Dikerogammarus villosus (Sowinsky, 1894) (Crustacea, Amphipoda, Gammaridae) for the first time in Italy

The recent discovery in Lake Garda, and in other watercourses of northern Italy, of Dikerogammarus villosus, an amphipod crustacean from the Ponto-Caspian region, is a worrying confirmation of how it is rapidly spreading in Europe. In Lake Garda, the species is present, with high population density, in the southern basin, where it is the only gammarid of the littoral benthos, and in the northern basin, with lower population density, where it still coexists with the native species Echinogammarus stammeri. Ovigerous females and juveniles are present most of the year in all the explored areas. Considering that the species has often replaced the native gammarids in invaded waters in most European regions, we want to raise the alarm for a possible progressive elimination of the native species E. stammeri by the invading one from the Garda littoral benthos.