I was hitching my way across the country and pitched my tent behind a Husky station in Sault Ste. Marie. There was a terrible storm and I woke up to discover a foot of water rushing into my tent. Turns out I had camped in the middle of a seasonal lake. I barely made it to shore, and in the morning I had to wade out into the lake to recover all my belongings. Since everything was thoroughly waterlogged, I spread it all out on bushed and tree limbs to dry in the sun. I came back about an hour later and discovered that everything I owned was absolutely covered in a seething mass of slugs and snails, hundreds and hundreds of them.
So my guess is you’ve probably gotten a lot of rain and it’s flooded them out of the ground where they usually live.
On the bright side, they are probably quite edible. I hitched a ride with a French chef shortly after that snail/slug episode and he was disappointed I hadn’t collected and kept such an unexpected bounty. He told me when he’s out camping, he snatches any slugs or snails he finds and just sticks them on a rock right beside his camp fire until they sizzle and then he pops them in his mouth and eats them.
The survival book I use on the road says slugs and snails of all sorts are edible, but recommends that you starve them for 24 hours before eating them to allow them to digest anything they’ve recently eaten, so that you don’t end up accidentally ingesting poison oak or something. The book recommends stew as a good way to eat them. If you use the beer trick people have described, they’ll already be marinaded.