The yellow-tail, goldtail moth or swan moth (Euproctis similis) is a moth of the family Erebidae. It is distributed throughout Europe to the Urals, then east across the Palearctic to Siberia. It is also found in Sri Lanka.
This species has a wingspan of 35–45 mm, the female usually noticeably larger than the male. All parts of the adults are pure white, apart from a bright yellow tip to the abdomen (larger in the female) and a small black or brown tornal mark on the forewing of the male.
Technical description and variation
White, and very like Euproctis chrysorrhoea, but more pure silky white, anal wool and hairs at the apex of the abdomen of the female golden yellow. Not rarely, especially in the male sex, varieties occur with small dark spots on the forewing: auriflua [Esper, 1785] has three spots at the inner angle, forming an oblique transverse row, and one spot in the basal area near the hindmargin; nyctea Gr.-Grsh. has only one spot at the inner angle as well as one in the basal area like auriflua; trimaculata ab. nov. [Strand] is like nyctea. but has another spot on the costal margin opposite the subbasal inner marginal spot, while quadrimaculata ab. nov. [Strand] has a fourth subapical spot. The two last-named forms are from eastern Asia, where spotted specimens of this species seem on the whole to be commoner than in Europe 
It flies at night in July and August  and is attracted to light, especially the males.
Larva black, with sparse black grey hairs, a brick-red divided longitudinal dorsal stripe, white lateral stripes and black head, segment 1 black streaked with yellow, the tubercles on segments 4 and 11 also black. It usually feeds on trees and shrubs such as alder, apple, birch, blackcurrant, blackthorn, cherry, chestnut, hawthorn, oak, rowan and sallow. It has also been recorded on monkshood, which is a herbaceous plant. This species overwinters as a larva. The larvae disperse soon after emerging from the eggs, which are covered with the anal wool of the female, hibernate singly and pupate at the beginning of June. Pupa blackish brown in a whitish cocoon. It is common everywhere in the distribution area, but not in such numbers as the very similar Euproctis chrysorrhoea, and not noxious. The moth comes to the light and when at rest folds the wings very steeply in roof-shape; when touched it feigns death, lying on its side with the wings closed.
- Yellowtail moth – a moth from South America
- Kimber, Ian. "Yellow-tail Euproctis similis". UKMoths. Retrieved 19 November 2016.
- Colour Atlas of Siberian Lepidoptera
- Fonseka, Avijja. "Yellow tail moth caterpillar from Talangama wetlands, Sri Lanka". flickr.com. Retrieved 15 June 2016.
- Strand, E. in Seitz, A. Ed. Die Großschmetterlinge der Erde, Verlag Alfred Kernen, Stuttgart Band 2: Abt. 1, Die Großschmetterlinge des palaearktischen Faunengebietes, Die palaearktischen Spinner und Schwärmer, 1912- 1913
- Chinery, Michael Collins Guide to the Insects of Britain and Western Europe 1986 (Reprinted 1991)
- Skinner, Bernard Colour Identification Guide to Moths of the British Isles 1984
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