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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.

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?

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.

picture of a horsefly,

Why do horseflies bite me and not others?

Horseflies are particularly active during their mating season, which is in the summer. And they always seem to bite my neighbor’s son. So I wanted to find out if there is a reason they bite some people and not others.

Horseflies bite some people more than others, motion, moisture, dark colors, and certain scents attract horseflies to you. Kids or adults wearing dark clothing, specifically dark blues, moving quickly, and sweating, are prime targets for horseflies to attack.

If a person is sitting quietly dressed in bright clothing, and another person is running around sweating, dressed in a dark blue outfit, they won’t be treated the same by horseflies. The one running around will be bitten more often.

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 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.

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.

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