How many species is a species? Integrative taxonomy sheds  light on the systematics of an insular beetle species complex  comprised of twelve subspecies (Coleoptera: Tenebrionidae:  Dailognatha quadricollis)
Diversifications driven by intricate geographic structure, especially those associated with insular systems of continental origin, pose major challenges for investigating taxonomic boundaries. The present study focuses on Dailognatha quadricollis, a group of darkling beetles riddled with a tangled taxonomic history due to its insular nature and complex diversification across the Aegean archipelago. For the first time, the taxonomic status of the twelve subspecies assigned to D. quadricollis is revised under an integrative framework, utilizing genome-wide SNP data in combination with morphological characters and geographic information. Congruence among alternative species delimitation methods supports the subdivision of D. quadricollis into three species, resulting in the following taxonomic changes: Dailognatha quadricollis (Brulle) (= Tentyria laticollis Besser syn. nov.), Dailognatha carceli Solier stat. resurr. (= D. quadricollis anaphiana Koch syn. nov., = D. quadricollis sporadica Koch syn. nov.), Dailognatha rugata Solier stat. resurr. (= D. obtusangula Reitter syn. nov., = D. quadricollis montana Koch syn. nov., = D. quadricollis plicata Koch syn. nov., = D. quadricollis pseudobtusangula Koch syn. nov., = D. quadricollis rhodica Koch syn. nov., = D. quadricollis samosana Koch syn. nov.). The present study demonstrates the taxonomic utility of characters not previously studied within the group (including genital morphology and mesoventrite punctation), providing redescriptions for the three delimited species, plus Dailognatha hellenica Reitter. These findings highlight the value of integrating genomic, morphological and geographical data when delimiting cryptic lineages across discontinuous topographic landscapes, while also raising important questions about the systematics of insular species complexes comprising multiple subspecies.