DNA barcoding identified the eggsac parasite as Sarcophaga sexpunctata (Fabricius, 1805), a widely distributed flesh fly known to parasitize eggsacs of different spider species. We screened 10 expanding and nine native populations for S. sexpunctata infections. Of nine screened native Italian populations, all showed infections. We estimated the abundance of S. sexpunctata infections in four of these populations. Between 30% and 90% of all eggsacs were parasitized, on average 50%. At the same time, none of the 10 analyzed expanding populations from the Baltic States and northeastern Germany were affected by brood parasitism. Inquiries with fellow arachnologists did not reveal any incidence of parasitism in additional expanding populations in Sweden and northeastern Germany (Jonson and Friman pers. comm.).