Dark Meadow Grass-miner Elachista freyerella

Formerly placed in the genus Cosmiotes along with two closely-related species, Southern Grass-miner Elachista stabilella and Meadow Grass-miner Elachista consortella. Formerly given the vernacular name Broken-barred Dwarf.

All three of these former Cosmiotes have increased significantly in Norfolk in recent years, although this one perhaps less so than the other two. They can often be picked out as a group by the presence of a patch of white scales in the apex of the forewing, though that may not be completely reliable and doesn't help if the moth is too worn.

Of the three, stabilella is the only one to have white frons and head, however this is not always pure white, and the frons at least can be grubby whitish on the other species, at least vaguely so. So far as I know, freyerella and consortella (and stabilella if the head is not clear, such as on worn individuals) can only be separated from one another by examining the genitalia and even then they can be difficult. The freyerella below showed greyish scales on the top of the head but the frons was pale buffy which at a stretch you might describe as whitish. A poor quality photo taken with flash could exaggerate this, so considerable care should be taken if relying on head colour for identification.

With males, separating freyerella from stabilella using genitalic characters is really tough. MoGBI describes some differences but these are not fully supported by the accompanying diagram nor by images in the Moth Dissection website. It is easier to identify male consortella using genitalic features (though still quite small differences).

In view of that I was pleased that the following specimen was a female - very unusual in my experience of Elachistids. Females are more easily identified using genitalia, with differences in the antral region and the signum in the corpus bursae. In freyerella, the scelerotised section of the base of the ductus bursae/colliculum is much longer than in consortella and more even-width, tapering more gradually, than in stabilella. The diagrams in MoGBI also show differences in the extent of spiculation in the sternite covering this area. Of the three, freyerella has the largest signum. On stabilella, the next largest, the outer points point down not straight out opposite each other, and there are no tiny points at the bases of the four larger points as in freyerella. MoGBI also shows stabilella as having more spiculation on the corpus bursae, though it would require a better dissection job than I managed to see this.

female Dark Meadow Grass-miner Elachista freyerella showing close-ups of head (2 angles) and genitalia, Sporle Wood (Norfolk, UK), 27th July 2023