Every summer, producers ask the same question: What should we spray?
By the time adult flies are covering cattle, however, the next generation is often already developing somewhere else on the farm. According to Dr. David Prentice, veterinarian and technical consultant with Elanco Animal Health, successful fly control starts long before producers reach for an insecticide.
“Fly populations are like icebergs,” he says. “The flies that we’re actually seeing are only about 20%. Then we’ve got the army behind them. That would be the pupae, the larvae and the eggs. We need to consider everything below the surface.”
That “below the surface” mindset changes how we should approach fly management. Rather than focusing solely on adult populations, herd visits become an opportunity to identify the environmental conditions allowing flies to reproduce in the first place. Different fly species also exploit different areas of the farm, making identification just as important as selecting a control strategy.
Stable flies are among the most important arthropod pests of cattle because their painful bites reduce feed intake, weight gain, feed efficiency and milk production, particularly during heavy infestations. Understanding where those flies develop is often the first step toward reducing their impact.
Behind the Feed Bunk
Feed alleys often attract attention because cattle spend so much time there, but more valuable clues may be found by looking just behind the bunk. Small accumulations of feed that escape routine scraping can create ideal breeding sites for stable flies, particularly when moisture and organic material begin to decompose.
“A lot of times TMR will get stuck in there, and that is an ideal place for rotting TMR. TMR is loaded with goodies for stable flies,” Prentice explains.
Prentice recommends routinely inspecting these overlooked areas. Feed that falls behind bunks during push-ups can accumulate over time, and even relatively small pockets of decaying organic matter can support fly development. A shovel and a few minutes of cleanup each week may eliminate one of the farm’s most productive breeding sites before adult populations begin to climb.
Around Calf Housing
Calf housing presents another hotspot that deserves closer attention. While bedding inside hutches is routinely managed, the perimeter often receives less scrutiny. Moisture from urine, rainfall and organic bedding materials creates an environment where stable flies can thrive.
“On the perimeter of that calf hutch where the urine comes and it rains, this is going to be stable fly heaven,” Prentice says.
Between calves, these areas can often be cleaned or refreshed. During occupancy, however, they may be more difficult to access, making routine observation especially important. The edge of the hutch may reveal more about future fly pressure than the bedding inside.
Feeding Areas in Beef Systems
For grazing cattle, feeding rings create similar challenges. Hay waste, manure and moisture accumulate in one location, producing ideal conditions for fly development.
“These feeding rings are notorious because you get hay around them,” Prentice begins. “With moisture and manure that is the absolute perfect environment for stable fly reproduction.”
The lesson extends beyond hay rings. Anywhere decaying organic material mixes with moisture can become a productive fly nursery. Feed refusals, bedding piles and neglected corners around feeding areas all deserve attention during a farm walk.
Different Flies, Different Farms
One reason fly control programs sometimes fall short is that not every fly behaves the same way. Identifying the species involved should guide where you look and what management recommendations to make.
Horn flies, for example, rely on fresh manure pats to complete their life cycle, making them far more common in pasture systems than on confinement dairies where manure is disturbed or removed more frequently.
“Horn flies only lay eggs in fresh manure,” explains Prentice. “That’s why this is not typically a dairy fly as opposed to a pasture fly.”
Face flies also depend on fresh, undisturbed manure, while stable flies are more commonly associated with moist organic matter such as feed refusals, bedding and hay waste. Knowing which fly is causing the problem can prevent producers from targeting the wrong areas of the farm.
Look Beyond the Cow
One of the biggest misconceptions in fly control is assuming flies spend most of their time on cattle.
“What you see is not what you get because they don’t spend all of their time on the animal. They actually spend very little time on the animal,” explains Prentice.
Stable flies leave cattle after feeding to rest in shaded vegetation, tall grass and protected areas around buildings before returning for another blood meal. That behavior helps explain why treating cattle alone often produces disappointing results. During herd visits, veterinarians should evaluate the entire environment, not just the animals, when investigating persistent fly problems.
Ultimately, Prentice says successful fly management begins with sanitation rather than chemistry.
“Step one really is to clean up your environment. Step two is to concentrate on that 80%, the larval side, so that the adult fly population doesn’t grow to too high of a peak,” he advises.
The next time producers ask what they should spray, veterinarians may be able to provide a more valuable answer by asking a different question first: Where is the next generation of flies developing? Finding those hidden hotspots can shift fly control from reacting to adult populations toward preventing them in the first place.
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