How to Repel Horse Flies – Proven Methods That Work

From May to September, every UK and South African horse owner fights the same battle: how to repel horse flies before they bite. Unlike the lazy stable fly that lands and walks, the horse fly slices the skin with bayonet-like mouthparts and leaves a wound that can bleed for hours. Beyond the obvious pain, repeated bites trigger insect-bite hypersensitivity (sweet itch) flare-ups, allergic dermatitis, weight loss from constant stamping, and open wounds that can develop into summer sores. In rare cases they transmit equine infectious anaemia, a notifiable disease in the UK and South Africa.

The good news: a layered approach actually works. This guide covers the chemistry of UK fly sprays, fly rugs and masks that earn their keep, the Bristol University zebra-stripe research that’s reshaped fly-rug design, biological and yard-management options, and the homemade vinegar mix that NAF and Carr & Day & Martin owners genuinely fall back on when their bottle runs out.

Know Your Enemy: UK Horse Fly Species

The UK has around thirty horse fly species in the family Tabanidae, but three account for the bulk of bites on horses and humans:

• Cleg fly (Haematopota pluvialis) — the most common British biter, a smaller, drabber fly that lands silently. Often the one that gets you on a hack before you spot it
• Twin-lobed deerfly (Chrysops relictus) — bright green eyes, prefers shaded woodland, viciously persistent
• Common horse fly (Tabanus bromius) — the bigger, classic horse fly that announces itself with an audible drone

All three are at their worst from late May into September, particularly on humid, still days near water, woodland, or cattle. Females do all the biting — they need a blood meal to develop eggs. Males live on nectar and never bother horses or people.

Why Horse Flies Bite (And What Attracts Them)

Knowing what draws horse flies in tells you what to neutralise. Tabanids are guided by:

• Carbon dioxide — they detect breathing animals from up to 50 metres away
• Heat and large dark shapes — bay and dark grey horses are bitten more than light greys
• Movement — a swishing tail and head shake actually attract more flies
• Sweat and ammonia — well-worked or poorly-mucked horses smell like a target
• Polarised light off water — horses standing in shallow streams or near still water are sitting ducks

You can’t change a horse’s body heat, but you can change its silhouette, smell and skin coverage — which is exactly what a layered repellent strategy does.

Fly Sprays and Repellents That Actually Work

Active Ingredients to Look For

Application Tips

• Apply to a clean, dry coat — sweat and dust block contact with the skin
• Never spray a horse’s face — decant into a sponge or cloth and wipe carefully around eyes and nostrils
• Pay particular attention to the belly, sheath, dock, ears and the line of the jugular groove — favourite Tabanid targets
• Reapply after rain or sweating; oil-based sprays last longer than water-based
• Patch-test on the inside of the elbow first — even natural sprays cause reactions in sensitive horses

NAF Off Citronella, Carr & Day & Martin Flygard, Lincoln Insect Repellent and Switch are the four most reached-for UK yard sprays. The strongest summer ammunition is generally a permethrin-based product like NAF Off Deet Power applied with discipline.

Fly Rugs, Masks and the Zebra-Stripe Effect

Why Coverage Beats Spray on Bad Days

A well-fitted fly sheet solves what a spray can’t: physical blocking. The best UK rugs cover from poll strap to dock, with belly flaps and detachable necks. Look for tight-weave Ripstop mesh that bites can’t push through, and an under-belly closure rather than a single chest strap, since horse flies target the belly heavily.

The Zebra-Stripe Research

In 2019, researchers at the University of Bristol (published in PLOS ONE) tested why zebras have stripes by dressing horses in striped, plain and chequered coats. Striped and chequered coats had dramatically fewer landings — the moving black-and-white pattern appears to disorient Tabanids’ visual approach. Major UK brands (Bucas, Premier Equine, Horseware Amigo, Shires Tempest) now offer zebra-print and chequered fly rugs based on this research, and anecdotally most yards that have switched report fewer bites on rugged horses.

Fly Masks and Ear Nets

The face is where horses can’t dislodge flies. A fly mask with an ear net makes the biggest welfare difference of any single piece of fly kit. Flies clustering at the eyes are a major cause of equine conjunctivitis, so face cover is as much about eye health as comfort. Choose UV-blocking mesh for sensitive eyes, and check fit weekly — a mask that’s rubbed bald patches into the cheekbones is no help to anyone.

Yard and Stable Management

Cutting the breeding population is slower than spraying but ultimately more effective.

• Muck out daily — Tabanid larvae develop in damp, organic-rich mud, but stable flies and bots breed straight in manure. A clean yard knocks out the supporting cast
• Move muck heaps — at least 30 metres downwind from the field and stable
• Drain standing water — old tyres, blocked gutters, abandoned drinkers, soggy gateways are all nurseries
• Cut long grass in the field margins where flies rest in the heat of the day
• Use stable fans — Tabanids cannot fly into a stiff air current, and fans cool the horse at the same time
• Hang sticky paper in the stable and aisles for adult catches

Fly Traps That Catch Tabanids

Most domestic fly traps catch houseflies and stable flies but ignore Tabanids. Two specialist designs target horse flies specifically:

• H-trap (Horse Pal-style) — a black ball under a transparent cone collector. The ball heats in the sun and looks (and smells, to a fly) like a large dark animal. Flies investigate, hit the cone, and trap themselves. Works best in open, sunny positions away from buildings
• NZI trap — a fabric trap originally developed for tsetse fly research; uses dark blue and black panels and CO₂ lures. Available in the UK from larger horse-fly specialist suppliers

One H-trap can catch hundreds of horse flies a season in a problem field. They cost £150–£300, but compared to the value of a comfortable, bite-free summer they pay for themselves in a year.

DIY and Natural Remedies

The KBIS / Yard Vinegar Spray

The recipe most often shared on UK yards mixes:

• 500 ml apple cider vinegar
• 500 ml water
• 2 tbsp vegetable oil (helps it cling to the coat)
• 20–30 drops citronella essential oil
• 10 drops eucalyptus or tea tree oil
• Optional: a tablespoon of washing-up liquid as an emulsifier

Decant into a labelled sprayer. It’s not as long-lasting as a permethrin product, but it smells better, costs almost nothing, and is genuinely effective on the days the flies are merely annoying rather than apocalyptic.

Plants Around the Yard

Pots of basil, lavender, rosemary, lemon balm and citronella geranium near tack rooms, stable doors and aisles add a constant low-level deterrent and look pleasant. Don’t expect them to single-handedly clear a field, but they’re a meaningful addition.

Garlic and Apple Cider Vinegar in Feed

Adding garlic granules or apple cider vinegar to the daily feed is a long-standing yard tradition. Evidence for either is patchy, but neither will harm a healthy horse fed at sensible rates. Avoid garlic for horses with anaemia or those scheduled for surgery, and always discuss feed additives with your vet first.

Biological and Feed-Through Control

• Fly predators (Spalding-style) — micro-wasps that parasitise pupating flies. They don’t sting, don’t target horses, and cut adult fly numbers by 30–80% in studies. Released weekly into muck heaps and damp areas. More effective against stable and houseflies than Tabanids, but reducing the supporting fly population still helps
• Feed-through larvicides (e.g. Equimins Garlic Plus or specialist insect-growth regulators) — pass through the gut and prevent fly larvae from developing in manure. Useful in heavy-stocking yards
• Chickens and ducks — every yard with fowl in the muck heap notices fewer flies. Ducks in particular eat fly larvae enthusiastically

Turnout Timing and Daily Routine

Tabanids are at their most active between 10 am and 6 pm on hot, still, humid days. The cheapest fly-control measure on the planet is reverse turnout: out at night, in during the day, when the bite pressure is highest. Most UK livery yards in summer adopt this rhythm by July.

• Bring horses in for the worst hours and run a stable fan
• Hose off sweat at the end of work — sweat is a fly magnet
• Check the belly, ears, sheath and udder daily for fresh bite welts; if the skin is broken, see our guide on how to treat a horsefly bite. Untreated bites are a common entry point for the skin infections that plague horses in summer
• Watch for sweet-itch type reactions on the mane and tail in midge-sensitive horses

Protecting Yourself from Horse Fly Bites

Riders, grooms and yard owners are bitten as often as the horses are. The same chemistry works on humans:

• DEET-based or PMD-based human repellents (Jungle Formula, Mosi-guard) on exposed skin
• Long sleeves and trousers in pale colours — Tabanids strongly prefer dark targets
• Avoid floral perfumes and dark synthetic fabrics in the field
• If bitten, clean the wound with soap and water; antihistamine cream eases the itch
• See a doctor if redness spreads more than a few centimetres or a bite shows signs of cellulitis — Tabanid bites infect more readily than midge bites

A Layered Approach: What to Stack

No single tactic on its own clears the air. The combination most yards land on is:

1. A well-fitted zebra-stripe or fine-mesh fly rug with belly flap
2. A fly mask with ear covers
3. A permethrin or DEET fly spray on exposed coat (legs, neck, dock)
4. One H-trap per problem field
5. Reverse turnout in peak Tabanid hours
6. Tight muck management and standing-water control
7. A stable fan for the hottest indoor periods

Done together, this stack typically reduces bites by 80–90%. Done piecemeal, you’ll spend the summer chasing the same swelling on the same belly.

Frequently Asked Questions