You know, I do have a few of the snails in the pics above. According to the thread posted afterwards, they will devour plants. That may be what's causing some wisteria leaves to surface quite frequently.
Purely speculation here, but I've noticed orange stains in my bath tub, toilet, and porcelain sink in the bathroom. This could either be iron or copper stains. If it's copper, then maybe my water changes are keeping the more vulnerable, younger snails at bay.
Time to get copper and iron test kits, if I'm going to keep the apple and ramhorn snails.