Why are all the snails climbing up trees?

It poured with rain all morning, so as soon as it stopped we went for a walk up the hill. It was hot and sunny and you could see the steam coming off the ground where the sun was hitting the wet path. We soon realized that every tree we walked past had several snails climbing up it. I can only assume they had come down from the trees when it rained and were heading back up into the leaves now the sun was out. They were all heading upwards and were going really high. It's not something I've noticed before, at least not so many snails climbing up so many trees.

We also found some Jelly Ear fungus (and some snails climbing past it!)

There were a few butterflies out enjoying the sunshine.

Common Blue - showing it's spotty underwings

Common Blue

Large Skipper

Speckled Wood

Then when we got home there was a Small Tortoiseshell in the front garden. This is the first one I've seen for a while, so I assume it is one of the first of the new brood. It's good to see them around again - summer must nearly be here!