Description: Wingspan 32-42 mm. Adults are sexually dimorphic. The males are usually lighter than females, but darker examples can also be found. Forewings are broad and vary in colour from reddish brown to dark brown. The costa is well-arched. The stigmata are not well-defined and the crosslines are often faint apart from the pale, wavy subterminal line. Hindwings greyish brown with darker veining. August to mid-September.

World Distribution: Local in Europe with a mainly northern distribution.

Irish Distribution: A scarce species, recorded recently from several sites in Down, Rostrevor Oakwood National Nature Reserve, Castlewellan Forest Park and Helen's Bay. Away from east Down, apparently rare. The only known sites are the Argory and Ardress House, Armagh and Correl Glen National Nature Reserve, Fermanagh.

Ecology: Mainly associated with acid woodlands, heaths and bogs. Adults are attracted to light in small numbers and also to flowers, such as Heather Calluna vulgaris and Ragwort Senecio jacobaea. The larvae feed from September until spring on birch Betula spp. and Bilberry Vaccinium myrtillus. It overwinters as a larva.

Key Identification Features:

• Broad forewings with a well-arched costa
• Greyish brown hindwings with darker veining

Distribution Map from NBN: Diarsia dahlii at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Diarsia dahlii at iNaturalist World Species Observations database.