How long can a horse fly live without food

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 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.

ENTFACT-511: Horse Flies and Deer Flies  |  Download PDF

by Lee Townsend, Extension Entomologist 
University of Kentucky College of Agriculture 

Horse flies and deer flies are bloodsucking insects that can be serious pests of cattle, horses, and humans. Horse flies range in size from 3/4 to 1-1/4 inches long and usually have clear or solidly colored wings and brightly colored eyes. Deer flies, which commonly bite humans, are smaller with dark bands across the wings and colored eyes similar to those of horse flies. Attack by a few of these persistent flies can make outdoor work and recreation miserable. The numbers of flies and the intensity of their attack vary from year to year. 

Numerous painful bites from large populations of these flies can reduce milk production from dairy and beef cattle and interfere with grazing of cattle and horses because animals under attack will bunch together. Animals may even injure themselves as they run to escape these flies. Blood loss can be significant. In a USDA Bulletin 1218, Webb and Wells estimated that horse flies would consume 1 cc of blood for their meal, and they calculated that 20 to 30 flies feeding for 6 hours would take 20 teaspoons. This would amount to one quart of blood in 10 days. 

Female horse flies and deer flies are active during the day. These flies apparently are attracted to such things as movement, shiny surfaces, carbon dioxide, and warmth. Once on a host, they use their knife-like mouthparts to slice the skin and feed on the blood pool that is created. Bites can be very painful and there may be an allergic reaction to the salivary secretions released by the insects as they feed. The irritation and swelling from bites usually disappears in a day or so. However, secondary infections may occur when bites are scratched. General first aid-type skin creams may help to relieve the pain from bites. In rare instances, there may be allergic reactions involving hives and wheezing. Male flies feed on nectar and are of no consequence as animal pests. 

Horse flies and deer flies are intermittent feeders. Their painful bites generally elicit a response from the victim so the fly is forced to move to another host. Consequently, they may be mechanical vectors of some animal and human diseases. 

LIFE CYCLE

The larvae of horse fly and deer fly species develop in the mud along pond edges or stream banks, wetlands, or seepage areas. Some are aquatic and a few develop in relatively dry soil. Females lay batches of 25 to 1,000 eggs on vegetation that stand over water or wet sites. The larvae that hatch from these eggs fall to the ground and feed upon decaying organic matter or small organisms in the soil or water. The larvae, stage usually lasts from one to three years, depending on the species. Mature larvae crawl to drier areas to pupate and ultimately emerge as adults. 

PROTECTING YOURSELF

Deer flies are usually active for specific periods of time during the summer. When outside, repellents such as Deet and Off (N-diethyl-meta-toluamide) can provide several hours of protection. Follow label instructions because some people can develop allergies with repeated use, look for age restrictions. 

Permethrin-based repellents are for application to clothing only but typically provide a longer period of protection. Repellents can prevent flies from landing or cause them to leave before feeding but the factors that attract them (movement, carbon dioxide, etc.) are still present. These flies will continue to swarm around even after a treatment is applied. 

Light colored clothing and protective mesh outdoor wear may be of some value in reducing annoyance from biting flies. In extreme cases, hats with mesh face and neck veils and neckerchiefs may add some protection. 

PROTECTING ANIMALS

Horse flies and deer flies can be serious nuisances around swimming pools. They may be attracted by the shiny surface of the water or by movement of the swimmers. There are no effective recommendations to reduce this problem. 

Permethrin-based sprays are labeled for application to livestock and horses. These insecticides are very irritating to the flies and cause them to leave almost immediately after landing. Often, the flies are not in contact with the insecticide long enough to be killed so they continue to be an annoyance. These flies will swarm persistently around animals and feed where the spray coverage was not complete (underbelly or legs) or where it has worn off. Repeated applications may be needed. Check the label about minimum retreatment intervals. Pyrethrin sprays also are effective but do not last as long as permethrin. 

Horse flies and deer flies like sunny areas and usually will not enter barns or deep shade. If animals have access to protection during the day, they can escape the constant attack of these annoying pests. They can graze at night when the flies are not active. 

CONTROL

It is difficult to impossible to locate and/or eliminate breeding site of horse flies and deer flies. They breed in environmentally sensitive wetlands so effects of drainage or insecticide application on non-target organisms or water supplies is a concern. Also, these insects are strong fliers that can move in from some distance away. Breeding sites may be very extensive or some distance away from where problems are occurring. 

Fortunately, horse flies and deer flies are sporadic problems for specific times of the year. Some adaptation in behavior or use of repellents can allow enjoyment of the outdoors. 

Issued: 01/00 
Revised: 01/00 

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication. 

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE! 

Images: University of Kentucky Entomology