A reliable determination of Hydrotaea borussica females, and of females in closely related species, has so far not been possible as a range of criteria, some contradictory, has been ascribed to their identification. The DNA sequence of H. borussica is identified to enable the assignment of females to males. In addition, the DNA sequence of H. meridionalis is identified for comparison with H. borussica, and the DNA sequence of H. pandellei determined for intraspecific comparisons. The yellow colour of the abdomen, regardless of its extent, and the two dark shiny dorsolateral third tergite patches reported from various females have little or no taxonomic significance in these flies. Existing identification keys are inadequate for distinction between H. borussica and H. meridionalis females; a considerable number of Hydrotaea females may have been incorrectly assigned to species in collections. Identification criteria for females of Hydrotaea borussica and similar species are re-evaluated and a revised evidenced-based key to these species (albeit based on a limited number of specimens) is proposed.