Discover Why Horseflies Bite and How to Treat a Bite

Horsefly sitting on a branch.
© ploypemuk/Shutterstock.com

Written by Telea Dodge

Published: September 8, 2023

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Flies are one of the oldest living creatures on the planet Earth. Their ancestry dates back over 250 million years. Humans have never lived without flies, so we have always had to deal with the consequences of the biting ones. Horseflies, in particular, have been bothering us and biting us for as long as the human race can remember. Today, we’ll talk about why these insects bite – and what you can do about it when they do.

What is a Horsefly?

Horsefly

You can see the two distinct wings and sharp mandibles of this female horsefly.

©iStock.com/guraydere

Horseflies descend from the insect order Diptera and are in the family Tabanidae. These flies live in all parts of the world except for Iceland and Antarctica. A horsefly is a true fly, with two wings and a short life cycle. An adult horsefly only lives for 30-60 days. That’s 1-2 months! A horsefly can reach a top speed of 90 miles per hour with its tiny body. Each fly only weighs up to 12 milligrams and measures up to 1.25 inches long.

Life Cycle of a Horsefly

The life cycle of a horsefly begins in the larval stage. The larval stage of a horsefly can last up to one year. A mother horsefly lays her eggs under the cover of some sort of vegetation or gravel. The eggs need to be near a water source, such as a warm swamp or marsh. After the eggs hatch, the larvae make their way to that water source or into damp soil. The white larvae then feed on small insects and hang out until they’re ready to pupate. The larvae burrow into the soil and spend one to two weeks as pupae and then begin to transform into their adult stage. This transformation can take as little as three weeks and as many as ten. Once the horsefly emerges as an adult, it will live for 30-60 days.

Horsefly Diet

Horsefly with spectacular eyes feeding on a human.

A female horsefly feeds on human blood during the breeding season.

©JumpingSpiderss/Shutterstock.com

Adult horseflies have separate diets based on their sex. Male horseflies are nectar and pollen feeders. They spend their entire adult lives peacefully feeding on the bounties of nature. Female horseflies also feed on nectar and pollen but require blood meal in order to reproduce.

Why do Horseflies Bite?

Only female horseflies bite, and it’s a part of the horsefly life cycle. Horseflies only bite or feed on blood during their breeding and mating seasons. Outside of this season, all horseflies are happy to consume a diet of only plant pollens and nectars. When breeding season arises, the female horsefly must supplement her diet with blood to have a successful reproductive cycle.

What do Horseflies Bite?

Horseflies get their blood meal mostly from large mammals, such as horses, cows, camels, and humans. You can imagine from the name that horseflies prefer the blood of horses, and if you’ve ever been in a horse pasture in high summer, you’ll see this is true. Horseflies bite with a set of serrated mandibles. It’s not a singular bite, but more of a sawing motion, which is probably why it hurts so much when it happens. Your skin is being sawed open to promote blood flow. Small blood vessels near the surface of your skin burst and give the horsefly her meal.

What Does a Horsefly Bite Feel Like?

Most people describe horsefly bites as painful, irritating, and itchy. The pain presents at the time of the bite and can usually be described as an itching and stinging pain. The initial bite is followed by swelling and itching around the affected area. Sensitive groups may develop a bruise or welt at the site of a horsefly bite. People with allergies to the bites may develop rashes or experience anaphylaxis. For most people, the symptoms are minor and go away within a few hours or a few days. The most lingering side effect will be a raised and itchy bump at the site of the bite.

How to Treat a Horsefly Bite

Horsefly sitting on the human skin

Clean a fresh horsefly bite with soap and water and then ice it to prevent swelling.

©Geza Farkas/Shutterstock.com

If you get bitten by a horsefly, don’t panic. Treatment of the bites is quite simple and most side effects of the bite will only last a couple of days. The first thing you want to do is clean the affected area with soap and water. We recommend cold water. You can then place an ice pack on the area to reduce and manage swelling. You’ll only need to do this for a few minutes – five to ten. Finally, try not to scratch the bite site or apply vinegar or other home remedies to the bite. Horsefly bites are not severe and many of these home remedies are ineffective. You will not need the help of a hospital or medical professional unless you suffer a moderate to severe allergy or the pain and itching do not go away for several days.

Are Horsefly Bites Dangerous?

Comtois horse in the meadow

Horses face the largest risk from horsefly bites.

©Grimplet/Shutterstock.com

Horsefly bites are much more irritating than they are dangerous – for humans, anyway. Unlike mosquitos and other blood-feeders, horseflies aren’t big transmitters of disease. The greatest risk is actually posed to your horses. Horseflies carry and can transmit an equine disease known as Equine Infectious Anemia – or “swamp fever” – to horses. Unfortunately, this disease can be fatal. However, many horses live long, happy lives after surviving the acute phase of the infection. Only equine mammals are impacted by this disease, including donkeys, zebras, mules, ponies, and horses. This viral disease has no vaccination or treatment.

How to Prevent Horsefly Bites

There are a number of things you can do to avoid a horsefly bite. We’ve included a helpful list of actions to take to avoid getting bitten by these flies.

  • Wear long sleeves and long pants when outside, especially in damp or swampy areas with still water.
  • Avoid the use of perfume. Sweet smells draw horseflies.
  • Light colors are better than dark colors. Horseflies are drawn to large, dark moving shapes.
  • Wear insect repellant. Several natural and chemical insect repellants advertise effectiveness against horseflies.
  • Avoid walking through long grass.
  • Wear loose-fitting clothing.

Benefits of Horseflies

These big flying insects aren’t all bad. Since all horseflies feed on pollen and nectar, they are actually wonderful pollinators for your natural environment. They also serve as a wonderful key source of nutrition for many other animals, such as birds and bats. Horseflies in their larval stage provide adequate nutrition to a variety of fish and other aquatic species. Since the horsefly is not a common vector for disease, it rarely has any sort of economic or health risk. Most people and farmers experience zero loss from the horsefly. To simplify: the majority of people who complain about horseflies are people who are being bitten by them. They serve a greater role in the ecosystem than the level of nuisance we experience from their presence.

Other Biting Flies

deer fly

Deer flies are in the same family as horseflies and also deliver a powerful bite.

©Paul Reeves Photography/Shutterstock.com

Horseflies are not the only biting flies. Several other species of flies can and do bite. In the United States, there are several types of flies that bite. We’ve included a short list of these flies below.

  • Deer flies
  • Horseflies
  • Black flies
  • Stable flies
  • Snipe flies
  • Sand flies
  • Yellow flies
  • Biting midges

The most common of these across the United States are the first three on the list. Yellow flies mostly only live in the southeastern United States and stable flies spend more time biting horses than humans. Sand flies might be one of the spookiest flies on the list for their strong and painful bite and their diet of mammals and reptiles.

Summary

Aggressive Animal: Horsefly

Horseflies play an integral role in our natural environment.

©Achkin/Shutterstock.com

Horsefly bites can be painful and itchy and there are some really good ways to prevent and treat them, such as wearing long clothing, avoiding sweet perfumes, and icing a fly bite right after it occurs. Overall, horseflies benefit the natural environment more than they hurt it by being key pollinators and food sources for several animal species.


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About the Author

Telea Dodge is an animal enthusiast and nature fiend with a particular interest in teaching a sense of community and compassion through interactions with the world at large. Carrying a passion for wild foraging, animal behaviorism, traveling, and music, Telea spends their free time practicing their hobbies while exploring with their companion dog, Spectre.

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