Disappearing snails?

Authors
Adrian T. Sumner
Issue
15
Page
3

David Long (Mollusc World 14, p. 21, July 2007) asks if anyone else has noticed a decrease in snails sieved from leaf litter this year. As I have never been an enthusiastic siever (in my hands it turns out to be a lot of work for very little reward), I can’t answer this directly. However, I have got the impression that certain species do seem to be adversely affected by weather conditions. Back in 2005, on one of the field excursions organised by the Lothian Wildlife Information Centre, I was asked to show a newcomer “that snail that smells of garlic”. Easy enough, I thought, but in fact I was completely unable to find a single specimen of Oxychilus alliarius that day, and in my part of Scotland it seems to have remained quite scarce ever since. The same applies to Vitrina pellucida, which again I thought was common enough, but recently has been difficult to find. 2003 was a very hot and particularly dry year, and my guess is that this could have been detrimental for many species of snails, perhaps the small ones especially. It might be interesting to compare pre- and post-2003 records to see if there are any other species that do feature less frequently post-2003. However, as David implies, it would be important to monitor the same sites year after year to establish if there are any significant changes. Even then, as we know, the weather at the time of the survey can have a profound effect on what we might find, regardless of any longterm changes.

Interestingly, just a few days before writing this, I was recording molluscs in Edinburgh, and found both Vitrina pellucida and Oxychilus alliarius without any difficulty. It looks as if the wet summer had revived both species.