Snails in a jar

22nd March 2009, Sunday

TV over the past month or two has been awash with shows on Charles Darwin, with quite a bit of repetition, but one new project I learnt about this week concerned an Open University mass participation project to study the evolution of colour patterns in two species of banded snails.  These attractive molluscs will be familiar to gardeners.  The idea is to determine if historical banding patterns across the country compare with what is present at the moment, and determine if the banding pattern may possibly be evolving due to changes in numbers of predatory thrushes and climate change for instance. Always keen to have a go at simple recording projects I logged on to the website and then got searching in my embarrassingly weedy garden.

 

There are two species of banded snail in Britain. Cepaea nemoralis, the larger of the two species, reaching a shell size of 20-24mm and possessing a dark lip to the shell (the lip is the edge of the opening to the shell which is swollen in the adults). Cepaea hortensis is smaller,  with a shell 17-20mm in size, and with a pale lip. Uprooting clumps of grass in our border, and turning over stones, I rapidly found 50 banded snails, no wonder song thrushes have been visiting our garden so regularly this winter!  Flushed with success I retreated to the computer to analyse and record my haul. This was when I discovered that only the adult snails are required, as the young animals – with a fragile and unswollen lip to the shell, cannot be so easily told apart.

The website is helpful, taking you through identification and has a useful quiz to test you are identifying the relevant colour patterns. Snails may have a yellow, pink or brown ground colour, with numerous, single or no dark bands, so with two species there is scope for a lot of different categories. Separating the brown and pink ground colour on the quiz proved to be a little tricky at first, but with 5 minutes practice I was getting the questions on the website 100% right.

So on to my snails. All my adults turned out to be Cepaea hortorum, all had a yellow ground colour and half had no bands. The remainder had multiple dark bands. Interestingly the younger snails that I discarded seemed to be predominantly multi-banded. I will repeat my sampling later in the year to see if I can get a larger sample.

All in all an interesting way to learn about snails, and you can visit the website to compare your discoveries with what has been recorded in the past, although the RX area seems to have been poorly surveyed. Give it a go and add to the data for this large-scale evolutionary experiment.