Irish Yellow Slug or Green Cellar Slug is a common garden species, often found - like in this case - under rotting logs. Originally native to Crimea and the Black Sea area it is believed introduced to Ireland in the 17th century and then on to UK is 20th century. In the UK, Limacus maculatus seems to be replacing the Yellow Cellar Slug (Limacus flavus), itself a 17th century import to UK from Eastern Europe, across much of its range.