A close up of a deer fly.
The definition of a deer fly is a fly that sucks blood from mammals like deer. It is smaller than a horse fly. The common name for this insect is often spelled "deerfly." However, according to the Entomological Society of America (ESA) the correct common name of this insect is "deer fly."
An example of a deer fly is is a fly with a dark band on the wings that infest deer.
(plural deer flies)
- A Eurasian species of louse fly in the family Hippoboscidae, Lipoptena cervi; parasites of elk, deer and other bovine animals, sucking blood and laying eggs in the fur of the host animals.
- A gold or green eyed horsefly of the genus Chrysops in the family Tabanidae; pests to cattle, horses and humans, feeding on their blood.