The northern bark beetle (Ips duplicatus), in Europe originally restricted to northern countries, expanded its distribution range to eastern Europe in the 20th century and is now causing considerable damage in spruce forests. In the past decades its presence has been confirmed in several Central European countries. By means of pheromone traps and visual inspection of infested logs, in this study we demonstrate that I. duplicatus is also present in the Rhine valley in Switzerland and Liechtenstein. Breeding galleries with beetles and exit holes in an infested spruce log indicate that the trapped beetles had successfully developed in a local stand nearby. An inquiry addressed to European entomologists was carried out to obtain information and references concerning the year of the first record or mention of I. duplicatus in their respective countries. This information substantiated the expansion of its historical range to the southeast in the middle of the last century and clearly showed recent movement westward, with Switzerland and Germany currently the westernmost countries where this species occurs. This recent range expansion is likely attributed to the transport of infested timber. The economic significance of this expanding bark beetle species is discussed in view of its co-occurrence with the notorious pest species I. typographus.