Snails in summer

As I was driving along the countryside in the limits of Zejtun I came across these weird masses of white shelled snails on top of stones and poles. These creatures are really weird. With the onset of summer they enter a period of inactivity known as estivation. They find the highest possible places so as to avoid damage from high temperatures of summer. Doesn't the heat of the sun bother them when they are under its cruel mercy? They're lucky that they've got white coloured shells but I still cannot understand how they survive the intense heat of our Maltese summers! Instead of finding places in the shade they suction themselves to the walls, dry branches or poles and retreat into their shells. Thus protected, they wait until the weather becomes more suitable.