Horse Flies: What Actually Works

Some of the best answers to this one aren't things we sell. Here they are anyway.

Every summer, somebody stands at our counter holding a bottle of fly spray and asks why it isn't working on the big ones. It's a fair question, and the honest answer is that the big ones are a different insect that needs a different approach — and a few parts of that approach we don't carry, don't profit from, and will happily point you toward anyway.

We do sell some of what's below — boots, masks, sheets, and sprays — and we'll say so when we get there. The traps we don't sell, don't stock, and earn nothing from. Those links are here because they're the right answer for some of you.

The short version

If you only have two minutes:

• Horse flies are not stable flies or house flies. They breed in wet mud, not manure, so a lot of the fly-control aisle is aimed at a different bug.
• Physical barriers work best. Fly sheets, masks, and especially leg protection.
• Zebra stripes have real research behind them — not a novelty pattern.
• Fly spray does work on these flies, but only with genuinely full-body coverage and daily reapplication. Partial coverage is why most people think it fails.
• Large visual traps help, but each one covers roughly two acres — far less than the marketing suggests.
• Turnout timing may be your cheapest fix. These flies hunt in sun and avoid shade.

First: know what you're fighting

This is the step almost everyone skips, and it's the one that determines whether anything else you do works.

Horse flies and deer flies (family Tabanidae) are large, fast, and visually driven. Their big eyes pick out movement and shapes that contrast against the background — which is why dark-colored horses draw more flies than light-colored ones in the same pasture. Only the females bite. Their mouthparts cut the skin to create a pool of blood they feed from, which is why the bite is so much worse than a mosquito's.

They carry disease, too. Horse and deer flies mechanically transmit equine infectious anemia — the virus your Coggins test looks for — by carrying it on their mouthparts from an infected horse to an uninfected one. They've also been implicated in transmitting tularemia, which affects people as well as animals.

Females lay eggs on vegetation next to wet habitat — marshes, streams, ponds — and the larvae develop in the mud there. Not manure. Not your bedding pile.

Stable flies, house flies, and face flies (family Muscidae) are the smaller ones, they do breed in manure and soiled bedding, and they're the target of most of the traps, baits, and biological controls on the market.

Confuse the two and you'll spend a season treating your manure pile for a fly that never went near it.

What actually works

1. Physical barriers

Unglamorous and effective. Mesh keeps mouthparts off skin, and there's no resistance, no reapplication, no wearing off in the heat.

• Leg and belly coverage deserves particular attention. These flies will bite anywhere on the body, but legs and belly are where they return first as other protection wears off — and they're exactly what a standard sheet leaves open. This isn't only about comfort: excessive stomping can lead to hoof damage and potential lameness. We stock several options, including [Fly Free Fly Boots], and we wrote a longer piece on [choosing fly boots] if you want to go deeper.
• Masks protect eyes and ears. [We carry several], including a locally made one — we'd rather stock a neighbor's work than a warehouse's.
• Fly sheets cover the body. Availability is seasonal, so check the site or call the store.
• Check daily for rubs and heat, especially on thin-skinned or clipped horses.

2. Zebra striping

This one sounds like a gimmick and isn't.

A 2019 study in PLOS ONE by Caro and colleagues filmed horse flies approaching zebras and solid-colored horses. Flies circled both at similar rates — but landed on the zebras less than a quarter as often. In a follow-up, the same horses wore black, white, and striped coats in sequence; the striped coat drew far fewer touches and landings. The flies approached too fast and failed to decelerate, so they bounced off or overshot instead of settling.

One honest caveat from that same study: there was no difference in attack rates on the horses' bare heads. Stripes protect what they cover. A striped sheet is not a striped mask.

Read it yourself (open access): https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210831

3. Fly spray — if you actually cover the horse

Here's the part most people get wrong. Full-body application of synthetic pyrethroid repellents does work on horse and deer flies. The problem is that these flies will bite any part of the body, so partial coverage leaves open targets — and as the product wears off, they come back to the legs and belly first.

• Cover everything. A quick spritz over the topline is not treatment.
• Use a brush or microfiber mitt. Apply the product to the mitt, then to the horse. You'll get far better coverage than spraying alone, and it's quieter for horses that dislike the hiss.
• Reapply daily at minimum, and again before riding in areas where these flies are active.
• Sweat-resistant and oil-based formulas hold up longer in heat and humidity.

If spray has "never worked" on horse flies for you, coverage and frequency are the first things to examine.

4. Large visual traps

These exploit the same instinct that makes a dark horse a target — a big dark object in the sun reads as an animal. The fly commits, and the trap's geometry does the rest.

Four types exist. Three are practical for a horse property:

• Horse Pal — a suspended black ball on a four-legged frame under a canopy. Flies strike the ball, follow their instinct to fly upward, and funnel into a clear collection jar. No bait, no power. Now made by Capralite. https://capralite.com/products/horse-pal-complete-fly-trap
• Bite-Lite H-Trap — same ball-and-canopy principle on a single post. https://www.bite-lite.com/
• Epps Biting Fly Trap — a large dark panel flanked by clear plastic deflectors. Circling flies hit the invisible panels and drop into soapy water trays. Needs four 7-foot T-posts, sold separately. Trays need frequent cleaning, or new arrivals climb out on the bodies of the old ones. https://www.arbico-organics.com/product/epps-biting-fly-trap/pest-control-horse-livestock
• Box traps are another type, mostly used in salt marsh settings. Probably not your situation in Missouri.

All of these run into the mid-hundreds before shipping, and prices move. Check the manufacturer links for current numbers.

Which one? Honestly: nobody can tell you. The best head-to-head is Kline, Hogsette and Rutz, Journal of Vector Ecology (2018), which compared traps at two Florida sites and one in North Carolina — and found that the winner changed depending on the location.

• At Lower Suwannee Wildlife Refuge, the H-Trap led with 2,006 specimens, ahead of the Nzi (938) and Horse Pal (541).
• At Cedar Ridge Ranch, the Nzi won decisively with 1,439, against 215 for the H-Trap and 161 for the Horse Pal.
• In North Carolina, the H-Trap caught about twice the Horse Pal, 1,458 to 720.

The authors' own conclusion is that trap type mattered at every site, but not the same trap type. If you see a manufacturer citing this study as proof their trap is best, they're quoting the site where they won.

The Nzi trap in that comparison is a fourth design — a cloth flight-interception trap developed for tsetse and tabanid surveillance. It's less common on horse properties but clearly capable.

Set your expectations on coverage. Penn State Extension estimates a properly placed trap covers about two acres. You'll see one manufacturer claim "reduces biting flies 80%, covers 20 acres, rated #1 by Cornell." We couldn't trace that Cornell attribution to anything, and the acreage figure is ten times what the extension literature supports. The user reviews are genuinely enthusiastic. The numbers are sales copy.

Placement matters more than brand:

• Put traps where the flies are a problem — small pastures, near arenas, anywhere horses can't escape the bites.
• Sunny spots, visible from the woods or marshy ground the flies come from, away from buildings that block their line of sight.
• Horses must not be able to reach or interfere with the trap.
• Never use insecticide on or near the trap. It repels the flies you're trying to attract.
• Expect trial and error. If a trap isn't catching, moving it a few yards can change the results substantially.
  

Penn State Extension has the best neutral overview: https://extension.psu.edu/protecting-horses-from-horse-and-deer-fly-bites

5. Timing, shade, and which pasture

Free, and underused. These flies are daytime hunters that want sun, and they avoid shade.

• Night turnout, or midday in
• Run-in sheds and canopy trees — sited away from wooded edges — give horses somewhere to self-manage
• Some species are territorial, holding to one pasture or even part of one. Moving horses to a different field sometimes solves the problem outright
• More pasture space lets horses walk away from fly pressure on their own

6. Drainage

If the wet ground producing them is on your property, fixing it does more than any product on this list. If it's the neighbor's marsh or the creek bottom, it isn't fixable, and traps and barriers become your plan. Worth knowing which situation you're in before you spend anything.

What underperforms, and why

• Fly predators. Excellent products used correctly. They parasitize the pupae of manure-breeding flies. Horse fly larvae develop in wet mud away from the barn, where predators never go. Keep using them for stable flies; don't expect help with horse flies.
• Jug traps, scatter baits, and sticky ribbons. Designed for flies with different behavior — bait traps rely on odor, and sticky ribbons rely on flies resting on surfaces. Horse and deer flies do neither. Penn State names these specifically as ineffective for tabanids.
• Feed-through garlic. No credible evidence against tabanids, and enough reason for caution that we don't recommend it. A University of Guelph study found horses fed garlic above 0.2 g/kg daily developed Heinz body anemia, and that horses will voluntarily eat that much; recovery took about five weeks after stopping. Be fair to the evidence, though: that study used four horses, only two of them fed garlic. A later trial at lower doses found no Heinz body effect. The National Academy of Sciences places the threshold where risk rises meaningfully somewhere between 15 and 200 mg/kg, depending on the individual horse. Nobody has established a safe long-term dose — which is the actual problem.
• Ultrasonic devices. We could not find any published evidence that these work on biting flies. If a manufacturer has a study, we'd genuinely like to see it.

"What about Deep Woods Off?"

We get this one enough that it deserves a real answer, and the real answer has two halves that point in opposite directions.

The chemistry works better than you'd expect. DEET has been tested against these exact flies:

• A 2016 Swiss field trial applied a 15–17% DEET emulsion to horses and counted tabanids three and four hours later. Untreated horses carried as many as 29 flies. Treated horses peaked at four, and half of them had none at all. The authors reported efficacy of at least 80% at three hours and 71% at four — those are conservative floors, not the average result.
• A 2025 randomized trial in Gabon tested repellents against deer flies on people. DEET cut biting attempts roughly in half. Two other common repellents, icaridin and IR3535, did nothing measurable.

So DEET isn't snake oil. It has real tabanid data behind it.

The can in your tack trunk is a different story:

• Concentration. The Swiss study used a 15–17% oil-water emulsion built for horses. Deep Woods Off is 25% DEET in a base made for human skin — and the Sportsmen line runs 30%, 40%, and higher.
• Skin damage is documented. In older equine work cited by that same study, repeated dermal application of DEET at 15% or higher produced hypersteatosis in horses, and horses sprayed at 75% showed exfoliation across several body regions. Daily whole-body application at 25% is asking for a skin problem.
• It isn't labeled for horses. No equine dosing guidance, no toxicology data at horse surface area. A person covers a couple of square feet. A horse is a different exposure question, and nobody has answered it.
• DEET is a plasticizer. According to the National Pesticide Information Center, it can damage rubber, plastic, vinyl, and elastic — eyeglass frames and lenses, watch crystals, painted and varnished surfaces, and certain synthetic or treated fabrics. It does not harm cotton or wool. Overspray in a tack room is expensive.
• Cost. Covering a horse with aerosol Off is absurd per ounce next to an equine spray.

Where it makes complete sense: on you. Deer flies hunt people as readily as horses, and Deep Woods Off is doing exactly what it was formulated and labeled to do on human skin. Spray yourself. Just keep it off the horse and away from your tack.

Before you use any repellent on a horse you plan to show, check with your association — rules vary and they change.

Where this leaves you

For most riders and most horses, the answer is barriers plus timing plus properly applied spray. Leg protection, a mask, thorough daily coverage, and a turnout schedule that avoids the worst hours will get you most of the way there.

Traps are a property-level decision — worth it for a boarding barn, a show grounds, or anyone whose pasture backs up to standing water. If that's you, put your money in placement and patience, not the brand name. And plan on more than one if you've got acreage.

And if you want to talk it through, come see us. We'll tell you when the answer isn't something on our shelf.

Every rider. Every horse. Every journey.

Sources

We'd rather show our work than ask you to take our word for it.

General horse and deer fly management — biology, disease transmission, trapping, turnout, and repellent application Machtinger E. "Protecting Horses From Horse and Deer Fly Bites." Penn State Extension, updated 2022. https://extension.psu.edu/protecting-horses-from-horse-and-deer-fly-bites

Zebra striping Caro T, Argueta Y, Briolat ES, et al. "Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses." PLOS ONE 14(2): e0210831, 2019. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210831

Trap comparison Kline DL, Hogsette JA, Rutz DA. "A Comparison of the Nzi, Horse Pal® and Bite-Lite® H-Traps and Selected Baits for the Collection of Adult Tabanidae in Florida and North Carolina." Journal of Vector Ecology 43(1): 63–70, 2018. Free full text: https://onlinelibrary.wiley.com/doi/full/10.1111/jvec.12284

DEET on horses Herholz C, Kopp C, Wenger M, et al. "Efficacy of the repellent DEET against tabanid flies on horses evaluated in a field test in Switzerland." Veterinary Parasitology, 2016. Free PDF: https://www.bfh.ch/dam/jcr:f9b97fc0-0d76-4a22-9bdc-ba3cd9035555/Herholz%20et%20al.,%202016%20VETPAR_Repell.pdf The older equine skin-reaction findings we cite (Blume et al. 1971; Palmer 1969) appear in this paper's literature review.

DEET and deer flies on people Placebo-controlled randomized trial of DEET, icaridin, citriodiol, and IR3535 against Chrysops bites, Gabon, 2025. https://www.sciencedirect.com/science/article/pii/S147789392500105X

DEET and materials National Pesticide Information Center, Oregon State University. DEET Technical Fact Sheet. https://npic.orst.edu/factsheets/archive/DEETtech.html

Garlic Pearson W, et al. "Association of maximum voluntary dietary intake of freeze-dried garlic with Heinz body anemia in horses." American Journal of Veterinary Research 66(3), 2005. https://avmajournals.avma.org/view/journals/ajvr/66/3/ajvr.2005.66.457.xml

Trap manufacturers (we don't sell these and earn nothing from these links) Horse Pal / Capralite: https://capralite.com/products/horse-pal-complete-fly-trap Bite-Lite H-Trap: https://www.bite-lite.com/ Epps Biting Fly Trap: https://www.arbico-organics.com/product/epps-biting-fly-trap/pest-control-horse-livestock