The northern distribution limit of Dermacentor marginatus in Central Europe: New observations, data gaps and impact of erroneous reports

The current state of knowledge regarding the northern distribution limit of the ornate sheep tick Dermacentor marginatus is presented using a distribution map of Central Europe. The map extends from eastern France to western Ukraine and shows that the northern distribution limit is approximately at a geographical latitude of 51° N. There is a 400 km wide strip north of the Alps in the center of the map where no occurrences of D. marginatus have been documented, yet. The first few mappings of D. marginatus in eastern Austria are a small contribution to closing this data gap. However, it is also pointed out that erroneous data from citizen science projects, together with an uncritical application of species distribution models (SDMs), have led to an increase in the publication of unrealistic occurrences of D. marginatus up to 55° N and beyond. Furthermore, these erroneous data and the resulting incorrect distribution maps undermine the validity of climate-related projections regarding the future occurrence of D. marginatus. It is recommended to refrain from using unverified Dermacentor records, especially those from NABU/naturgucker-the original source of these erroneous tick records-for scientific applications. Instead, researchers should rely on expert-validated data or supervised citizen science platforms with strict quality control.