Three-band Gardenslug Lehmannia valentiana
Even though it is not absolutely certain this is Lehmania valentiana, experts think it most likely is. This is a southern species which used to be very rare in the Benelux. But nowadays it regularly pops up in gardens and parks. It is a relative of the Great Slug, but rather indistinct and pale. This species seems to conquer the world quickly: it has already been found in Eastern Europe (Poland, Lithuania), Russia, China, Northern America (Missouri), Central America (The Dominican Republic) and even South America (Colombia). Recently it even turned up in Britain.