Never had one eat hermits or the larger ornamental snails. Small pyramidal snails are on the menu. They forage from LR, specifically small crustaceans, but nothing that would grow into something remarkable. Larger ones, and ones that are well established can be tyrants to smaller, peaceful fish, but it depends on the personality of the individual. I'm on my third one. First was great, second was a jerk, and this one is a good size, bought from another hobbyist as it was pestering his other fish. It's been a model citizen in my tank and has not bothered anyone. Just squared off with my two damsels in the first few minutes and now all is well. They are very pretty fish and add a good deal of color and movement. Just be aware of the potential risks, particularly if you have smaller fish.