Phalaena degeerella Linnaeus, 1758
Phalaena debornella Scopoli, 1772

Kozlov et al. 2017 divide the present species into three cryptic species (two of which they describe as new): Nemophora degeerella, Nemophora scopolii, and Nemophora deceptoriella. Kozlov et al. 2017 have used a combination of genetic and morphological studies in order to identify characters that separate the three species.

The only reliable and diagnostic morphological character that separates the species is apparently the size and shape of the male (but not the female) labial appendage; unfortunately the authors do not include illustrations of these differences in their paper. There are no differences in male genitalia. Other characters that mainly concern wing size, shape and colouration are very difficult to assess. They do not on their own and not in all cases discriminate between the species and, in addition, I cannot confirm their validity from the specimens shown in Fig. 7 in Kozlov et al. 2017. For example, the distance between the outer edge of the cross-band on the forewing and the beginning of the black stripes in the wing tips is said to be larger in Nemophora scopolii than in Nemophora degeerella. This is indeed true for the N. scopolii specimen shown in Fig. 7D, but the N. scopolii specimen shown in Fig. 7E has the black stripes joining the outer margin of the cross-band. Thus the distance is zero and the specimen could be identified as Nemophora degeerella.

The species apparently differ in a short stretch of their COI gene („DNA barcode“), but several other genetic markers, especially when analysed together, do not separate between the species. A genome-wide analysis of single nucleotide polymorphisms using the ddRADseq method discriminates between the two species N. degeerella and N. scopolii, but the significance of this result is unclear, because only four individuals (2 of each species) were used, thus limiting the outcome of the phylogenetic analysis to only a small number of possible fully-resolved trees and thus also drastically limiting any statistical validity of the dataset. Ideally, analyses of this kind should include hundreds of individuals (see Peterson et al. 2012).

In summary, the evidence for the presence of cryptic species within the taxon Nemophora degeerella is weak, but I provisionally adopt the concept of three cryptic species by Kozlov et al. 2017 until more information on the validity of the concept becomes available. Of the three species, only two are reported from Germany, Nemophora degeerella and Nemophora scopolii, whereas the third species, Nemophora deceptoriella, is apparently restricted to the Caucasus region.