Fenusa pusilla (Lepeletier) - Adult(s) The Birch leafminer. a native to Europe and well established in N.E. United States, is a small sawfly that feeds on the tissue between the upper and lower surfaces of birch leaves. The host plant may show no symptoms of decline for several years, however, repeated leaf loss year after year, could be fatal to the tree.
The small, white and slightly flattened larvae of the birch leafminer live within the birch leaves. They can be easily seen when the leaves are held up to the light. The adult is a black fly-like insect about 3/16" inch long.