Large horse flies are gray or blackish. They use antennae to feel and smell. Flies' tongues are tube shaped and are used as a pump. The males drink nectar from flowers. When the females bite they suck the victims blood.
Females drink blood so they can get protein to develop their eggs.
They lay eggs on the front legs of horses, mules, or donkeys. When the eggs hatch they cling to the animals tongue when the animal licks its leg, then find their way to the stomach for nine to ten months. Then exit when the animal poops. Eggs can be laid with as many as 100 at a time. The eggs are long and spindle shaped.