A large part of eukaryotic genomes is composed of inactivated mobile elements (TEs for Transposable Elements), corresponding to remnants of ancient waves of TE invasions. TEs also play a very important role in adaptation to new ecological conditions. The most famous example is the industrial melanism of the peppered moth: the black color has been shown to result from the insertion of a transposon within a gene. Considerable progress in sequencing approaches now makes it possible to assemble TE-rich regions within genomes. We found that a TE of the helitron type secreted in the genital fluid of a parasitoid wasp is present as identical copies in the genome of 5 Lepidopteran species sequenced by the Darwinian tree of life project from specimens collected in UK, suggesting a recent wave of introduction of this TE in Lepidoptera. We hypothesize that increase of parasitoid introductions worldwide could, as for viral infections, increase the rate of TE invasions, and play a role in populations decline. We recently amplified the helitron from specimens collected in France indicating that the spread of this TE is not limited to UK. We will map the extent of the invasion in the geographical range of the species Pararge aegeria and Polyommatus icarus, in particular in areas where these species have been recently introduced such as Madeira island (P. aegeria) and Québec (P. icarus) since founders of the current populations could have been introduced before helitron spread, thus allowing an approximate dating of the epidemic.