The necessity for a fly control program for beef herds is inevitable and now is the time to plan your's for this year. The two major species of flies that cause the most serious decreases in beef production and require the most control efforts are the horn fly and face fly. The horn fly alone is estimated to cause animal losses to the U.S. beef industry of $700 million. Tests have shown that the annoyance, irritation and blood loss caused by flies can reduce weaning weights of calves nursing fly infested mother cows by 12 to 14 pounds; average daily gain of grazing yearly steers may be reduced 12 to 14 percent, or as much as 30 pounds during the grazing season. Both face flies and horn flies annoy cattle, resulting in reduced grazing time and increased energy expenditure.
The adult horn fly, which is about one-half the size of a house fly, has piercing/ sucking mouth parts and feeds on blood and tissue fluids of cattle. They spend most of their adult life on cattle and feed 20 to 40 times a day. They are normally found on the animal's back, but may migrate to the sides and the belly as the temperatures increase. They are weak fliers, but may be carried great distances by high winds. The females leave the animal to lay eggs only in fresh cow manure, where they hatch into larvae. The life cycle is completed in eight to 45 days depending on temperature and humidity. With the short life cycle they may complete a dozen or more generations during the warm months. The fact that adult horn flies spend most of their time on cattle makes their control much easier.
The face fly is about the size of a house fly. They are non-biting and feed on secretions from the eyes and muzzle. They avoid entering dark places, such as a barn, while on the animal. The female lays eggs on freshly deposited manure like the horn fly; however, unlike the horn fly they are present on cattle only about 10 percent of the time and may be found resting on fence posts, trees, bushes and other objects the other 90 percent of the time. Because they spend so little time on the animal and do not feed on blood they are much harder to control than horn flies. When feeding around the eyes, they cause irritation creating an environment suited to bacterial growth. As the eye becomes irritated and begins to weep, it attracts more and more flies, adding to the irritation and opportunity for spread of infection. In addition to being an annoyance to the animal they are thought to be spreaders of bacterial organisms that cause pinkeye.