Green Snail Dormancy (Aestivation)
The higher temperatures of summer are not the only cause of dormancy in green snails. It is also caused by factors such as daylength, so the snails will become dormant even if the soil is cooled by irrigation.
When preparing for dormancy, green snails seal the opening to their shell with a solid skin (see first image below). This skin is dissolved when the snails reactivate.
Near Cobram, as the snails have approached dormancy they have also tended to darken in colour, making them more similar to common garden snails (see images below).