Diagnosis. Adult tityrella can be separated from all other Stigmella species by the white, oblique fascia, the slender abdomen, the spots on the underside of the forewings of the male and the scale tufts on the hindwing costa of the males.
Male. Wingspan: 5.0-6.0 mm. Head: frontal tuft pale yellow; collar yellowish white; scape white; antenna reaching three-fifths of forewing, pale grey at base, darker grey distally. Thorax olive grey. Forewing: area proximal to fascia olive grey, purplish brown towards fascia; fascia oblique, white; distal to fascia purplish brown; terminal cilia pale grey; near base of underside of forewing a patch of dark brown scales. Hindwing: grey, basal part pale brown along costa; cilia grey; base of costa on underside with a brush of pale hair-like scales. Abdomen dark grey, slender. Female. Wingspan: 5.0-6.0 mm. Antenna reaching approximately to middle of forewing. Hindwing uniformly pale grey on both sides. Abdomen with protruding ovipositor and long yellowish white anal tufts. Male genitalia. Vinculum with anterior margin broadly emarginate; lateral corners pointed. Uncus small, hind margin distinctly dentate. Gnathos with short horizontal bar, horns long and slender. Aedeagus as long as genital capsule; with 10-20 small triangular cornuti near tip and about 20 larger triangular cornuti. Female genitalia. Corpus bursae small and slender, with sparse, hardly visible pectinations. Accessory sac large. Ductus spermathecae at least as long as corpus bursae. Apophyses very long and slender.
Host plant: Fagus sylvatica. Egg: always on the underside among the hairs in the angles of the midrib. Larva: pale greenish yellow with dark brown head. Cocoon: yellowish. Mine : meandering in the space between two sideribs. Frass line blackish, occupying about two-thirds of the width of the mine.
From all districts in Denmark; in Sweden up to Vstm; in Norway only from VE. Not in Finland. - Widely distributed in central Europe including Britain.
Voltinism: bivoltine. Larvae in July and September-October. Adults from the second half of May to the middle of June (2-3 weeks later than S. hemargyrella) and in August.
Description based on Johansson and Nielsen (1990)