Description: Wingspan 50-64mm. Colour and appearance similar to the Lesser Swallow Prominent P. gnoma when at rest. The forewings are ochreous-white with a dark brown subapical patch at the costa. There is also a fine, white line along the marginal edge and a sub-dorsal streak from the basal area to the outer margin of the wing. The hindwing is yellowish white with a dark patch at the anal apex and has a small, white wavy line. The thorax and abdomen are dark brown. Generally from the beginning of May to early August, although some individuals can be found a little later in some years.

World Distribution: Throughout Europe as far east as Siberia.

Irish Distribution: Widespread over southern counties, but less commonly met with than the closely-related Lesser Swallow Prominent P. gnoma. The resemblance between these species could lead to some under recording, particularly where both species occupy the same habitat and with inexperienced recorders who are not totally familiar with the subtle differences between these species.

Ecology: An attractive moth found mainly in damp woodland, clearings and some bogs especially in north Armagh and Fermanagh. Adults appear commonly at light but always in small numbers. The larvae can be found from June until August on willows Salix spp. It overwinters as a pupa.

Key Identification Features:

• Resting posture
• No wedge-shaped mark on forewing
• Dark apical patch along the costa
• Small white wavy line on the anal patch of the hindwing

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

iNaturalist: Pheosia tremula at iNaturalist World Species Observations database.