Diagnosis. Extremely similar to occultella, for external differences see under that species. Male genitalia can be separated by smaller size, presence of large elongate cornuti and shape of gnathos. Female genitalia extremely difficult to separate, but minimella has usually shorter and wider signa, although there is some overlap.
Description. Male. Forewing length 2.32—2.72 mm (2.54 ± 0.11, 14), wingspan 5.1 — 6.1 mm. Head: frontal tuft black; collar black. Antennae with 35—42 segments (37.5 ± 2.2, 14). Thorax and forewings completely jet-black, less coarsely scaled than in other Ectoedemia species, with a rather broad, almost straight, dull white fascia, sometimes slightly constricted in middle. Hindwing with a greyish hair-pencil, slightly shorter than occultella. Underside of forewing without white scale patch. Female. Forewing length 2.28 — 3.04 mm (2.71 ± 0.24, 16), wingspan 5.1 — 6.6 mm. Head: frontal tuft black, or mixed with yellow and fuscous scales, sometimes completely yellow on frons, but always black on vertex; collar black. Antennae with 23 — 29 segments (26.3 ± 1.9,14). Male genitalia. Capsule length 296—321 µm (307.9 ± 11.6, 6). Tegumen produced into long tapering, pointed pseuduncus. Gnathos with narrow, truncate central element. Valva length 214 — 227 µm (221.0 ± 4.2, 7), outer margin strongly convex, inner margin slightly concave, almost straight; tip pointed, pointing posteriorly. Aedeagus 283—309 µm (237 ± 10.0, 6), carinae each divided into several blunt ending processes, number variable; vesica with about 20 — 22 long, needle shaped cornuti at right side, and many smaller cornuti in remaining part of vesica. Female genitalia. T7 without row of setae. T8 with two groups of scales and about 4 setae. Anal papillae confluent, with 23 — 32 setae in total. Vestibulum with vaginal sclerite, and dorsal spiculate pouch with very few minute spines only. Corpus bursae 440 — 550 µm, with pectinations in two lateral bands, at some distance from signa; signa dissimilar, longest 176 — 279 μm (240 ± 37.4, 7), shortest 167—231 µm (199.6 ± 24.9, 7), 2.0—2.4 x as long as wide. Ductus spermathecae with 2½— 3 convolutions. Larva. Pale yellow to yellowish white, with distinct brown ganglia. Head light brown. Penultimate instars with 12 black ventral plates.
Hostplants: Betula pubescens Ehrh., B. nana L., B. pendula Roth., Alnus viridis (Chaix) DC. in Lam. & DC. (Alps), Corylus avellana L. (British Isles). Mine. Egg deposited on leaf-underside. Early mine much contorted gallery, with dispersed frass, staining leaf brown; later abruptly enlarges into elongate blotch, which often fills the space between two veins; dispersed black frass.
Common and widespread in Scandinavia and locally in the Alps, but elsewhere very local and always less common than occultella. Estonia: Jürivete et al. 2000; Latvia: Savenkov 1989; Lithuania: Diškus 2003. See also Baldizzone 2004; Nieukerken et al. 2006 for records in France and Italy.
Life history. Univoltine. Larvae from July to October, adults fly from May to July.
This taxonomic description is based on Van Nieukerken (1985) and Van Nieukerken et al (2010).