JohnK How about taking some more pix and doing another post featuring them. See this also http://molluscs.at/gastropoda/terrestrial.html?/gastropoda/terrestrial/enemies.html

Interesting. I’ve seen snail shells with a hole punched through the center swirl of the shell that I assumed would be cause by birds. These look whole-vacated-move out of-evicted-forclosed. Odd. Then I found this quote,”Snails will come out of their shells to mate. All land snails produce both male and female sex cells, but they cannot self-fertilize, and so need a mating partner. Most land snails perform some sort of courtship ritual lasting anywhere from one to 12 hours before any actual mating occurs, and will remain outside of their shells for this entire process.” Have you looked beneath the deck? For more info on why snails leave shells and party beneath the deck see this link http://www.ehow.com/about_6599004_do-snails-come-out-shells_.html

One expert says it could be critters in the tree above this spot eating and discarding snails. Some birds eat snails.

After pondering this and doing a little searching, I agree with Shannon. I’d go for birds perching in the tree above the steps and dropping the shells. I read one report that song thrushes have been known to do this.

It’s probably a chipmunk or two having some snacks.

I don’t have a clue! Never seen anything like it.