Horse flies are in the family Tabanidae in the insect order Diptera and date back thousands of years. Photo by Chelsey Marques on Unsplash a horse with a blinder on it's headWhy Do Horse Flies Bite People and Horses? Why Do Horse Flies Attack Your Car? According to MaggiesFarmProducts.com, female horse flies detect humans and animals by colors and movements. Unfortunately, horse flies can be tough to deal with because they are persistent and their bites hurt.