Although adult face flies are nonbiting creatures, their feeding habits make them troubling to cattle. Face flies feed on the secretions produced by the eyes and noses of large animals. Beyond irritating cattle, this behavior also can result in the transmission of diseases. Affected animals often hide in dark places, produce less milk and lose weight. Face flies may also inflict pinkeye upon the animal and can transmit eye worms to both cattle and horses.
Face fly eggs are yellow, white or translucent in color. Each egg measures approximately 3 mm in length and 1/2 mm wide. Two ridges are located along their sides. When face flies enter the larval stage, they resemble yellow maggots. Adult face flies measure 6 to 8 mm in length and appear similar to house flies. Both males and females have gray thoraxes with four dark-brown stripes.
Female face flies lay their eggs only in the manure of grass-fed cattle. They prefer manure that is less than one hour old and avoid other feces. Eggs hatch within manure, and larvae develop under a crust of the manure. Upon maturity, face fly larvae crawl into soil close to the manure in order to complete the pupal stage. After a week or so, adult flies emerge above the soil. Complete life cycle of face flies requires approximately two weeks.