I know they're a problem in florida as I kept getting em sizes as grapefruits in my collection nets, and I just put one in and it devoured a plant in the bucket within a hour.
I know that theres a problem with VHS and the fish-
I forgot what its spelled but the DNR is so darned strict making us kill minnows and clean the boats really good when fishing. Maybe the snails are part of why? Im not sure if its the carrier of that virus. or its just plainly unrelated.