How many species?

Obviously, if I’m going to attempt to see every single terrestrial snail in the UK, I need a complete list of all the species so that I can:

  1. Target particular species to search for
  2. Tick them off as I go along

However, I have found it a mite tricky to find a single document that has all this information in the same place. The best I have found online is Roy Anderson’s ‘Annotated list of the non-marine Mollusca of Britain and Ireland’. However, the issue then becomes: What counts as a terrestrial snail?

On the surface this sounds like a very easy question to answer. Surely a terrestrial (or ‘land snail’) is a snail that lives on land? Well, yes, but there are grey areas. For example, species such as the Dun Sentinel (Assiminea grayana) live on saltmarshes at the high tide mark. Are they a land snail that lives on the edge of the sea, or a sea snail that lives on the edge of the land?

To answer this question I looked at another text: Robert Cameron’s ‘Land Snails in the British Isles’. This was the book that first got me interested in snails, and I’m happy to go along with its division between ‘land snails’ and ‘not land snails’. I copied out a list of all the species in the book, which yielded exactly 100 species, a delightfully round number.

But then I noticed something. In 2014 I had seen an introduced population of the Turkish Snail (Helix lucorum) in Hertfordshire – but this species wasn’t in the book. Clearly, the species had only been so recently discovered in the UK that it couldn’t have been included. I added it to the list, yielding 101 species.

However, I was now concerned that there may be other species I had failed to include. I went back to Anderson’s list and double-checked. Sure enough, I found a section entitled ‘Hothouse Aliens’ which included several terrestrial snails that were omitted by Cameron. I added these to the list, bringing the total up to 111.

I then checked the marvellous ‘An illustrated guide to the land snails of the British Isles’. This included a species called Pupilla pratensis, a species only confirmed as occurring in the UK very recently. 112 species. It also had another hothouse alien – Kaliella barrackporensis. 113 species.

Finally, I read through several years’ worth of articles on the ConchSoc website. Here, I discovered a 2009 reference to the discovery of some empty shells of a snail species in the Granaria frumentum-illyrica group. As far as I can tell, these two empty shells are the only record of this species from the UK. Nevertheless, I added to the list, bringing the final total to the 114.

114 species. 365 days. That means that I need to see a species of snail on average every 3.2 days throughout 2015. Possible? I suppose we’ll find out.

I’ll post up my target list tomorrow.

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