The 'daggers' get their English names from the black dagger-like markings on the forewings.
This moth is almost impossible to tell by the markings alone from the Dark Dagger (
), and reference usually has to be made to the genitalia for confirmation. The caterpillars of the two species are quite different, however.
It flies between June and August and is common throughout England, Wales and Ireland, scarcer in Scotland.
The colourful larva is marked with red and yellow and has a tall 'hump' on the back, close to the head.