Hehe I generally let nature take it's course in my tank. Obviously if I had some expensive fish goin "fin to fin" (haha get it?) I'd have to do something about it. Crabs will take advantage of easy and small prey and it sounds like your snails fell into that category. I have the extra large turbo snails which have been uneffected by the hermits and my emerald for that matter. You'll find out soon enough though that not everything is willing to cooperate with your vision on how you'd like your tank to work out. Good luck though and don't get discouraged.