Why are most of my snails doing THIS?

[sbube]

As you can see in the picture below, I have 4 Tarebia granifera snails that have decided to take up residence above the water line in my tank. They adhere to the glass with a little moisture between it and their shells. The one on the left has been right there for about 6 days. The one next to it joined a couple days later, and the other two assumed position a couple days ago. This tank has been established for a couple of months.I don't know if they're committing hara kiri or what, or whether they're still alive. They never move or go back down into the water. The water adhesion seems to almost dry out at times but then later I see it has been renewed - whether because of condensation or them making water seep out from inside their shells. The shrimp seem to be doing well. In the picture you can see a shrimp trying to prevent a fifth one from going up there (just kidding).

[Erlina _rusli]

Mine did the same thing when water has evaporated and some algae left on the wall above the water line, but it only happened early time after i introduced the snails into my tank

[Mustafa]

Not sure why some snails do this, but just push them back into the water if they aren't actively eating and just kinda hanging there almost "lifeless". Otherwise they'll dry out.

[sbube]

Yeah, it turned out two of them died dried, and I pushed the other two back down and they seem fine. Are these snails too dumb to even have self-preservation instincts?

[Varanus]

They don't usually stay out of the water long enough to die, at least in my experience, so maybe there is some special factor involved when it does happen.