Entomologists call them Musca Autumnalis; farmers and ranch workers call them face flies. In any case, they are a major disease-spreading pest of livestock. Face flies are the single-most common cause of pinkeye in cattle and goats in the Ozarks region.
Bovine pinkeye has been particularly prevalent in the summer of 2010, according to Eldon Cole, a livestock specialist with the University of Missouri Extension. New strains of the conjunctivitis bacteria, as well as face fly populations, are likely to blame.
“They live in a world of their own, you might say,” Cole remarked in reference to face flies. He said that controlling them is a different and sometimes more challenging effort than controlling horn flies and other biting fly species. Face flies do not have bloodsucking mouth parts, and cannot bite. They instead lick or suck moisture from around the animal’s eyes and nose. They are closely related to house flies, and are about the same size.
Dr. Sally Burd, a Manes, Mo., veterinarian, said that face fly reproduction can be kept under control by “breaking up the manure so it’s exposed to the weather,” during the fall and winter months. Face flies lay their eggs in fresh manure, and the larvae (maggots) need to be completely surrounded and protected in animal waste in order to develop. The same is true of horn flies. By harrowing the pasture or using a raking implement, the manure masses or “cowpies” can be reduced to crumbles, greatly reducing the number of surviving face flies and horn flies the following spring.
Some farmers use oral larvicide products, such as the Vigilante bolus, to control the flies’ reproduction. The bolus, administered orally to the animal in May or early June, is intended to give season-long protection against face fly and horn fly reproduction. The bolus contains a chemical which passes into the animal’s feces, preventing the fly larvae from living there. Oral larvicides, however, are not to be used on cows that are actively being milked, since the larvicide chemical may enter the milk. Moreover, Dr. Burd warns that these products may be ineffective if being used only by a single farm, “because face flies can fly,” she noted. She said that it would be effective, more likely, if a group of neighbors were all using oral larvicides.
Eldon Cole agrees with this assessment. “Face flies can fly a couple hundred yards at least,” he said, citing entomologists who found that the flies can still reproduce if there is a significant amount of manure within that distance, such as from an untreated neighboring herd. He also noted the wide-ranging habits of face flies, stating that they do not live entirely on livestock, but spend a lot of time on fence posts and on grass,” among other places. He said that the best control methods for face flies are regular or continual ones, rather than one-time-a-year treatments such as the bolus.
Other such treatments include ear tag strips and rub-offs. Ear tag strips are hung on the animal’s ears while rub-offs are hung in places where the herd must pass daily, such as at the entrance to the milking barn or at a gate. Rub-offs are hung low where they will brush off on the face, or are hung on the sides of the passageway, where they will brush off on each animal as it passes through. For face fly control, the hanging type are preferred.
Rub-offs and ear tag strips are typically treated with pyrethrates, derived from the pyrethrum plant, although a few brands use synthetic pyrethrate, made from petroleum derivatives. Traps are another form of fly control, although they work more effectively against biting flies, (horn, stable, horse, and deer flies) than they do against face flies.
In fly control, most experts agree that the most effective approach is to use multiple methods. This also provides a more thorough strategy against the multiple species of flies that attempt to bite livestock, most commonly the horn fly. Horn flies also lay eggs in fresh manure, and according to Mr. Cole they are “probably one of the easier flies to control.” Although they are not as apt to spread disease as face flies are, horn flies can suck a liter of blood from one cow or bull each day.
