Diagnosis. S. viscerella is very similar to most other Stigmella species without fascia and spots, particularly the species of the sanguisorbae group. The genitalia of viscerella differ widely from those of all European Stigmella species. The male genitalia are characterised by the long inner lobe and the prominent curved process on the inner side of the valva. The female genitalia can be separated from those of all other unicolorous Stigmella species by the combination of long and narrow ductus bursae and vestibulum and large, oval corpus with dense cover of pectinations.
Male. Wingspan: 4.2-4.8 mm. Head: ochreous to fuscous; tuft on vertex often slightly paler; scape and collar whitish or yellowish white; antenna approximately half length of forewing. Thorax concolorous with base of forewing. Forewing: faintly shining bronzy brown, towards apex dark with faint purple tinge; terminal cilia brownish but silvery grey at tips. Hindwing: greyish brown. Abdomen fuscous.
Female. Wingspan: 4.8-4.9 mm. Antenna markedly shorter than half length of forewing. Otherwise similar to male. Male genitalia. Vinculum with broad and shallow to distinct emargination in anterior margin; corners short and subtriangular. Uncus with pair of distinct, triangular projections. Gnathos with prominent rectangular plate formed by transverse bar and anterior processes and with long outwardly-curved horns. Valvae widely separated from each other; with long and narrow inner lobe reaching almost to tip of distal process; innerside of valva with long and slender, hook-like process; setae on dorsal part of valva with minute lateral branches over almost entire length. Transtilla without distinct sublateral processes. Juxta broad and almost square, united with tip of aedeagus and inner surface of valvae by a membrane; juxta anteriorly articulates with ventral corners of valvae. Aedeagus about half as long as genital capsule; vesica with posterior hook, 25-35 small spines and at least 50 very small ones; cathrema very wide and prominent.
Female genitalia. Bursa copulatrix approximately fourfifths length of abdomen. Accessory sac small, rounded, with small, indistinct reticulate field at base. Corpus bursae oval, densely covered with pectinations. Ductus spermathecae narrow with few convolutions. Apophyses anteriores distinctly shorter than posteriores.
Host plants: Ulmus spp. Egg: on upperside. Larva: bright green. Mine : a gallery mine which starts with three or more half circles around the egg site followed by a rather short part, often following a rib, normally with at least one U-bend; mines on leaves exposed to sun are much shorter than those on shaded leaves; frass coiled, completely filling at least the first half of the mine. Cocoon: leather brown.
Not in Scandinavia and Finland. - Widely distributed in England and central, southern and southeast Europe. Extremely local in The Netherlands.
Voltinism: univoltine in northwest Europe, and bivoltine in southern Europe.
Description based on Johansson and Nielsen (1990)