Diagnosis. S. floslactella is readily separated from all Stigmella species by yellowish colour without metallic lustre on the forewing. The only exception is the female of S. zelleriella; floslactella females have darker and coarser scales beyond the fascia than zelleriella. The male genitalia of floslactella have needlelike cornuti in the aedeagus, these are absent in S. tityrella; S. carpinella has larger and more numerous broad cornuti than floslactella; the distinctly dentate hind margin of the uncus in S. tityrella separates that species from both floslactella and carpinella. The female genitalia of floslactella and carpinella both have a band of modified pectination on corpus bursae; this band less distinct in floslactella than carpinella; the bursa of floslactella is markedly narrower than in carpinella.
Male. Wingspan: 5.0-6.0 mm. Head: frontal tuft, scape and collar yellowish white; antenna slightly longer than half length of forewing. Thorax concolorous with base of forewing. Forewing: area proximal to fascia ochreous, towards fascia and dorsum more or less densely irrorated with coarse brown scales (varying from a few brown scales at dorsum to entire basal half being brown); base of costa dark grey; fascia indistinct, pale ochreous; distal to fascia dark grey to blackish, coarsely scaled; terminal cilia strongly contrasting, pale ochreous. Hindwing: pale grey. Abdomen dark grey. Female. Wingspan: 5.0-6.0 mm. Antenna half as long as forewing. Forewing with more contrasting pattern than in male. Abdomen with pointed, protruding ovipositor and long, pale yellowish anal tufts. Male genitalia. Vinculum with broadly emarginate anterior margin. Uncus with hindmargin weakly dentate. Gnathos with very short transverse bar and long parallel horns. Aedeagus as long as genital capsule; with two clusters of cornuti: a proximal group of needlelike cornuti and a distal group of about 25 broad and short cornuti. Female genitalia. Corpus bursae long and narrow, completely covered with pectinations and with an indistinct band of modified pectinations. Accessory sac very small. Ductus spermathecae as long as corpus bursae. Apophyses very long; anteriores longer than posteriores.
Host plants: Corylus avellana, Carpinus betulus and Ostrya carpinifolia (in southern Europe). Egg: on the underside in the angles of the ribs. Mine from the beginning clearly visible (in contrast to S. microtheriella). Frassline in the first part thick, almost filling the mine, then more irregular, partly filling the mine in the last third and occupying about a third of its width. Larva: greenish white to yellowish white (in autumn leaves). Cocoon: pale yellowish.
Widely distributed in Denmark and Sweden up to Dlr. In southernmost Norway and Finland. - Widely distributed in Europe from Britain through central Europe to southern Europe.
Voltinism: bivoltine, larvae from the end of June to the end of July and September to beginning of October. Imago May-June and August.
Description based on Johansson and Nielsen (1990)