Do Horse Flies Bite? Discover the Truth About These Pesky Insects

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Horse flies and deer flies are a common nuisance for both humans and animals, particularly during the warmer months. These insects are known for their persistent and painful bites, which can affect animals like horses, cattle, and deer as well as people.

Female horse flies and deer flies are the ones responsible for inflicting these bites, as they require a blood meal for egg development. They may target any area of the body, but deer flies typically bite around the head and neck, while horse flies often go for the legs source. Though horse flies and deer flies are notorious for bothering horses, they have a wide host range, attacking various mammals and even sometimes birds and reptiles source.

It’s crucial to protect yourself and your animals from these painful bites, not only for comfort but also because they can transmit diseases. Taking preventative measures can make a world of difference. Horse and deer flies can be deterred, for instance, with proper use of repellent source.

Understanding Horse Flies

Physical Appearance

Horse flies are moderate to large-sized flies, measuring around 14 to 19 mm in length. They have a grayish-brown thorax and clear wings. These flies also have distinctive large eyes that can be brightly colored. Deer flies, on the other hand, are smaller ranging from 10 to 13 mm in length, with greenish-yellow thoraxes, dark-striped patterns, and smoky gray-brown tinted wings source.

Habitat and Distribution

Horse flies are primarily found in North America, where they thrive in damp, marshy areas or near bodies of water. They prefer warm and humid environments. This is why you’ll often find them around pastures or wooded edges, as well as other damp or lush areas source.

Tabanidae Family

Horse flies and deer flies belong to the Tabanidae family of insects. These bloodsucking flies are known for being a nuisance to humans, cattle, and horses. While some species of horse flies may feed on humans in Indiana, deer flies are more likely to do so. They feed on a wide range of hosts, including mammals, birds, and reptiles source.

Key Differences Between Horse Flies and Deer Flies:

Feature Horse Flies Deer Flies
Size 14 to 19 mm 10 to 13 mm
Color Grayish-brown thorax Greenish-yellow thorax
Wings Clear Smoky gray-brown tinted
Feeding Behavior Some species may feed on humans More likely to feed on humans

Some Traits They Share:

  • Both are bloodsucking insects.
  • Can be a nuisance to humans and animals.
  • Belong to the Tabanidae family of insects.

Horse Fly Bites

How They Bite

Horse flies have sharp mouthparts designed for cutting through flesh, allowing them to extract blood from their host. Female deer flies especially are known to feed on various mammals, with some species even targeting reptiles and humans. They usually bite on the host’s head and shoulders while it moves.

Pain and Symptoms

When a horse fly bites, it can cause significant pain and discomfort. Common symptoms following a bite include:

  • Intense pain due to sharp mouthparts
  • Swelling and inflammation around the bite area
  • Redness surrounding the wound
  • A potential rash

Some individuals may also experience more severe reactions to horse fly bites, such as dizziness, difficulty breathing, and wheezing. These symptoms should be taken seriously and warrant professional medical attention.

Infected Horsefly Bites

Although horse fly bites are generally not life-threatening, they can lead to infection in some cases. Watch out for these signs of infection:

  • Increased pain or swelling at the bite site
  • Redness that expands beyond the bite area
  • Pus or discharge from the wound
  • Fever

If you notice any of these signs, it’s essential to seek medical help.

Preventing and Treating Horse Fly Bites

Protection for Humans and Pets

To protect against horse fly bites, apply insect repellent containing DEET on your skin and clothing. Examples of such repellents include:

  • Off! Deep Woods
  • Cutter Backwoods

For pets, use vet-approved insect repellent products.

Protection for Horses and Livestock

Protecting horses and livestock from horse fly bites is essential. Consider:

  1. Fly sheets with zebra stripes – proven to reduce horse and deer fly bites.
  2. Insect repellent – full-body application of synthetic pyrethroids provides full-coverage protection.

Comparison table:

Protection Pros Cons
Fly sheets Effective, non-toxic May require frequent washing
Insect repellent Easy application, multiple-use protection May cause occasional skin irritation

Treatment Options

If bitten:

  1. Clean the bite area with soap and water to reduce infection risk.
  2. Apply antibiotic ointment for further protection.
  3. Use an ice pack to reduce swelling.
  4. Seek medical attention if the bite worsens, causes excessive pain, or swelling does not subside.

In summary, it is crucial to protect humans, pets, horses, and livestock from horse fly bites. Using DEET-based repellents and zebra-striped fly sheets effectively minimize bites, and treatment options like cleaning, applying antibiotic ointment, and using ice packs help manage pain and swelling.

Horse Flies and Disease

Equine Infectious Anemia (EIA)

Equine Infectious Anemia, also known as swamp fever, is a viral disease affecting horses. It is transmitted by blood-sucking insects such as horse flies. Some symptoms of EIA include:

  • Fever
  • Depression
  • Weight loss
  • Anemia
  • Swelling in the lower abdomen and legs


Tularemia, a bacterial infection, can also be transmitted through horse fly bites. Some symptoms of tularemia in horses include:

  • High fever
  • Swollen lymph nodes
  • Decreased appetite
  • Nasal discharge

Comparison Table

Disease Symptoms Causing Agent
Equine Infectious Anemia Fever, depression, weight loss, anemia, swelling Virus
Tularemia High fever, swollen lymph nodes, decreased appetite, nasal discharge Bacteria

Prevention Methods

  • Use insect repellents and fly sheets to protect horses from horse fly bites
  • Remove standing water and control moist areas to reduce horse fly breeding habitats
  • Keep horses indoors during peak fly activity times

Pros & Cons of Prevention Methods

Insect Repellents & Fly Sheets

  • Pros: Can effectively deter horse flies, provide physical barrier
  • Cons: May require regular application, some horses may be sensitive to repellents

Removing Standing Water & Controlling Moist Areas

  • Pros: Reduces breeding habitats for horse flies, helps control other insects too
  • Cons: May not be practical for large areas, requires constant monitoring

Keeping Horses Indoors During Peak Fly Activity Times

  • Pros: Provides protection, reduces horse stress
  • Cons: Limited outdoor time, may not be possible for all horse owners

Managing Horse Fly Populations

Repellents and Traps

Horse flies are notorious for their painful bites, and using repellents can help keep them away from your horses and their living areas. Applying a repellent specifically designed for horses can help deter horse flies from biting. A popular method for capturing these pests is using fly traps designed for outdoor areas, such as stables and yards. Examples of effective traps include:

  • Sticky traps
  • Biting fly traps
  • Solar-powered traps

Environmental Control

Managing the environment effectively can play a crucial role in minimizing horse fly populations. These insects thrive in moist environments, such as marshes and swamps. To reduce their habitat, you should:

  • Remove standing water sources
  • Maintain proper drainage in yards and stable areas

Another method to protect horses is to turn them out at night, as horse and deer flies are daytime biters. Providing shelters or canopy trees far from wooded edges can also aid in protection.

Professional Help

Sometimes, horse fly infestations are beyond personal abatement efforts and require professional help. An exterminator with experience in horse fly control can assess the situation, identify the breeding sites, and recommend the best course of action for getting rid of the pests. They may use a combination of traps, screens, repellents, and other techniques to manage the infestation.

Method Pros Cons
Repellents & Traps Can be effective in reducing horse fly bites May require regular application; some traps harmful to animals
Environmental Natural way to control horse fly populations May be labor-intensive; not always effective alone
Professional Expert, tailored approach to horse fly control Cost of services may be a factor

Remember that managing horse fly populations requires consistent efforts and a combination of methods to achieve the best results.

Reader Emails

Over the years, our website, has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Female Horse Fly


Subject: Is it a fly or bee?
Location: Pierce County, Washington
August 9, 2017 7:42 pm
This bug is about 3/4 of an inch long. It like to fly in the window and play “where is the opening” until I help it out. It buzzes like a fly.
Signature: I don’t care

Female Horse Fly

This is a female Horse Fly, and we believe we have correctly identified it as Hybomitra captonis thanks to this BugGuide image.  Female Horse Flies are blood suckers, and they have been known to bite people if there is no livestock or other prey available.

Female Horse Fly

Letter 2 – Female Horse Fly


Subject: Huge Fly-like insect.
Location: Central Connecticut
August 19, 2017 5:26 pm
Hello, just had this big critter buzz over my head as I opened my garage. It immediately landed on the garage door light and worked its way into the light cover essentially trapping itself. I’d estimate it to be around 1-3/4 inches in body length, easily over 2 inches to the wing tips. Appears very much like a huge fly. Quite a large sucker on it too. Seems to be excreting liquid from its rear as well. I’m located in central Connecticut and have been my whole 36 years. Have never seen a fly of this size. Just sharing my story. Hope its of interest to someone.
Signature: J. Perzan

Female Horse Fly

Dear J. Perzan,
This is a Horse Fly and you can tell by the space between the eyes that she is female.  Female Horse Flies are blood suckers, preying on livestock and large animals like deer, but if there is no preferred prey, they have been known to bite humans.  Unfortunately, we cannot see enough detail in your images to determine a species.

Female Horse Fly


Letter 3 – Female Horse Fly


Subject:  Some type of fly
Geographic location of the bug:  SW Pennsylvania
Date: 05/29/2018
Time: 11:47 PM EDT
Your letter to the bugman:  I’ve recentky been bitten to hell and back by these things. There is a development starting behind my house and all these new bugs have started to come out of the woods since they are clearing the area. The itch
How you want your letter signed:  Doesn’t matter

Female Horse Fly

This is a female Horse Fly and it is possible that habitat destruction has affected its food source.  Female Horse Flies are blood suckers and they might have been feeding on livestock or deer, but they are opportunistic and they will bite humans if no other prey is available.  The two species your individual closely resembles are Tabanus limbatinevris pictured on BugGuide and Tabanus sulcifrons also pictured on BugGuide.

Female Horse Fly

Letter 4 – Female Horse Fly


Subject :  Please help identify this insect
Geographic location of the bug:  I am located in Galloway , Ohio. It’s a suburb of Columbus
Date: 07/13/2021
Time: 05:35 PM EDT
Your letter to the bugman:  Hi Bugman,
Trying to identify what I think is an extremely huge fly. Have never seen one this big. It was easily over an inch long. I am most curious about it. I saw it in Galloway, Ohio the first week of July.
How you want your letter signed:  Tammy Henderson-Pollino

Horse Fly: Tabanus stygius

Dear Tammy,
That is one impressive female Horse Fly.  Female Horse Flies are blood suckers (males only suck the juices of fruits and may take nectar) and it is reported that a bite can be very painful.  The space between her eyes identifies this as a female and male Horse Flies have large eyes that have no space between them.  Thanks to this BugGuide image from Ohio, we are quite certain your individual is
Tabanus stygius and this individual from Texas also posted to BugGuide looks even more like your individual.

Letter 5 – Female Horse Fly


Subject:  Big mean looking fly
Geographic location of the bug:  Southeastern PA – Kennett Square
Date: 08/09/2021
Time: 02:20 PM EDT
Your letter to the bugman:  Hi there bugman,
This extra-large fly was on my window and I want to know if I should be afraid or not.
How you want your letter signed:  Thanks! – Jessica

Female Horse Fly

Dear Jessica,
This is a female Horse Fly in the genus
Tabanus, and we believe based on BugGuide images that it might be Tabanus abdominalis, or possibly Tabanus limbatinevris which is also pictured on BugGuide.  Female Horse Flies are blood suckers that feed off livestock wild animals, but they will bite humans if there is no other prey.


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Horse Fly

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