I don't know much about them. But I don't think they really eat anything, they will latch on an invert or fish, suck some blood, swell up, then stop. They don't really kill/eat unless the fish or invert is really weak possibly or is infested with leeches resulting in weakness. I am not sure they are really effective at attacking fish. I think they are slow and latch onto things like snails or, like I say maybe sick or weak inverts/fish. But there are some leeches that are plant leeches. To be honest I don't know a lot about them.
