How often to check for pyramidal snails?

[weap0n_X]

I got a 4" Derasa clam about a month ago. I checked, it did not have any pyramidal snails. How often are you suppose to check?

[mbbuna]

if you haven't seen any i would just give it a looking over every 3 or 4 weeks for a few months. if you add another clam check both every week for a few months. make sure you look for them an hour or 2 after lights out