What are these snails doing?

[PigletJohn]

I find small yellow snails walking around on top of my box hedge after rain, in daylight. I do not see them on dry days.

Snails love wet surfaces. If you dribble water down a wall, you can get a snail to climb up it (following the trail of water). I guess they are feeding on something - either the leaves (softened by rain) or some kind of surface algae?

Banded snails! They're so pretty. They have tendency to come out en masse when the moisture levels and temperature are just right. Much like Goldilocks, appropriately for their colouring.
I've seen them eat mostly eat algae and lichen, never had a problem with them eating nice plants.

Surely they are plotting to take over the world, but they come out in the rain as they believe the human race melts when they get water on them after they saw one scene of the wizard of Oz....