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Why Do Horseflies Bite, Will They Chase You? 7 Facts

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Recently my neighbor’s son showed us his arm covered with horsefly bites. He swears horseflies chase him anytime he gets within a mile of one. His proclamation made me wonder why horseflies bite and if they really chase people.

Horseflies bite to ingest blood which is rich in protein. The protein is needed to develop their fertilized eggs. Only females need to bite since the males don’t produce eggs. And yes, horseflies will chase you down to get their meal. So be wary of them.

If horseflies have chased you, you understand how unpleasant an experience is, but do they bite and chase some people more than others? This is one of many questions surrounding horse fly behavior I answer.

picture of a horsefly on a persons' arm.

Horsefly bites

Horsefly bites hurt and often cause swelling, itchiness, and a burning sensation. It’s even possible that a bite from a horsefly can bruise you. The good thing is that horsefly bites don’t typically cause long-term health issues in humans.

Horseflies are dangerous to horses because they release anticoagulants from their saliva when they bite to keep the blood flowing. The saliva can carry and transmit equine infectious anemia, which is fatal in some horses.

picture of a boy running from horseflies,

Will horseflies chase you?

First and foremost, it’s essential to highlight the fact that horseflies can absolutely chase you. Often when female horsefly lights on you and is brushed off before satisfying its protein needs, it will go right back and try again.

If you start moving away, the persistent pest will chase you. Besides determination to get blood, there are other reasons horseflies pursue people. For one, they are attracted to moving objects, especially dark moving objects that are warm.

So if you start moving away, they follow you. Motion is a constant observed in most people that horseflies start chasing. People running in areas where these flies are common are likely familiar with incidents of this sort.

Sometimes I run at a park surrounded by trees with a pond in the middle. One day a horsefly got after me, and I couldn’t believe it continued to harass me lap after lap; each lap was 8 tenths of a mile.

Finally, I passed a group of walkers, and the horsefly decided to harass them instead of me. Being chased frequently occurs when activities are done in warm weather.

Their activity is heightened during the heat of the day. And it seems horseflies enjoy hunting in warm weather more than cooler. And from my personal experience running, I know they like warm, sweaty bodies.

Along with motion and heat is the fact that anyone running, cycling, or doing some other physical activities typically releases pheromones and sweat that attract horseflies.

Pheromone is a general term that describes chemicals produced and released in the air by animals or insects that affect the behavior of others of its species. Mammals often secrete smells that attract mates.

Someone who’s fully engaged in their workout may run past a few horseflies, and they take off after the person when they recognize the scent of pheromones and sweat.

Horsefly chases are certainly no fun, and their bites can be quite painful because their bites tear the skin instead of piercing through it. You can, however, take steps to lower the risk of horseflies chasing you.

Things like limiting your exercise to periods when it’s cold, utilizing fly spray, and even wearing lighter colors are all capable of detracting horseflies from chasing you. These tips are certainly worth considering if horseflies regularly pursue you.

Picture of a two year old thoroughbred horse.

Why do horse flies bite when you are wet?

Our horse barn is over 100 yards from our swimming pool, yet we constantly have horse flies around the pool, and they seem to follow and bite the wet swimmers. I know they are attracted to movement and carbon dioxide, but why do horse flies bite when you are wet?

One theory is that horse flies are able to detect the lactic acid in sweat, which is more concentrated when you are wet. However, this doesn’t apply to wet swimmers. Another possibility is that horse flies are simply attracted to the moisture on your skin.

And they’re around swimming pools because there is some standing water nearby that is providing a breeding ground for them. In some cases, horse flies may also be attracted to the chlorine in pool water.

If you have horse flies around your swimming pool, you may want to take steps to eliminate any standing water sources that they could be breeding in.

Why are horseflies so aggressive?

Horseflies are known for their aggressive nature, which is due to their blood diet. The more time they spend around humans and other animals, the hungrier they get and the more aggressive they become when looking for food.

Female horseflies are aggressive; they fly around looking for blood meals that will provide the protein needed to grow their fertilized eggs; males just hang out on plants.

Once a horsefly chooses a victim, they use its powerful jaws to rip loose skin and extract blood from animals and humans. Most horsefly victims are livestock with thick skin, so their bite’s force must be powerful.

And when horseflies bite humans, they don’t take it easy; they use the same biting power on us as they do a thick-skinned animal.

The force and ripping action of horsefly jaws are the reason their bites are so painful. Male horseflies survive on plant pollen and don’t bite humans.

How do you keep horse flies from biting you?

We recently had some guests over and knew beforehand they would want to check out some of the horses we had in our barn. Knowing this, I took steps ahead of time to reduce the risk of horseflies aggravating us.

To keep horseflies from biting, it’s critical to use horsefly repellant, remove standing water, keep your barn clean of manure and debris, use horsefly traps, and burn citronella candles in the surrounding areas. But don’t burn candles in your barn.

Horseflies are a pain for both you and your horses. There are many products that will help to prevent them, including commercial horsefly sprays, masks, fans, or fly boots. I’ve written an article about these items- you may find helpful. Check it out here: Do Horse Fly Masks and Fly Boots Work? Which Ones Are Best?

picture of a horsefly,

Can horse flies bite through clothing?

Some people believe wearing long sleeves, shirts, and pants covering most of their skin will keep horseflies from biting them. Clothing may deter some insects, but not horseflies; they can bite through clothing, fur, and animal hide.

Why do horseflies bite me and not others?

Horse flies never seemed to bite my father, but they loved me. I figured it was because he was a smoker and coffee drinker, and the insects didn’t like his scent. But, after doing some research, I learned something different.

So why do horse flies bite me and not others? There are a few reasons. First, horse flies are attracted to movement. Well, I was always running and playing, so if you’re running or playing sports, you’re more likely to catch their attention than someone who is sitting still.

Second, horse flies are attracted to dark colors. So if you’re wearing dark clothes, you’re more likely to be targeted than someone who is wearing light-colored clothes. Finally, horseflies are attracted to areas of the skin that are exposed.

So if you’re sweating or have an open wound, you’re more likely to be bitten than someone who is dry and covered up. If you don’t want to be bitten by horseflies, the best thing you can do is to avoid their favorite targets: movement, dark colors and exposed skin.

What do horse flies hate?

Fighting horseflies effectively starts by knowing your enemy. In other words, what do horseflies hate and will keep them at bay? Are there certain smells or colors that they avoid?

Horseflies hate some herbs such as eucalyptus, rosemary, basil, lemongrass, and clove. They also seem to avoid Avon’s Skin-So-Soft, apple cider vinegar, white vinegar, and citronella. Some of these scents are used in commercial horsefly sprays and effectively ward off horseflies.

Picture of flypaper in a horse barn.

Are horseflies good for anything?

We know horseflies transmit fatal diseases, aggravate animals and humans, and pack a painful bite. But there is typically some utility from even the most mundane things in our life. So I wondered what benefits horseflies provide.

Horseflies are not good for anything. You can stretch your imagination and claim they are part of the ecosystem food chain. However, as a food source, its impact is negligible. Yes, birds eat horseflies, but not enough to make a meaningful impact on their diet.

Picture of horses in a pasture

Where do horseflies live?

It seems horseflies are everywhere during the summer, and a couple of them frequently disrupt our guests at the swimming pool. Their presence made me wonder if they live nearby because our horse barn is over 100 yards away from the pool.

Horseflies are most active in the summer between May and September; they congregate around horse barns and pastures. They thrive in warm, moist areas. Stagnate water and manure or two favorite locations for immature horseflies to live.

Our swimming pool is behind our house but surrounded by a pasture on three sides. The pool and the surrounding area have a lot of standing water that attracts insects, and our guests’ movement also plays a role in the presence of horseflies around our house and swimming pool.

Below is a YouTube video that explains why horseflies are so aggressive.


Do homemade horsefly sprays work?


Yes, and some homemade horse fly sprays are as effective as commercial sprays. Plus, most are safer and cheaper to make than retail fly sprays.
You can learn more about homemade horsefly sprays in this article.

Do you know why horses attract horseflies?

Flies are attracted to large, warm, and dark moving objects, horses and cows primarily, but humans in dark clothing will suffice.
If you want to read more about what attracts horses, check out this article: Why Do Horses Attract Flies? Number 2 May Surprise You