SlugWatch UK is on a mission to discover how widespread the ‘Spanish Slug’, Arion vulgaris, has become since first being identified in the UK in the early spring of 2012.
This species is more damaging than native kinds, and is reported to be strongly resistant to existing molluscicides as well as out-competing native species.
The website provides useful information about slugs and their biology, and provides an identification guide for 18 of the approximately 30 species of slug in the UK. If there’s a weakness it’s that in attempting to simplify matters, the documentation does not make it clear whether there are other species that may readily be confused with those for which pictures and descriptions are provided, and this may lead to unintentional misidentifications. The reality is that some species have to be dissected to get a definitive ID.
The downloadable guide (which is better presented than the one embedded in the website itself) is somewhat hidden, but can be obtained here:
It is, however, not as clear as it perhaps needs to be on the differences between the Spanish Slug and the similarly large native Arion rufus/ater, so further research is advised for anyone wanting to follow up on this project.