Fly Control That Works: What’s Worth Your Money This Summer

By Ann Asher

Every year about this time, it feels like the flies start winning. No matter how clean I keep the pens or how many fly strips I hang, they show up in clouds. Over the past few summers, I’ve tried just about everything—feed-through supplements, predator bugs, DIY traps, and plenty of fly sprays. Some things helped. Some were a waste of money. If you’re battling flies this year, here’s what’s actually worked for me—and what research says can make a real difference on the farm or ranch.

Start with Cleanliness (But Know It’s Not Enough)

The first—and most repeated—advice is to stay ahead of the mess. Manure management is critical, especially around barns, pens, and loafing sheds. Flies lay eggs in fresh manure, and those eggs hatch into larvae in as little as 24 hours during warm weather.
I try to clean high-traffic areas at least every other day, but the truth is, even on the cleanest farms, flies can still be a problem because of moisture, standing water, and nearby neighbors.

Feed-Through Fly Control: A Solid Foundation

One thing that made a noticeable difference for my horses and cattle was starting a feed-through larvicide early in the season. These products add a growth regulator to the feed that passes through the animal and prevents fly larvae from developing in manure.
It’s not an instant fix—you won’t see fewer flies for several weeks—but once it kicks in, you’ll notice fewer new flies being born.

Tip: Feed-through products only work if all animals on the property are eating it consistently. Otherwise, you’re just treating part of the manure, and flies will keep breeding.

Fly Predators: Small, Mighty, and Surprisingly Effective

Last year, I tried fly predators for the first time. These are tiny, non-stinging insects that lay their eggs in fly pupae, stopping the next generation.
I was skeptical (and honestly a little creeped out at first), but I noticed that where I used predators around the barn and dry lots, the fly pressure dropped. Some companies even offer subscription services that send predators timed to your local climate.

Tip: Fly predators don’t kill adult flies—they stop future flies. So you still need to control the adults already buzzing around.

Good Old-Fashioned Fly Traps

In areas like the barn aisle and outdoor runs, nothing beats physical traps.
I like a combination approach:

• Sticky ribbons and strips for indoor areas
• Odor-baited traps placed away from livestock areas to draw flies away

Tip: Hang baited traps a good distance from barns or stalls. Otherwise, you’re luring flies right into your animals’ space.

Fly Sprays: Choose Carefully

Fly sprays are the first thing most of us reach for—and they do help—but they have limits.
For horses, sprays containing pyrethrins, pyrethroids (like permethrin), or natural oils tend to offer the best repellency. Even then, most sprays only last a few hours, especially if animals are sweating heavily.

Tip: Apply before morning turnout and again before evening if possible. Reapplication is important, especially after heavy exercise or rain.

Other Tools That Help

• Fly masks and fly sheets — particularly those with UV protection, to protect sensitive areas like the eyes and ears
• Fans in barns and run-in sheds — flies struggle to land in strong airflow
• Automatic sprayer systems — an investment, but highly effective for larger barns

The bad news? There’s no magic bullet for fly control.
The good news? Combining several methods—manure management, feed-through treatments, predators, traps, and targeted sprays—can actually make summer bearable for you and your livestock.

At the end of the day, I figure if I can cut the fly population by half, I’ve already made life better for my animals—and a lot less miserable for myself.

References:

1. Texas A&M AgriLife Extension – Managing Flies on Livestock
2. University of Kentucky Entomology – Controlling Flies Around Livestock
3. North Carolina State Extension – Livestock Pest Management
4. USDA Agricultural Research Service – Fly Management Resources
5. Spalding Labs (for info on biological control programs) – Fly Predators Information