deer fly

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.
• noun A gold or green eyed horsefly of the genus Chrysops in the family Tabanidae; pests to cattle, horses and humans, feeding on their blood.