White-line Dart Euxoa tritici
Wingspan 28-40 mm.
Inhabiting sand-hills and heathland, this species is distributed widely over most of the British Isles.
It can be difficult to tell apart from similar species, including Square-spot Dart (E.obelisca) and Coast Dart (E.cursoria).
It flies in July and August, and the larvae feed in spring on a variety of low plants.