It’s the time of year when a maddening — and potentially menacing — pest takes hold in many a barn across the nation. University of Minnesota Associate Professor Brad Heins, who oversees the studies at the West Central Research and Outreach Center, tackled the topic of fly management in a recent “Moos Room” podcast, noting that the various types of flies attracted to dairy cattle create issues that can affect cow behavior, welfare, and ultimately production. And while sometimes producers lump all fly species into one bucket, declaring simply that “the flies are out,” Heins explained that different livestock behaviors and problems can be traced to specific types of flies, and identifying the exact species will help with management efforts. He broke down the most common culprits into their preferred domains — confinement and pasture.

Confinement flies are typically found in barns and reproduce in organic debris such as manure and bedding. Types include:

Stable flies. Heins said this species is of concern because stable flies are blood feeders and bite livestock. Each fly will feed one to two times a day, he explained, and will lay 500 to 1,000 eggs in spilled feed, manure, or bedding. The eggs take about a month to develop into adults, with a life span of approximately two to four weeks. Stable flies most often bite cows’ legs, which can result in bunching, tail switching, and foot stomping. A good way to identify stable flies is to check if the flies are on the cows right-side up, Heins advised; they don’t typically feed upside down. He also said, “Stable flies don’t really stay on the cows — they rest overnight in vegetation or on structural surfaces, so you might not see them on the cows all the time.” An untreated stable fly problem could lead to heat stress, reduced intake, and milk losses; estimates put those losses at about $2 billion nationwide.

Houseflies. While houseflies do not bite cattle — they feed on secretions from the eyes, nose, and mouth, as well as manure and plant sugars — they can be a nuisance, irritating cows around their faces, wounds, and teats. They’re typically found in decaying organic matter and lay fewer eggs than stable flies do.

Pasture flies — which, true to their name are not typically found in the barn — also can present problems for dairy cattle, said Heins. Pasture fly species that might have staked their claim on your pastures or lots include:

Horn flies. These reproduce in manure, and just like stable flies, they are blood feeders with sharp piercing mouths that penetrate animal hide. However, Heins stressed that horn flies feed much more often than stable flies — up to 40 times a day. They also reproduce much faster. He said to look for them on the back and sides of cows, as well as on their bellies — the last is a favorite shady spot during the hotter parts of the day. “Horn flies are about half the size of a housefly, with flat wings. They feed facing downward, so that’s a good telltale sign,” he added. Again, a swarm of these pests can lead to cattle bunching and its attendant heat stress, as well as drops in feeding, growth, and production.

Face flies. Heins said these are not blood feeders; like the housefly, they are attracted to bodily secretions and wounds. “Typically, you’ll only find them on the face and head,” he noted. “Even if you only have around 10 face flies per animal, it really decreases their feeding time.” And face flies are not just cause for irritation, they are cause for concern: they are effective disease carriers, especially when it comes to pinkeye.

Heins stressed that flies can travel for surprisingly long distances: up to 10 miles for horn flies; 12 miles in the case of the stable fly; 4 miles for face flies; and 2 miles for the housefly. These long-range stats go a long way toward explaining how a squeaky-clean operation can suffer from an infestation. Still, sanitation is the first line of defense when taking the fight to the flies, Heins advised. Manure management, cleanup of feed and bedding spills, especially rotting materials, will limit breeding ground. Other tips and techniques he offered were:

• Eliminate standing water and keep bedding dry.
• Release fly predators such as parasitic wasps.
• Use high-speed fans to disrupt flight.
• Pasture rotation can help spread out manure and reduce buildup of flies in one area.
• Put out fly traps and baits, including sticky and ultraviolet traps.
• Use sprays or insecticides — though he reminded listeners that can these products require reapplication and good sanitation.

Heins mentioned that emerging techniques to control horn fly issues include a vaccine, which is currently being tested at the University of Minnesota Extension Morris Farm. “It could be a long-term sustainable solution to reducing fly populations,” he said. “Is it going to create zero flies on our farm? Absolutely not, but I think it could be a good tool.”

Ultimately, Heins said there is not yet a silver bullet for fly control, but a thoughtful approach and proactive planning can keep cows more comfortable and minimize production loss.

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