Diagnosis. The combination of dark head, narrow and uniformly coloured forewings and absence of androconial scales in male hindwings separates it from S. anomalella and all other Rosaceae-feeding species. In the male genitalia the shape of the uncus and the two apical groups of long cornuti in the aedeagus distinguish spinosissimae from those of other Rosa feeders. Female genitalia characterised by the pointed abdominal tip, small bursa copulatrix, very small accessory sac and very fine and long pectinations.
Male. Wingspan: 4.0-4.6 mm. Head: frontal tuft fuscous; collar and scape dull white; antenna about half length of forewing. Forewing: narrow, unicolorous, shining pale bronze with grey and copper reflections; terminal cilia concolorous. Hindwing: grey, with faint bronzy reflections. Abdomen: fuscous. Female. Wingspan: 4.0-4.6 mm. Similar to male.
Male genitalia. Vinculum with distinct concavity and rounded lateral corners. Uncus distinctly bilobed, with U-shaped emargination in posterior margin; lateral margins of lobes strongly sclerotized. Gnathos with short horizontal element and long horns. Valva with pointed, arcuate distal process and rounded inner lobe, constricted at base. Transtilla with lateral arms and horziontal bar forming an U-shaped band without sublateral processes. Aedeagus slightly shorter than genital capsule; with two apical groups of numerous, long and slender, weakly sclerotized cornuti and with a patch of very small spines in posterior half.
Female genitalia. Bursa copulatrix about half length of abdomen. Corpus bursae with very fine and long pectinations. Accessory sac very small; reticulate field small and indistinct. Ductus spermathecae three-quarters length of bursa copulatrix, posterior part narrower and with one or two convolutions. Abdominal tip pointed. Apophyses posteriores short and sharply pointed; anteriores distinctly longer, pointed.
Host plants: Rosa pimpinellifolia (= R. spinosissima). Egg: usually on underside near mid-rib. Larva: bright amber yellow; head dark brown. Mine : a long gallery, starting very slender then gradually widening; it closely follows every serration of the leaf and then often doubles back; in small leaves occupying almost the entire leaf; frass in broad central line leaving clear margins. Cocoon: yellowish brown; on leaf or at base of leaf-stalk.
Only known from a few localities in Ireland and Britain (see Emmet, 1976).
Voltinism: bivoltine; larvae in July and September.
Description based on Johansson and Nielsen (1990)