Xeropicta derbentina is a land snail native to the coastal areas of eastern Mediterranean. It was introduced to southern France in the 1940s and it has since spread to most open habitats in the region of Provence by both active and passive dispersal. Like many other species in the family Hygromiidae, this species also has a habit of climbing on vertical surfaces prior to estivation. Aubry et al. (2006) demonstrate that when estivating snails are dislodged from their perches, they quickly climb up the nearest vertical surface. If that surface happens to be a parked car, the snails are in for a potential ride to uninvaded territories.
The table below from Aubry et al. (2006) shows the number of Xeropicta derbentina detected on cars at 7 parking lots in Provence.
The authors note:
That the countryside in Provence is heavily populated in summer possibly influences the efficiency of this passive dispersal mechanism. Indeed, the colonization of tourist areas in Provence seems to confirm this hypothesis, because X. derbentina populations are frequently found restricted to car parks when the surrounding habitat is unsuitable (e.g. forests, mountain grassland) or when colonization is recent.
Aubry et al. 2006. Active and passive dispersal of an invading land snail in Mediterranean France. Journal of Animal Ecology 75:802-813.