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Facts About Horse Flies

Horse flies (Tabanidae) are large, aggressive flies, and are very spry fliers. They are among the largest of all the fly species, and there are about 3,000 species of Horse fly around the world. Females bite humans and other animals (notably horses and other livestock) in search of blood meals. Horse flies and Bot flies are also referred to as "gadflies."

If you find horse flies annoying, just remember you're not the first. Ancient Greek literature (Aeschylus) mentions people being driven insane by aggressive Horse flies! The Vikings were also wary of them.

But not to worry. Read on for the most important facts about Horse flies and learn how you can put preventive measures in place to keep you and your family safe.

What Do Horse Flies Look Like?

Horse fly

Horse flies range from yellowish-brown to dark grey to blackish in color and typically measure about 3/4" to 1.25" in length. Their heads are huge in relation to the rest of their bodies, and they are hairy all over, bearing a slight resemblance to honey bees. As with all other true flies from the Diptera order, they only have one pair of wings, however, which come covered with lightly colored, wispy spots.  

Horse flies are also known for their large, colorful eyes.

Horse Flies vs. Deer Flies

Horse flies are often confused with Deer flies, which also commonly bite humans. Deer flies also have brightly colored eyes like Horse flies, but are somewhat smaller. They feature distinguishing dark bands across their wings.

Where do Horse Flies Come From?

Horse flies can be found just about anywhere in the world except for the polar extremes and some islands, like Hawaii. These flies prefer warm areas with enough moisture for breeding, but can also exist in a wide variety of habitats, including deserts and mountain meadows.

Horse flies are exclusively outdoor dwellers and do not feed or seek harborage indoors. You may occasionally encounter one who has accidentally wandered inside through an open window or door, in which case a flyswatter or reliable indoor and outdoor fly spray can make quick work of it. 

Horse Fly Habits

These flies are mostly found in valley pastures near creeks and streams, preferring more warmth and dampness, and areas where livestock and humans can be found outdoors.

Horse flies do not only prefer the outdoors (especially near pools of water, like mosquitoes). They also prefer sunlight, are most prevalent in the summer months, and tend to avoid dark, shady areas. Horse flies do not come out at night. 

Adult Horse flies feed primarily on nectar and plant excretions. Only the females bite, as they have strong, incisor-like mouthparts, while males have feeble mouthparts. Females (again, like mosquitoes) bite animals and humans to obtain protein in the form of a blood meal in order to be able to produce eggs. Horse fly larvae develop in aquatic/semi-aquatic environments, where they are predators of smaller life forms.  

What Attracts Horse Flies?

Female Horse flies detect humans and animals by colors, and movements, they are attracted to shiny objects, warmth, sweat, and exhaled carbon dioxide.  

Can Horse Flies Bite?

Female Horse fly bites are very painful, but worse, these flies can transfer bacteria and blood contaminants from one host to another. They can make livestock and humans extremely sick, and even cause reduced growth rates and milk output in unsheltered cattle. Effects are worse if a bitten human or animal has an allergy.

Horse fly bites on humans can appear red and raised (like a welt), and can also inflict rash, dizziness, weakness, and wheezing. 

If you, a family member, or pet are bitten by a Horse fly, immediately wash well and apply a cold compress. As with mosquito bites, scratching will make the itching and effects worse. Symptoms from the bite should go away within a few hours, but if an infection occurs, seek medical attention.

Will Horse Flies Bite Your Dogs?

The female Horse fly's scissor-like mouth can inflict painful bites not only on humans, but also on your dog, even though the effects and minor irritation are short-term, there still exists the danger for your pets that come with all biting pests: the spread of bacteria and other blood contaminants. Larger dog breeds are the most susceptible to Horse fly bites, and the most vulnerable areas to get bitten tend to be the abdomen, legs, and neck. 

The Horse Fly Life Cycle 

Female Horse flies lay their eggs under gravel or vegetation, within some proximity to a water source. When the eggs hatch, the whitish, spindly larvae move into the nearby water or damp soil, during which time they feed on small insects and even reptiles. The Horse fly larval stage can last up to a year, and at that point, the larvae dig themselves into the soil in order to pupate. After one to two weeks as pupae, and another 3 to 10 weeks as developing adults, the full-grown adult Horse flies emerge. Adults live from 30 to 60 days.

Helping Prevent a Horse Fly Problem Outdoors

Suburban Horse fly problems are less common than in less-populated, rural areas that may have grassy, open fields and livestock nearby. Pest control products would ideally not be used until all other methods have been implemented and you're still seeing a Horse fly problem. 

Common remedies for flies and other flying insects outdoors include citronella candles and UV bug zappers. Horse flies are not attracted to trash and animal carcasses, but keeping your yard as free from standing water as possible will help keep them to a minimum (and mosquitoes, as well!).

Fly Killer Treatments

Pest Control Products

Try an effective plant oil-based indoor fly killer for spot-treatment of Horse flies, like Maggie's Farm Home Bug Spray, or Maggie's Farm Flying Insect Killer. Plants don't like flies and other bugs any more than you do, and the natural oils they produce to protect themselves are amazingly effective at killing and repelling bugs of all sorts. For effective personal protection against flies (and mosquitoes), try plant oil-based Maggie's Farm Natural Insect Repellent.

For longer term, more thorough coverage, you can treat wider areas of your lawn with effective hose-end plant oil-based pest control products like Maggie's Farm Yard Bug Spray

Always carefully follow any directions on pest control product labels, including for storage and disposal.

Find more information here:

The Best Indoor Fly Killer Spray

Tips for a Bug-free Cookout

How to Use a Yard Bug Spray

How to Keep Pests Out of Your Lawn Naturally

How do you control Cluster flies in your home and yard? Leave us a comment! We want to hear your tips and tricks! 


For scientifically-tested, effective fly control in your home that is friendly to the environment, try Maggie’s Farm pest control products. Our promise is that our plant and mineral-based products are developed by scientists and seasoned pest control professionals to be the most effective.

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