Diagnosis. The long black androconial scales on the male hindwings are distinctive. Females can be recognized by the combination of almost white head, relatively narrow forewings with constricted, silvery fascia and pale grey cilia, sharply contrasting with dark distal part of forewings. Both male and female genitalia differ widely from all other Stigmella species. The mines of S. tityrella and hemargyrella are somewhat similar but in tityrella the egg is always laid on the underside in the angle of the ribs; the mine winds between two ribs, rarely crossing ribs, and the larva has clearly visible ganglia and dark head capsule.
Male. Wingspan: 5.5-6.5 mm. Head: frontal tuft white to pale ochreous; collar lead grey; scape yellowish white; antenna half length of forewing, pale grey. Forewing: narrow, area proximal to fascia shining brown, frequently with more or less prominent olive green lustre, shading into purplish brown at fascia; fascia slightly oblique, silver to pale golden, usually constricted in middle; distal to fascia dark brown to purplish fuscous, terminal cilia pale grey, contrasting with distal part of wing. Hindwing: brownish grey with slightly paler cilia; at base of costa a conspicuous pencil of long black androconial scales. Abdomen: dark grey with yellowish grey anal tufts. Female. Wingspan: 5.2-6.3 mm. Antenna slightly less than half length of forewing. Hindwing grey, without androconial scales. Abdomen grey, tip blunt. Otherwise similar to male.
Male genitalia. Vinculum wide, with wide almost uniformly concave anterior emargination. Uncus with long, widely separated latero-posterior processes and truncate medial hump. Tegumen semicircular, at least as wide as uncus. Gnathos with heavy anterior processes and thin, weak horizontal bar; horns normally parallel but position variable depending on the weak medial part. Valva triangular with short, pointed
distal process and very small rounded inner lobe. Transtilla with long heavily sclerotized transverse bar and long, pointed sublateral processes. Aedeagus longer than genital capsule with large and wide manica and 5-6 short processes at tip. Vesica with numerous, mainly triangular cornuti of varying sizes, the largest near tip of aedeagus. Female genitalia. Corpus bursae egg-shaped, densely covered with long and prominent pectinations; both sides of bursa with heavier pectinations in slightly sunken bands. Ductus bursae long, curved and well sclerotized with many transverse folds. Accessory sac absent. Ductus spermathecae thin, without spines. Apophyses widely separated and equally long. Abdominal tip blunt.
Host plant: Fagus sylvatica. Egg: usually on upperside, away from midrib. Larva: pale greenish yellow with pale brown head capsule; ganglia not visible. Mine : a long winding gallery frequently crossing ribs. The first half of the mine almost completely filled with coiled, dark brown frass; in the second half more irregularly dispersed, leaving clear margins. Cocoon: pale yellow.
Denmark: reported from almost all provinces; south- western Sweden to Dls. in north. Reported from Norway but no material has been available. Absent from Finland. - Central Europe to Poland and Hungary in the east, northern and southern Italy, the British Isles. Closely following the distribution of Fagus sylvatica but also found on planted trees outside the native range of Fagus.
Voltinism: bivoltine; mining larvae from the middle of June to the end of July, and September to early october. Adults can easily be collected on beech trunks from the beginning of May until the middle of June; the adults of the less common summer generation fly from mid-July to early August.
Description based on Johansson and Nielsen (1990)