[7] Rhagio mystaceus has an overall dark colour, with males growing to 7–9 mm, and females reaching 6–8 mm.

Normally, the center stripe has a very thin, pale line running down the middle.

On the abdomen, there are yellowish rings at the posterior of the segments.

However, the basal segment on some specimens are mostly yellowish and have a black dorsal and lateral spot.

[8] This article related to members of the fly superfamily Rhagionoidea is a stub.