...............................................................................................................................................3 Introduction..........................................................................................................................................4 The invasion process − preventing impact of invasive species .......................................................5 Evaluating the invasive potential – pest risk analysis......................................................................6 Snails as invasive species.................................................................................................................6 The Spanish slug (Arion lusitanicus) invasion, and a possible successor?......................................7 Purpose of the thesis ........................................................................................................................8 Cantareus aspersus; general biology................................................................................................8 Materials and methods .......................................................................................................................10 International invasive overview and invasive traits .......................................................................10 Current nonnative climate and future scenarios.............................................................................10 Danish populations and invasion history .......................................................................................10 Field survey of C. aspersus population metrics .............................................................................11 Distribution data analysis...............................................................................................................12 Active dispersal..............................................................................................................................13 Statistical analysis ..........................................................................................................................16 Pest risk analysis ............................................................................................................................17 Results................................................................................................................................................18 International invasive overview.....................................................................................................18 Current nonnative climate..............................................................................................................20 Invasive traits .................................................................................................................................20 Danish population and invasion history.........................................................................................21 Distribution area.............................................................................................................................23 Population metrics .........................................................................................................................23 Land use patterns ...........................................................................................................................25 Active dispersal..............................................................................................................................26 Pest risk analysis ............................................................................................................................29 Discussion ..........................................................................................................................................32 International invasive overview and nonnative climate.................................................................32 Invasive traits .................................................................................................................................32 Danish population and invasion history.........................................................................................33 Distribution and population metrics...............................................................................................34 Land use patterns ...........................................................................................................................35 Active dispersal..............................................................................................................................36 Pest risk analysis ............................................................................................................................38 Conclusion and perspectives..........................................................................................................41 References..........................................................................................................................................43 Appendix I..........................................................................................................................................50 Appendix II ........................................................................................................................................54 Appendix III.......................................................................................................................................67 Appendix IV.......................................................................................................................................73 Appendix V........................................................................................................................................80