snails will eat whatever they can get there teeth into (do they even have teeth?). They'll eat left over fish food, aswell as any type of green vegetable, such as cucumber, lettuce and spinach.
Snails are eating machines. They eat everything. Different species show preference for certain things though. They can reak havoc in a planted tank though. Are you trying to keep some alive or get rid of them?
Snails almost exclusively eat vegiation. often detritis often plants. Just plant as broad a crossection as you can and say thank you to them for the ones that thay leave you. Again a little fruit or veg is often welcome but dont remove the old plant debris as this may well be a favorite. If thay become T O O numerous (thay are not JUST eating machines) Then clown loaches are good at keeping numbers down in fact most BOTIAs will do a good job. If you want to keep them then AVOID Botias.