Diagnosis. Similar to S. tormentillella and female S. stelviana; see these two species above. Male genitalia: see S. tormentillella. The female genitalia of S. dryadella, S. poterii, S. filipendulae and S. ulmariae probably not reliably separable; dryadella frequently has longer and stronger apophyses.
Male. Wingspan: 4.5-5.5 mm. Head: frontal tuft and vertex dark grey-brown to black; collar dark brown; scape shining pale golden; antenna three-quarters length of forewing, dark grey-brown. Thorax dark brown. Forewing: area proximal to fascia greenish golden to deep brownish golden, at base and before fascia dark copper brown; fascia at three-fifths, distinct, pale golden; distal to fascia dark copper brown with purple reflections; terminal cilia grey. Hindwing and cilia grey. Abdomen dark grey. Female. Wingspan: 4.5-5.5 mm. Male genitalia. Genitalia relatively large. Vinculum short; anterior margin with shallow emargination. Uncus short, with distinct, deep medial emargination and distinct paramedial notches. Valva broad; distal process short, pointed, directed inwards. Transtilla with straight transverse bar, forming obtuse angle to lateral arms; sublateral processes absent. Juxta absent. Aedeagus slightly longer than genital capsule; with one long, curved cornutus near tip having broad base and a proximal row of about 30 cornuti of different size. Female genitalia. Corpus bursae small, without pectinations. Vestibulum moderate, bilobed. Accessory sac about as large corpus bursae. Ductus spermathecae without spines. Apophyses short and strong. Ovipositor not protruding.
Host plant: Dryas octopetala. Egg: laid on edge or lower surface of leaf. Larva: yellow. Mine: follows the serrations along the margin of the leaf for about 10 mm and then abruptly widens into a blotch occupying about half the leaf. Cocoon: brown.
Not in Denmark. In northernmost Sweden from Lu.Lpm. and T.Lpm. In Norway only from Sti. Finland: Ks and Le. - Ireland, Scotland, Poland (Tatra), the Alps from France to Austria and N. Italy.
Voltinism: in Ireland and Scotland regarded as bivoltine (Emmet, 1976). In the Austrian Alps regarded as univoltine (Klimesch, 1981). There seem to be remarkable differences between different populations and altitudes. According to the original description (Hofmann, 1868), mining larvae collected at Oberaudorf, Bavaria, in mid-September pupated in the autumn. The moths emerged in the middle of June the following year. According to Wocke (1877 - N. Italy, Stelvio), Borkowski (1970 - Poland, Tatra), and Klimesch (1981 - Austria, Hinterstoder) all or the majority of the larvae hibernate in the mines and can be collected after the snow-melt, from March to late June depending on altitude. Moths have been collected all through the spring and summer, in N. Italy as late as October (EJvN). In northern Scandinavia and France all larvae leave the mines in the autumn. In N. Scandinavia larvae have been collected from mid-July to late August, moths from early July to late August. On sunny subalpine and alpine limestone slopes up to about 2400 m (Huemer, 1985). In Scandinavia from ca 350 to 700 m, but in Ireland along the coast (Burren).
Description based on Johansson and Nielsen (1990)