Head brown with a mixture of white hairs; forewing ground colour brown; whitish pattern consisting of some inconspicuous costal and dorsal striae. In some specimens, the forewing could be described as white ground colour with brownish pattern. In both cases, there are two dark brown patches at the dorsal margin, just before and just after the centre.

Yellowish green when young, later instars have the thoracic segments and the first abdominal segment yellowish without any markings; abdominal segments 2–8 somewhat darker yellow and with a distinct dark brown to blackish central patch in the middle of the dorsum. Sometimes the 9th abdominal segment also has such patch. Head light brown.

A rather large, tentiform mine on the underside of a leaf, with one conspicuous, central, longitudinal fold. The mine occupes one side of the leaf, never crossing the main vein. On the upperside the mine is visible as a light green patch, later on, when the caterpillar consumes the parenchyma, the mine becomes transparant whitish, with sometimes a remaining central green patch. The frass is concentrated in a corner of the mine.
See also gracillariidae.net and bladmineerders.be.

Pupation in the larval feeding place in a flimsy cocoon far from the corner where the frass is concentrated. Pupa dark brown. The species hibernates in the pupal stage. After emergence of the adult, the pupal skin protrudes from the mine.

The larva mines narrow-leaved willows with a preference for Salix alba and S. babylonica, much more rarely on S. fragilis. It also has been recorded occasionally on Populus.