By Dave Boxler
Face flies can carry pinkeye and eyeworms, and cause millions of dollars of economic damage every year.
One to five face flies per eye per day can cause serious ocular lesions that mimic the symptoms of bovine pinkeye. Mechanical damage, whether sustained by face fly mouth parts, dust, weed, pollen, or excessive sunlight, predisposes the eye for infection and increases epithelial discharges.
Infectious bovine keratoconjuntivitis (IBK), also known as pinkeye, is a common eye disease of cattle caused by bacteria; Moraxella bovis, M. bovoculi, and M. ovis, carried by face flies. Clinical signs of IBK are excessive tearing, eye inflammation, conjunctival edema, corneal opacity, and ulceration (Figure 1). Animals with IBK may exhibit weight loss, impaired vision, eye disfigurement, and blindness.
Face flies can also transmit Thelazia eyeworms which are nematodes that can infect several different host species and are found on nearly every continent. Clinical signs of infection resemble mild cases of pinkeye, including lacrimal secretions, conjunctivitis, corneal opacity, and lesions of the eye and surrounding tissues. Within the Unites States, the four Thelazia species eyeworms that occur in cattle and horses are exclusively transmitted by the face fly.
Horse and cattle behavior caused by face flies
Face flies are pests of pastured livestock animals such as beef cattle and horses. Livestock will react to fly feeding by bunching, seeking shade in trees or in some cases standing in water to avoid the flies. Fly feeding also prompts animals in pasture and rangeland to exhibit a variety of defensive behaviors, including head throws, tail flicks, and bunching together with their heads inwards to avoid attacking flies.
Face fly control for cattle
Control strategies for face flies include insecticide ear tags, dust bags, oilers/rubs, pour-ons, sprays, feed-throughs (also known as insect growth regulators or IGR-s), and air-projected capsules. Control methods that target the head area of an animal are the most effective. Non-chemical control methods include walk-through traps, sticky traps, and conservation of beneficial insects such as predatory dung-inhabiting beetles. Commercial and autogenous IBK vaccines are available to help manage IBK and if used, should be administered before animals are sent to summer pasture. Please consult with your veterinarian about the use of these vaccines.
Face fly anatomy and behavior
The face fly is a robust fly that resembles the house fly in appearance. Like the house fly, the face fly has a sponging type of mouth and feeds on animal secretions, nectar, and dung liquids. Only the female face fly will be found clustering around an animal’s eyes, mouth, and muzzle and causes extreme annoyance and irritation.
Females flies also feed on blood and other secretions around open wounds. Face flies are present throughout the summer, but populations usually peak in late July, August, and early September. They are more numerous along waterways, areas with abundant rainfall, canyon floors with trees and vegetation and on irrigated pastures. These widely distributed flies are native to Europe and Central Asia but are now found throughout North America north of 35ºN latitude.
Adult females use their sponging mouthparts with prestomal teeth that rasp, scrape, and penetrate the conjunctiva of host eye tissues, triggering tear production. Both sexes have sponging type mouthparts that absorb nectar and fluids from eyes, faces, and other body orifices.
Female face flies lay their eggs in fresh bovine dung pats. Larvae burrow into the moist dung and feed by filtering bacteria, yeast, and small organic particles from dung liquids. As the larvae complete their development, they leave the dung pat and burrow into the surrounding soil where they develop into the pupal stage. Males emerge 1-2 days before females. The complete life cycle can be completed usually in 18 to 20 days depending on temperatures. The number of face fly generations per year can range from 3 to 4 in northern latitudes to as many as 12 in the southern range. In late summer and early fall, as temperatures start to cool and day length falls below 12.5 hours, both sexes aggregate on sunny sides of natural and man-made structures. They will work their way into cracks and crevices where they eventually spend the winter, usually in areas such as attics, lofts, and walls of buildings, until temperatures are warm enough to draw them out in spring.
Annual losses in face fly control costs and lost animal production were estimated to exceed $52 million in 1967 for U. S. range cattle which would be approximately $469 million in 2023 dollars.Source : unl.edu