The blowflies Lucilia cuprina Wiedmann and Lucilia sericata Meigen (Diptera:Calliphoridae) are facultative ectoparasites of warm blooded vertebrates, particularly domestic sheep. Despite being similar in morphology and ecology, the two species and different populations of each species, are known to vary in their importance as pests in different regions of the world. To elucidate the genetic basis of these species and population level differences, flies were collected from sites in Africa, Europe, Australasia, North America and the islands of Hawaii, and examined using a combination of morphology, the random amplified polymorphic DNA technique and a complementary mitochondrial DNA analysis. The results confirm the species integrity of L. sericata and L. cuprina and support the existence of intra-specific genetic variation in L. cuprina, but not L. sericata.