Description: Wingspan 28-38 mm. Adults show considerable variation in shade and colour. Forewings range from reddish brown through to light ochreous brown. The median area tends to be darker than the ground colour giving the impression of a band. There is also a small dark discal spot present on all colour forms. Stigmata are not usually conspicuous in any colour form. Antemedian line is fine and runs obliquely towards the costa. The postmedian line curves in towards the costa. The colour of the lines varies with the ground colour of the forewings but all are clearly defined. Hindwings range from fuscous through to whitish ochreous with a small discal spot which is not always evident. Mid-July to early September.

World Distribution: Widespread throughout western Europe as far north as Fennoscandia.

Irish Distribution: Widespread across southern counties and commonly encountered in many well-trapped sites. Sporadic further north, but it has been recorded from Rathlin Island.

Ecology: A summer species found in damp woodland and a variety of other habitats. Adults rest by day on ground foliage; they come frequently to light and occasionally visit the flowers of Ragwort Senecio jacobaea. The larvae feed from April to early June on oak Quercus spp., birch Betula spp., elm Ulmus spp., Hazel Corylus avellana, Hawthorn Crataegus monogyna and willow Salixspp. The larvae also feed on other caterpillars. It overwinters as an egg.

Key Identification Features:

• Oblique antemedian line
• Small dark discal spot on forewing

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

iNaturalist: Cosmia trapezina at iNaturalist World Species Observations database.