Scale insects are frequent invaders. With 129 established species, they numerically represent one of the major group of insects alien to Europe. Scales are usually small insects with wingless females. Due to this small size and concealment, many species, mainly belonging to the families Diaspididae, Pseudococcidae and Pseudococcidae, have been accidentally introduced to Europe, mostly originating from tropical regions and essentially from Asia. The trade of fruit trees and ornamentals appears to be the usual pathway of introduction. At present, alien scales represent an important component of the European entomofauna, accounting for about 30% of the total scale fauna.