I have never had that problem with my orchids, but to get rid of snails in my fish take, I just drop in a couple of pennies. I think it is the copper that kills the snails. I am not certain how it works, but a pet store owner told me about it and it worked for my fish tank. It took awhile, but they all died and no more hatched out. Not sure if this will help with your orchids, but maybe a starting place.