Female horse fly head, coloured scanning electron micrograph (SEM). The head of the horse fly (family Tabanidae) is dominated by its large compound eyes. The sexes can be differentiated by the size of the eyes; males have larger eyes, which meet, while the eyes of females are separated by a space called the frons. Between the eyes are the horse fly's small antennae. This fly is a large fly that is considered a pest because of the painful bites many of the species inflict on humans and animals.