clinging to the screen (we have over the top of the tank to octo proof it) at the top of the tank, and they do that when there is a ceph OR they're picking on the algae.