Black-margined Fen Fly

For terminology see Speight key to genera and glossary Length, 3.3–5 mm (0.13–0.20 in). The head has blackish antennae, with the third joint being red on the lower part and brownish on the upper border. The front of the head is finely roughened, while the face appears whitish with a pollinose texture. In males, the eyes touch each other, a condition known as holoptic The thorax is lightly roughened with a metallic greenish bronze color, which gives it a moderate shine. The abdomen is lightly punctate and moderately shining. It is predominantly black, although the third segment may have two small spots. The abdomen appears slightly narrowed at the posterior of segment one and the anterior of segment two. Segment two is twice as long as it is wide. The wings are nearly transparent, with a dilute yellow stigma. The vein M joins the vein R4+5 at approximately a right angle. The crossvein r-m is located at the basal quarter of the discal cell. The posterior angle of the discal cell is almost a right angle. The legs have the black femora, except for the base and tip are yellowish. The hind tibiae are black with yellow base and tips. The front and mid-tarsi are yellow, while the first and last two joints of the hind tarsi are black.