Hałaj R., Osiadacz B. (2017): Woolly ash aphid -is the alien bug posing a threat to European ash trees? -a review. Plant Protect. Sci., 53: 127-133.Prociphilus (Meliarhizophagus) fraxinifolii (Riley, 1879) (Hemiptera: Eriosomatidae) is an alien species in Europe that has been spreading quickly there. This paper presents the origin and current occurrence, classification, description, identification, and biology of this species. It also discusses the harmfulness and threats, especially the impact on hostplants and ecosystem, invasion rate and facilitating factors.