Do horse flies bite humans?

Yes. Only the females bite, and they bite people as readily as horses. The bite is painful because they cut the skin instead of piercing it.

Why are horse flies so aggressive?

The females need a blood meal to make eggs, and they hunt by sight for large, dark, moving targets. On hot, still, sunny days they are at their most active, which is why they seem to come out of nowhere at midday.

Does fly spray stop horse flies?

Partly. Repellent sprays make a horse fly leave sooner, but they rarely stop every bite. For horse flies, physical cover such as a fly sheet and mask, traps and turnout timing do more than spray alone.

Will cleaning up manure get rid of horse flies?

No. Horse flies breed in wet soil near water, not in manure. Manure cleanup cuts stable flies and house flies, which are often the flies people mistake for horse flies.

What eats horse flies?

Birds such as swallows and purple martins, dragonflies, and some wasps catch them. Encouraging swallows to nest in the barn helps a little, but predators alone won't solve a horse fly problem.

How to Get Rid of Horse Flies: A Plan for the Barn, the Pasture and You

By Gayle Woods Editors Updated November 11, 2026 8 min read

Horse flies are the reason a quiet horse suddenly bolts across the pasture or kicks at its own belly. The bite hurts because the fly doesn't pierce the skin like a mosquito. It slices it open with blade-like mouthparts and laps up the blood. A horse that takes a few dozen of those a day loses grazing time and condition, and an itchy, sore horse is not a safe one to ride.

The usual advice is "use a good fly spray," and that is why so many barns stay buggy all summer. The flies that bother horses are several different insects that live different lives. A plan that works starts with knowing which ones you have.

Know which flies you are fighting

Watch where the flies land and when they show up. That tells you most of what you need.

Fly	Where it bites	Where it breeds	When it's worst
Horse fly and deer fly	Back, neck, belly, legs; big, painful bites	Wet soil, marsh edges, creek banks	Hot, sunny, still afternoons
Stable fly	Lower legs; looks like a house fly but bites	Wet manure mixed with bedding, spoiled hay around round bales	Warm mornings and late afternoons
House fly	Doesn't bite; clusters around eyes and wounds	Fresh manure and garbage	All day, all summer
Gnats and no-see-ums	Belly, mane, tail head, ears	Wet mud, slow water, damp organic matter	Dusk and dawn on calm days
Mosquito	Anywhere; bites are small	Standing water	Dusk to dawn
Bot fly	Doesn't bite; lays yellow eggs on leg hair	Inside the horse (larvae live in the stomach)	Late summer

Two things stand out in that table. Only the stable fly and house fly come from your manure pile, so cleanup alone won't help much against the others. And horse flies breed in wet ground that may sit on your neighbor's land, so you will never get rid of them entirely. With horse flies the goal is fewer bites, not fewer flies.

Horse flies: block them, trap them, and time your turnout

Female horse flies need a blood meal to make eggs. They hunt by sight, looking for something large, dark and moving, and they home in on warmth and the carbon dioxide in breath. The larvae spend months, sometimes more than a year, in mud near water, so nothing you spray on a horse touches the next generation.

What works, in order of how much it helps:

Physical cover. A fly sheet with a belly band covers the body where horse flies bite most, and a fly mask with ears protects the face. Light colors attract fewer horse flies than dark ones. Check our picks for fly sheets and fly masks.
Turnout timing. Horse flies fly in sun and heat and quiet down in shade, wind and darkness. On a heavy fly day, bring horses into a stall with a fan at midday and turn them out overnight.
Traps aimed at horse flies. The traps that catch horse flies use a dark ball or panel that warms in the sun under a cone. The fly circles the "animal," flies upward and ends up in a collection jar. Put traps in full sun along the path flies take from wet areas toward the horses, not in the barn aisle. See fly traps for horse barns.
Repellent on the horse. Sprays shorten how long a horse fly stays, but they rarely stop the bite completely. Use them to get through a ride or a short turnout, not as your only defense.

Shade helps more than many owners expect. A run-in shed or a line of trees gives horses a place where horse flies are far less active.

Stable flies and house flies: break the breeding cycle

These two are the flies you can actually reduce, because they breed where you work. In summer heat a house fly goes from egg to adult in about a week, and a stable fly in two to three weeks. If manure and wet bedding sit longer than that, you are raising flies.

Pick stalls and paddocks often. Manure that gets spread thin and dries out, or goes into a hot compost pile, kills the larvae. A pile that sits wet and untouched feeds them.
Clean up around round bales. The ring of trampled, wet hay and manure around a round bale feeder is one of the best stable fly nurseries there is. Rake it out or move the feeder.
Fix drainage. Leaky waterers and low spots that stay muddy give flies and gnats a place to lay eggs.
Use fly predators if your manure is under control. These tiny parasitic wasps lay their eggs inside fly pupae, which kills them. They don't sting people or horses. They work only on manure-breeding flies, and only if you release them regularly from spring onward.
Feed-through products pass into the manure and stop larvae from developing. They work on the same flies, in your horse's manure only, so a neighbor's untreated pile will still send flies over.

Fans in the barn help more than people expect. Stable flies, gnats and mosquitoes are weak fliers, and steady moving air keeps them off a horse standing in a stall. A stall fan rated for barn dust is worth the money in a buggy climate.

Gnats, mosquitoes and bot flies

Gnats and no-see-ums cause the itchy belly line and rubbed-out tail some horses get every summer. Horses that react badly have an allergy called insect bite hypersensitivity, often called sweet itch. These insects are tiny and feed at dusk and dawn in still air, so stall the horse with a fan at those hours. A fly sheet with a belly flap and a neck cover helps, and repellents work best rubbed into the mane, the tail head and along the midline of the belly.

Mosquitoes carry West Nile virus and the equine encephalitis viruses. Repellents help a little; vaccines matter far more, and your vet will treat these as core shots every year. Tip over anything that holds standing water, including old tires and buckets.

Bot flies don't bite but drive horses frantic as they dart at the legs to lay eggs. Scrape the small yellow eggs off the hair with a bot knife or grooming block every few days in late summer. Your fall deworming should include a dewormer that kills bot larvae.

Choosing and using fly spray

Most equine fly sprays are built on two kinds of ingredients:

Pyrethrins, from chrysanthemum flowers, kill flies fast but break down in sunlight within hours.
Pyrethroids such as permethrin and cypermethrin are synthetic relatives that last longer and are the main ingredient in most "long-lasting" sprays.

Many products also add a synergist that makes the active ingredient work better, and a sunscreen or oil base that helps it stick. Oil-based formulas last longer but attract dust. Water-based ones feel lighter and suit horses that sweat.

To get your money's worth:

Groom first. Spray on a dirty coat sits on the dust and not the hair.
Spray against the lie of the hair so it reaches the skin, and wipe it onto the face with a cloth instead of spraying near the eyes.
Reapply after a heavy sweat, a bath or rain. "Up to 14 days" claims are measured under ideal conditions.
Test a new product on a small patch first; some horses react to a particular formula.

Compare our fly spray picks by how long they last in real turnout, not by the number on the label.

Protecting yourself from horse flies

Horse flies bite people for the same reasons they bite horses: you are big, warm, moving and breathing out carbon dioxide. Ordinary insect repellents built for mosquitoes give only partial protection against them.

Wear permethrin-treated clothing. Permethrin is applied to clothes, not skin, and it kills or drives off flies that land. You can buy treated shirts or spray your own and let them dry before you wear them.
Choose light colors. Horse flies target dark, high-contrast shapes. A khaki or white shirt draws fewer than navy or black.
Cover up and add a hat. Most bites come on the head, neck and arms. Some trail riders stick a strip of blue sticky tape to the back of a cap; flies hit the highest moving point and get caught.
Use DEET or picaridin on exposed skin for whatever it adds, especially if mosquitoes are around too.
Ride early or late. The same midday heat that brings horse flies out is when you'd rather not ride anyway.

A horse fly bite on a person usually swells, itches and settles within a few days. Wash it, use a cold pack and an anti-itch cream, and don't scratch it open. See a doctor if it spreads, gets hot or you feel unwell.

A season-long checklist

Pest control works best when you start before the flies peak.

Early spring: fix drainage and muddy spots, start fly predators if you use them, check last year's sheets and masks for torn mesh.
Late spring: set traps out before the first hot week, start manure and bedding cleanup on a weekly rhythm, schedule mosquito-borne disease vaccines.
Summer: sheets and masks on daily, fans in the barn, midday stalling on heavy fly days, spray before rides.
Late summer: scrape bot eggs, keep an eye out for rubbed tails and belly scabs.
Fall: deworm for bots after the first hard frost, wash and store fly gear, empty and clean traps.

Sources

Frequently Asked Questions

: Yes. Only the females bite, and they bite people as readily as horses. The bite is painful because they cut the skin instead of piercing it.
: The females need a blood meal to make eggs, and they hunt by sight for large, dark, moving targets. On hot, still, sunny days they are at their most active, which is why they seem to come out of nowhere at midday.
: Partly. Repellent sprays make a horse fly leave sooner, but they rarely stop every bite. For horse flies, physical cover such as a fly sheet and mask, traps and turnout timing do more than spray alone.
: No. Horse flies breed in wet soil near water, not in manure. Manure cleanup cuts stable flies and house flies, which are often the flies people mistake for horse flies.
: Birds such as swallows and purple martins, dragonflies, and some wasps catch them. Encouraging swallows to nest in the barn helps a little, but predators alone won't solve a horse fly problem.