New records of the spiny-cheek crayfish Faxonius limosus (Rafinesque, 1817): expansion in subalpine lakes in North-western Italy

We report the first occurrence record of the spiny-cheek crayfish Faxonius limosus in two North-western Italian lakes: Orta and Mergozzo. We also confirm the occurrence of the species in Lake Maggiore. Faxonius limosus is native to the east coast of the USA. Since the end of the 19th century, it was introduced to Europe, where it rapidly spread in Poland, Russia, France, and Germany. In 1991, it was recorded for the first time in Italy in Lake Iseo (Lombardy region; NW Italy), and soon it has spread in Northern and Central Italy. Although Faxonius limosus is included in the list of European Union Concern, only two reports suggested the occurrence of this species in lakes Maggiore, Orta and Mergozzo, but these were never confirmed by experts. The aim of the present paper is to shed light on the distribution of F. limosus along the coasts of the three North-western Italian lakes. To this end, we used visual census and trapping to detect the occurrence of F. limosus, providing also georeferenced and environmental information of its habitat. We discovered 31 new occurrence localities (18 municipalities) for the species, scattered across the three lakes. These new findings highlight the urgency of implementing monitoring and management programs to prevent F. limosus spread and to mitigate its potential ecological impacts.