I was walking in my friends pecan field this morning. Well anyway, I came across these snails, thousands of them. My friend had irrigated his field a few days ago, and the snails were only in the leftover mud. Any that were on dry land appeared to be dead or dying. They were also inside an irrigation ditch just above the water level. Any ideas on what they are? One of the snails has mud all over it's shell, those are not spots.