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.

The Benefits of being Hermaphrodite

It's seed-sowing time again - a time of hope and expectation, tempered only by the knowledge that the garden snail population is waking up too, ready to chew its way through all that tender new growth. Some time ago I devised a way of reducing the garden snail population by giving them somewhere to spend the winter where they could easily be found (click here) and then transported into the countryside. These two, caught in the act of mating, are a couple that I missed.


Garden snails Helix aspersa are hermaphrodite but nevertheless exchange sperm, as these two are doing. Being hermaphrodite is one of the secrets of their success because it means that every individual in the population can lay eggs and produce offspring; if animals exist as separate genders, either male or female, only half the population can lay eggs.


Click here to see some images of snail eggs and click here to see the baby snails that emerged from them.

Snail in a Hurry

A few days ago Ron Bloomquist published at interesting photo of a ‘hiccuping’ intermittent snail trail on his Walking Fort Bragg blog, and was wondering how it might have come about (see http://walkingfortbragg.com/2009/07/so-how-foggy-was-it.html) .This snail wandered across my path today and this series of photos shows quite nicely how hit moves, with a head-to-tail wave of muscular contraction along its foot which is slightly arched – check out the way the gap under its foot moves backwards as the snail moves forwards in this top-to-bottom sequence (double-click the images for a larger, clearer view). It occurs to me that if the snail was crawling along a hot road surface and wanted to minimise the exposure of its foot to the heat it might well arch its foot even more, and might leave a trail like the one Ron saw...........just a thought.