these two moths from last week show quite well the differences between the uppersides of these two species; the colour of the main crossband isn't always the best feature to go on, as dark-barred twin-spots in particular are quite variable, sometimes fairly red, as in this one. where i trap in the ystwyth valley, these reddish forms are quite common. i've labelled the dark-barred twin-spot carpet photo to show some of the distinguishing (and otherwise) features. for the dark-barred twin-spot, the main crossband (1) is broader, the twin-spots (2) are isolated rather than part of a band or partial band, the marginal area (3) is chalky white rather than darker, the narrow off-white crossband (4) is even narrower and the general colour (for example at 5) is less vivid. the crossband immediately outside the main crossband (6) is often described as less pure white in the dark-barred twin-spot but these particular specimens suggest that this might sometimes be a bit too subtle to be reliable. the undersides are also distinctive, the dark-barred twin-spot being more drab, the red twin-spot more orangey. the notch in the front edge of the dark-barred twin-spot's main cross-band (7) was formerly used to distinguish this species, until it was noticed that red twin-spots also sometimes have it.