70.052 Xanthorhoe ferrugata (Dark-barred Twin-spot Carpet) 1725
fw: 12-13mm; bivoltine in S.England May-Jun, Jul-Aug, univoltine further north May-Jul; various herbaceous plants; common throughout GB
ID: This species and X.spadicearia (Red Twin-spot Carpet) can be very similar. According to Waring the crucial distinguishing feature is a notch in the proximal margin of the dark central band close to the costa; however it seems that this is unreliable (Ref: Difficult species guide). X.ferrugata is dimorphic. The nominate red-banded form is less common than the black-banded form unidentaria. Specimens with a black band lacking any red-purple colour can safely be identified as X.ferrugata f.unidentaria. The difficult species guide referred to above states that 'well-marked X.spadicearia are quite distinctive', referencing Townsend 2010, however it does not provide us with any of the features that are supposed to be distinctive. It seems that X.spadicearia can have quite a lot of blackish in its median band. For now, I will assume that any example with any red in its median band will require genital dissection to distinguish between this pair of species. X.quadrifasciata (Large Twin-spot Carpet) is larger (fw 14-16mm) and has a more prominent elongate dark central forewing spot.
Page published 05/04/2013 (§1-5) | §6 added 09/12/2013 | §7 added 02/05/2014