Davey, P., 2009: A thinly spread species in England and Wales, local in Scotland, the larva feeding on nettle (Urtica dioica) and hop (Humulus lupulus). In Dorset, the moth until fairly recently was rare and at low density in river valleys where hop festoons hedgerows, notably on the Stour, the Moors River, and the Piddle, but has increased quite dramatically of late. Originally there was little evidence to support a resident status for the species, but currently, the moth seems to be regularly recorded from a few sites, notably those close to river valleys. This increasing trend seems mostly due to immigration, with in excess of fifty moths trapped in 2001 and 2003 appearing amidst notable immigrations from mainland Europe. The national norm is for a single-brood in June and July, but the Dorset records indicate a double brood pattern, with the peak of the mid-summer brood one-third higher on average, than that of the early autumn peak. Coupled with this are the suspected immigrant peaks in late May, late July and early October, reflecting a trivoltine cycle abroad.
Given the capacity of this species to migrate, it is worth mentioning that two similar species occur abroad, so it may be worth checking dark 'Spectacles' examples, particularly at times of immigration. These two are similar to triplasia, although both are marginally greyer. Also, the inner-most semi-circular black line separating the ochreous region from the remaining dark ground colour of the forewing on triplasia, forms an acute angle (less than thirty degrees) as it approaches the basal edge of the forewing. The other two species have this line forming an angle of forty-five degrees or more with the basal edge of the forewing, so that it appears more of a shallow curve than a full semi-circle along its whole length. The two Continental species are: Abristola asclepiades which has a southern, central and eastern distribution in Europe including Iberia, Germany and southern Scandinavia, and Abristola agnorista which occurs in southern Europe and is essentially a Mediterranean species.
Recorded in 36 (90%) of 40 10k Squares.
First Recorded in 1932.
Last Recorded in 2019.
(Data up to end 2019)