Deer Fly, a large fly that attacks deer and, less frequently, such livestock as cattle and horses. Female deer flies are bloodsuckers and can transmit tularemia (rabbit fever), anthrax, and other diseases. The males feed on pollen and nectar. Deer flies have stout bodies and broad heads with bulging, bright green or gold eyes. The adults are about one inch (2.5 cm) long and are black with yellow-green markings and brownish-black, patterned wings. The females lay masses of shiny black eggs on stems or leaves of plants growing in marshes, streams, and ponds. The newly hatched larvae, which are white, drop into the water below. Eventually, the larvae, which feed on snails and insects, swim to the mud or peat at the edge of the water, where they pupate. The adults emerge from May through August.
Deer flies make up the genus Chrysops of the family Tabanidae.Deer flies have stout bodies and broad heads with bulging, bright green or gold eyes.