Description: Wingspan 32-40mm. Forewings heavily marked with dark wavy cross-lines. Outer margin pale brown with a scalloped fringe. Hindwings similar to the forewings but paler. From the end of June to early August.

World Distribution: Northern and central Europe, also north America.

Irish Distribution: Widely distributed but local, known from scattered sites mainly in southern counties. More frequently encountered in the fens and bogs of north Armagh than elsewhere including Brackagh Moss NNR, Selshion Moss and Annagarriff Wood NNR. In Down it has been taken at Lackan Bog and Belvoir Park. There are also recent records for Crom Estate, Garvary, Florencecourt and Reilly Wood NNR, Fermanagh.

Ecology: A rather scarce but distinctive moth, found in fens, damp woodland rides and clearings, particularly where willows are common. Adults appear sparingly at light and usually as single individuals. They become active at dusk and can be seen flying along woodland rides where they are easily netted. The larvae can be found from August to October on willow Salix spp. and Bilberry Vaccinium myrtillus. It overwinters as a pupa.

Key Identification Features:

• Many dark wavy cross-lines on all wings
• Scalloped fringe on wings
• Paler hindwings

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

iNaturalist: Rheumaptera undulata at iNaturalist World Species Observations database.