Background: Obama nungara is a species of land flatworm originating from South America; the species was recently described and distinguished from a similar species, Obama marmorata. Obama nungara has invaded several countries of Europe, but the extent of the invasion has not been thoroughly mapped. Methods: In this article, based on a five and a half-year survey undertaken by citizen science, which yielded 530 records from 2013 to 2018, we analysed information about the invasion of Metropolitan France by O. nungara. We also investigated the variability of newly obtained cytochrome c oxidase 1 (COI) sequences of specimens from France, Italy and Switzerland. Results: Obama nungara was recorded from 72 of the 96 Departments of Metropolitan France. The species is especially abundant along the Atlantic coast, from the Spanish border to Brittany, and along the Mediterranean coast, from the Spanish border to the Italian border. More than half of the records were from an altitude below 50 m, and no record was from above 500 m; mountainous regions such as the Alps, Pyrenees and Massif Central are not invaded. Local abundance can be impressive, with 100 of specimens found in a small garden. An analysis of our new COI sequences, combined with published sequences of specimens from several countries, confirmed that three clades comprise the species. The first clade, ‘Brazil’, is currently confined to this country in South America; the second clade, ‘Argentina 2’, was found in Argentina and in Europe, only in Spain; and the third, ‘Argentina 1’, was found in Argentina and in Europe, in Spain, Portugal, France, UK, Italy, Belgium, and Switzerland. This suggests that two clades of O. nungara from Argentina have invaded Europe, with one widely spread. Discussion: The present findings strongly suggest that O. nungara is a highly invasive species and that the population which has invaded several countries in Europe comes from Argentina. The wide dispersion of the species and its reported local abundance, combined with the predatory character of the species, make O. nungara a potential threat to the biodiversity and ecology of the native soil fauna in Europe, and probably the most threatening species of all invasive land planarians present in Europe.