The adult black deer fly, Chrysops niger, is a fly of about 8–10.5 millimetres (0.31–0.41 in) length, with a mostly black body with some white hairs, and having wings which are barred with black. They are active from May to September around areas of marsh in much of the United States. The larvae of the black deer fly feed upon organic matter in damp soil, and are termed hydrobionts in that they inhabit areas of high water content.