Thats a good point acyually...I habe never actually seen my polka-dot loaches eating a snail (although I know they do because they keep dissapearing) but I think they eat the smaller ones whole and then larger ones they suck the snail out and leave the shell. I am not certain this is correct but if you visit loaches online - http/www.loaches.com/ - then you may be able to find your answer!
Im not sure about them eating my snail though. My dojos are 4 1/2 inch and 5 inch and my snails opening is 1 inch. Too big I think. The snail also has a trap door. Anyone here have dojos co-existing with snails?