The Harlequin ladybird Harmonia axyridis Pallas, native to eastern Asia, is an invasive, nonnative species that has recently achieved an almost worldwide distribution. A conspicuous feature of this species is colour polymorphism of the elytra. In its native area, the populations consist of a recessive nonmelanic morph, several dominant melanic morphs and small numbers of other (rare) morphs. The morph proportions in native populations have been intensively studied and vary with geographic area, climate and time. In contrast, colour polymorphism in invaded regions has been little studied. We examine and try to account for the morph frequencies observed across the different invaded regions. In America, monomorphic populations consist of the non-melanic morphs while European populations contain also melanic morphs. In particular geographic areas of Europe, the average percentage of the non-melanic morphs varied between 78 and 99%. It was highest in the lowlands of northern Italy and central and northern Europe and decreased in the Alps and western (Spain, UK) and eastern (southeast Russia) margins of the recently invaded area. In central Europe the frequency of the nonmelanic morphs decreased over the course of the year