Non-native land flatworms can have a negative impact on local ecosystems, due to their voracious appetites for earthworms or snails. Accurate knowledge on the distribution of non-native populations of land flatworms is necessary to design effective policy to control their spread across Europe. The aim of this study is to address the spatiotemporal distribution of selected species of non-native land flatworms (Geoplaninae and Bipaliinae) in the Netherlands, and provide their current distribution and introduction pathways in a pan-European perspective.

Specimens of Obama spp., Bipalium kewense and Diversibipalium multilineatum were reported across selected Dutch gardens, greenhouses, plant nurseries or garden centers. European distribution of these planarians species was reconstructed using previously published datasets and from records available on GBIF. Morphological species identification was supported by DNA barcoding using a portion of the 28S rDNA marker. Introduction pathways were addressed via haplotype networks based on COI mtDNA.

In total, 27 specimens of non-native land flatworms were collected in the Netherlands. Their different spatiotemporal distribution pattern indicates differences in tolerance to environmental conditions in Northern Europe between B. kewense restricted to greenhouses and D. multilineatum found in gardens. Generally, an increasing trend in the number of records of Obama nungara is observed in the Netherlands and in Europe, with the highest number of records per country reported in France (1.428) followed by the Netherlands (149) and Italy (64). The high numbers of France are, however, artificial and originate from communication towards the public, which has not been as pronounced in other European countries. Genetic analyses suggest multiple introductions of O. nungara in Europe. The combination of morphological and molecular species identification revealed the presence of Obama anthropophila being the first record of this species outside its native range in Brazil. Our results further support the established status of these species in Europe and highlight the importance of citizen scientists in non-native species research.