Changes in habitat suitability for the tick Ixodes ricinus (Acari: Ixodidae) in Europe (1900-1999)

Climatic changes may lead to drastic changes in the distribution of arthropods important in human health. We tracked changes in habitat suitability for the tick Ixodes ricinus in Europe from 1900 to 1999, using a geographically extensive gridded climate data set. For the whole period, 52% of the territory was always unsuitable for the tick. In the grid, 6.11% of the cells were classified as having a deterministic drift with positive trend and 7.4% as deterministic drift with a negative trend. A total of 17.25% of cells were classified as exhibiting a random walk behavior, with a trend to increase of habitat suitability (9.57%) or decrease (7.68%). Zones of deterministic trend extend into most of Ireland and parts of the United Kingdom and France. Total and summer rainfall primarily drive changes in habitat suitability in these sites. Areas of random walk are common in Scandinavia, central Europe, and the Balkans, with summer rainfall and temperature largely directing the changes. Sites of reported increased abundance of L ricinus coincided with areas of increased habitat suitability over the last 20-30 years, but this feature showed a long-term random walk negative trend. Habitat suitability for I. ricinus remains relatively stable in Europe, with no sites showing permanent changes in habitat suitability (negative to sustained positive or vice versa). However, some zones in the continent showed a clear trend to increase or decrease.