Wildlife on Walls: 4. Garden Snail, Helix aspersa

The recent hot, dry spell has triggered some distinctive behaviour in snails that helps these moisture-loving molluscs survive long, dry periods.

It's called aestivation and involves the animal secreting a thick layer of mucus that cements the mouth of the shell to a hard substrate, minimising water loss. 

The shady side of an old stone wall with plenty of gaps between the rocks is the perfect place to aestivate through a drought and numerous snails often pack themselves into these crevices, until the classic British wet summer returns. Like many invertebrates, the internal organs of dormant snails shrink substantially once they've sealed themselves in their shell and stop feeding.