Ten towns in the southwest corner of Poland within 57 km of the German border were surveyed for slugs. Deroceras invadens was found only in the four westernmost towns. In Zgorzelec, which was surveyed more intensively than the other towns, it occurs widely but only sporadically. Although D. invadens had been known in the adjacent German town of Görlitz since 1991, hitherto the only Polish record was from Wrocław, 140 km to the east. This pattern suggests a new colonisation across the border. Amongst the other species, one surprise was the rarity of Deroceras reticulatum in several towns, and another that Arion fuscus was common in one town but not found in any of the others. Records of Deroceras praecox extend its known range in Poland further west. Contrary to expectations from the literature, Deroceras sturanyi was adult in spring and reproducing at a small size typical of Deroceras laeve.