Members of the family Cimicidae (Heteroptera) are obligate haematophagous ectoparasites. The Cimex pipistrelli species group parasitizes on bats, the likely ancestral hosts of the whole family. Based on morphology, it was suggested that three species of the group were present in the West-Palaearctic region, although their validity remained a matter of discussion. Surprisingly, the status of these species has not been studied from the point of view of host specificity. We examined the diversification of the species group using morphological data, including the putative diagnostic characters, and sequences of one mitochondrial (cytochrome oxidase subunit I, COI) and four nuclear loci (internal transcribed spacer 2, 18S and 28s ribosomal genes and elongation factor 1 subunit α). This was carried out on a sample of 225 individuals from 69 bat roosts and 44 mist-netted bats, altogether representing 12 bat species from 13 European countries and Lebanon. We revealed 27 mitochondrial haplotypes representing two distinct haplogroups and one outlying haplotype. The extent of morphological variability of specimens representing both haplogroups covers the range of characters reported for all three recognized species; therefore, the haplogroups clearly do not correspond to any described species. Also, the very limited variability found in the nuclear sequences of the cimicid bugs examined suggests that separate species do not exist in the region. We found considerable morphological differentiation among samples from different bat species, although individuals representing particular mitochondrial haplogroups often live sympatrically and on the same host species. It seems that batbugs are morphologically adapted to a particular bat host despite the low genetic structuring among individuals parasitizing different species of bats.