The face fly, Musca autumnalis, is a robust fly that superficially resembles the house fly. It is a nonbiting fly that feeds on animal secretions, nectar, and dung liquids. Adult female face flies typically cluster around the animals' eyes, nose, and muzzle, causing extreme annoyance. Their activity around the animals' eyes allows face flies to serve as vectors of eye diseases and parasites such as pinkeye and Thelazia eyeworms. They are also "facultative blood feeders," which means that they gather around wounds caused by mechanical damage or biting fly activity to feed on blood and other exudates.
By contrast, male face flies feed only on nectar and dung. They spend much of their time resting on branches and fences and attempting to catch and copulate with female flies as they move about. Females lay their eggs on very fresh cattle droppings on pasture, and development from egg to adult is completed in about 2 to 3 weeks, depending on temperature.
Face flies are strong fliers that can travel several miles. Unlike house flies, face flies do not enter darkened barns or stables during the summer months. In the fall, however, they enter buildings and overwinter indoors in a state of diapause, or hibernation.
