First records of the "nigrovittata" colour variety of Philoscia affinis Verhoeff, 1908 (Isopoda: Philosciidae) in Belgium and the Grand Duchy of Luxembourg

Philoscia affinis Verhoeff, 1908 is a terrestrial isopod that shows remarkable variation in its color pattern across Europe, however the natural populations occurring in habitat in Belgium, the Grand Duchy of Luxembourg and the rest of northwestern Europe are from one typical brown mottled form. The recent increase in records of a new color form in Belgium is striking. This different color form closely matches the variety from Italy originally described as Philoscia muscorum affinis var. nigrovittata Verhoeff, 1908, herein referred to as “nigrovittata”. All recent observations of this form in northwestern Europe are associated with synanthropic habitats. We therefore hypothesize that these populations are introduced via soil or plant trade from the south and that the northwestern European typical form of Philosica affinis is still an indicator species of ancient forest in Belgium and the Grand Duchy of Luxembourg. The sharp rise in records and the numerical dominance of this variety over native species in colonized habitats warrant close monitoring.