Indoor hygromiids doing the usual
The land snails in the family Hygromiidae are widespread throughout the Mediterranean countries. Many species in the family have the habit of climbing and aestivating on tree trunks, bushes, stems of grasses, herbaceous plants and on walls.
It is usually claimed that these snails climb on objects to avoid the higher temperatures found on and near the ground in the summer (for example, see Mienis, Pallidula 30:21-22, 2000). That does make sense, but may not be the only answer or the right answer.
Several years ago, I kept several hygromiids in captivity in a large pot filled with soil. The species included Cernuella virgata, Xerolenta obvia and Xerocrassa cretica (below). Because I was aware of their climbing tendencies, I had erected several dry lily stems in the soil. The snails, kept mostly indoors at about 22 ºC and away from direct sunlight, spent most of their active and dormant time on the stems. One December day when it was raining lightly and the outdoor temperature was about 9 ºC, I placed the pot with 6 snails in it outside. About an hour later, 5 of the snails were crawling on the stems and one was on the soil (there was no standing water in the pot).
Xerocrassa cretica: the snail from D28
These observations suggest to me that it isn't just the summer heat that makes these snails climb. Their climbing habit appears to be genetically controlled; they climb regardless of the weather. But why exactly they climb, I don't quite know.