Climatic and anthropogenic factors shape the Asian range expansion of the invasive slug Arion vulgaris.

The Spanish slug Arion vulgaris is one of Europe's most problematic terrestrial invaders yet, its distribution beyond the continent has remained poorly resolved. Outside Europe, the species has only sporadically been reported from North America, the Caucasus and a few isolated sites in the Southern Hemisphere, and its presence in most of Asia has been considered unlikely by previous climate-only models. Here we combine targeted field surveys, integrative taxonomy and ensemble species distribution modelling to reassess the extra-European range of Arion vulgaris and to understand how climatic and anthropogenic factors jointly shape its invasion potential in Asia. We provide the first reliably documented record of Arion vulgaris in Central Asia, based on concordant morphological and COI-based genetic evidence from a population in the northern Tien Shan. We then construct a global niche model for the Arion vulgaris-Arion rufus-Arion ater complex using climatic predictors and land-cover fractions representing intensive agriculture, mosaic agro-natural landscapes and urban areas, and analyse predictor importance and partial dependence across a grid of Asian subregions with a European control area. Climatic variables dominate the overall model, constraining the broad potential range of the species, but in Central Asia, including the Western, Northern and Central Tien Shan, urban land cover emerges as a key predictor, allowing high predicted suitability in settlement mosaics embedded within otherwise climatically marginal mountain and continental environments. Compared with climate-only projections, our model substantially expands the area classified as suitable in Asia. These results imply an ongoing and largely undetected eastward expansion of the Arion vulgaris-Arion rufus-Arion ater group and highlight the need to interpret niche models in the context of land-use patterns when assessing invasion risks and potential impacts on endemic montane faunas.