Stigmella naturnella (Klimesch, 1936) (Lepidoptera, Nepticulidae) a fast-spreading European leafminer of Betula, with a revised key to linear leafmines on Betula

Stigmella naturnella (Klimesch, 1936), a leafminer of Betula, is here recorded as new for France, Croatia, Ukraine, Belgium, and the Netherlands, Since 2018, it has expanded its range into the last two countries, partly based on numerous online observations. Its distribution history is reviewed, the species is diagnosed and its life history is described. A lectotype is designated for Nepticula naturnella Klimesch, 1936. The species is widespread in the Palearctic, from Japan to the North Sea, with a maximum of 1.63% variation in its DNA barcode. Legacy leafmine records for Germany are reviewed, resulting in the confirmation of its occurrence in Baden-Württemberg already in 1935, but other old records are rejected. It is one of the few Nepticulidae species that hibernate as adult, a possible contributing factor to its expansion. As the leafmines may be confused with other Betula mining species, a revised key to the leafmines of European Stigmella species on Betula is provided. Stigmella glutinosae (Stainton, 1858) and S. alnetella (Stainton, 1856), usually feeding in Alnus, are both recorded to occur occasionally on Betula and are included in the key.