Wing length is 13 to 16 mm and 16 to 22 mm in body length. A fairly large horse-fly. The dark abdomen has a central row of pale triangles and a dark and broad central stripe on the underside. The eyes lack stripes.
Its habitat is normally wet grassland and marshy areas, especially when cattle are present. Often seen sunning on fences, not hovering.
Tabanus autumnalis, the large marsh horsefly, is a medium-sized species of biting horse-fly. It is somewhat scarce compared to T. bromius and T. bovinus. This species shows slightly more of a preference for coastal marsh than some of the other European Tabanus, sometime even found in saltmashes. Wing length is 13–16 mm and about 16–22 mm in body length.