Both Anacampsis blattariella and A. populella are variable species with overlap in the forewing markings and colour, particularly in the extent of blackish markings. A transverse pale fascia at three-quarters (if visible) often has a strong zig-zag style in the costal half in A. blattariella (more curved in A. populella) but there is variation in this. Information received from some County Moth Recorders and other experienced moth recorders suggest those moths at the extremes (dull greyish fuscous or strongly black and white) are often identifiable from the forewing markings alone but the many intermediates and those which have become worn will not be identifiable without dissection, unless bred. Their comments are based on experience of the habitat and moths in their areas where both breeding and dissection have been carried allowing familiarity with the 'look' of their local moths to be applied. It is therefore suggested any caught specimens are retained for potential dissection (see more below).
Although adults found resting on the trunks of willows, poplars and aspen are likely to be A. populella, care should be taken as moths do wander and alder (an additional foodplant of A. blattariella) can be found where willow species occur.
The best way to become familiar with this pair at a site is to breed them through from known foodplants whilst also retaining a few trap-caught specimens for dissection. This will demonstrate if both species are present and develop familiarity with the range of markings present in your locality.
Examination of the photographs on this and other websites which specifically show dissected or bred specimens of both species is strongly recommended, as these illustrate some of the pitfalls in their identification. It is advisable to adopt a very cautious approach if attempting to either identify or use as a guide, specimens from websites or on-line postings where the specimens have not been critically examined or bred.
A. blattariella was first recorded in Britain in 1947 so documented records of non-bred A. populella prior to this period may well include records of A. blattariella.
To further complicate matters, it is mentioned in Emmet and Langmaid, 2002 The Moths of Great Britain and Ireland Vol. 4 (2), that although these two closely related species are considered to be clearly separated on the continent, the separation may not be so complete in Britain. 'Specimens reared by D A B Macnicol from larvae in rolled Betula leaves from Surrey in 1952 are large, weakly marked and have female genitalia approximating more to A. populella than to A. blattariella.'
