Horse Flies 101: What You Should Know About Horse Flies

Horse Flies 101: What You Should Know About Horse Flies

Unfortunately, there is no way you can avoid flies if you have a horse around. While the typical flies that hang around your horse’s eyes and face are certainly bothersome, they are not particularly dangerous unless you have a serious fly problem. However, the horsefly is another thing entirely and is worth becoming familiar with if you want to protect your horse from a painful bite.

What are horseflies? A horsefly is significantly larger than a housefly and lives on the blood of large animals – especially horses and cattle. They procure their meals using their razor-sharp mandibles, which can cause a significant sting, whether horse or human is afflicted. Horseflies prefer warm, humid climates and breed along marshes and other bodies of water. 

Keep reading to learn everything you need to know about these painful pests, including how they feed and how to control them. 

Horsefly vs. Housefly 

You probably see flies around your horse all the time – virtually all livestock attract these pests, and there is little that can be done aside from physical (masks) and chemical (spray) barriers. If reading about the harm that can be caused by horseflies concerns you, don’t fret.

The flies that you see swarming your horse in the Summer are most likely basic houseflies. Houseflies do not bite but instead eat soft organic material and are especially attracted to the liquid secretions from a horse’s eyes. Though they do not bite or cause pain, they are very irritating.

The easiest way to tell the difference between a horsefly and a housefly is by looking at the size of the insect. Horseflies are one of the largest species of fly, measuring from ¾ of an inch all the way up to 1 ¼ inches. This is significant compared to the housefly, which has an average length of only ¼ of an inch. 

In addition to the size difference, there is also a difference in the eyes of the housefly and the horsefly. Horseflies have larger eyes, which are emerald or black, while the eyes of a housefly are somewhat smaller (even when adjusted for body size) and are often red. 

The Horsefly’s Ideal Environment

If you’ve never seen a horse fly, that is likely because you live in a climate that is not suitable for them. While mature horseflies can travel significant distances to feed, their breeding requires wet, marshy conditions. The female horsefly typically lays her eggs on a plant along the shore or edge of a body of water, like ponds, streams, or wetlands.

Because horseflies are primarily active in the Summer months, that means if you live in a dry (i.e., Mediterranean or desert) climate, you may not be afflicted by horseflies at all. Consider yourself (and your horse) lucky!

How To Get Rid Of Horseflies 

If you live in an area that is suitable for the horsefly population, there isn’t a lot you can do to control the population aside from trapping. Horseflies are primarily a Summer nuisance and are active during the day. Horseflies are attracted to movement, warmth, and carbon dioxide – in other words, they are attracted to living beings. An animal that is alive and breathing will have warmth and will be expelling carbon dioxide; there is no way to disguise that. 

Horseflies don’t usually enter areas of deep shade like barns; this is because they prefer to hunt and fly in the sunshine and are attracted to light. Some horse owners who are especially concerned about horsefly bites go so far as to confine their horses during the day, turning them out after the sun goes down to graze and exercise. This may sound like an extreme measure, but some horses are particularly sensitive to bites

Can horseflies be trapped?

There are a number of traps available on the market to control flying insects – some report success with horseflies, and some don’t. It is certainly worth the trial and error if you have a pest problem. Traps that work by emitting light may work better than traps designed for houseflies – after all, horseflies and houseflies are not attracted to the same things.

There is one type of trap designed specifically for biting flies, and that is the Bug Ball. This is a large inflatable black ball that is to be hung approximately 4-5 feet above the ground. The dark color, slight movement, and warmth (created when the dark surface absorbs the sunlight) all work together to attract horseflies.

The Bug Ball kits come with a sticky adhesive “paint” that is used to coat the surface of the ball, trapping the insects as they land. This type of trap has had great reviews, and many report success with it. You can check the price here on Amazon. While some kits advise hanging the ball in a barn or other structure, I would suggest hanging it from a tree, fence post bracket, or shepherd’s hook outside where it is likely to attract the most flies. 

The Life Cycle Of A Horse Fly

Female horseflies can lay anywhere between 25 and 1,000 eggs at a time. They lay the eggs on vertical plants near bodies of water so that when the eggs hatch, the larvae fall off the plant and into the mud, where they can thrive in their ideal environment – mud. The larvae stage of a horsefly is quite long – they can remain in this stage for anywhere from one to three years.

In the mud, they primarily feed on decaying plant matter until they are ready to pupate. During pupation, they remain in their “cocoons” for one to two weeks, after which they emerge as young horseflies. These young horseflies reach maturity at a rapid pace, and fully grown adults live only for 30-60 days.

Do Horsefly Bites Hurt?

If you’ve never been bitten by a horsefly, you might wonder whether you would feel the bite or whether it would be painless, as is the “bite” of a mosquito. Consider yourself lucky to have not experienced a horsefly bite because the answer is yes – they do sting! The horsefly bite is considered to be the most painful of any biting fly, and certainly in other flying insects like the mosquito. There are a couple of reasons for this.

The first is that horseflies do not contain any anesthetic in their saliva (unlike mosquitoes). When a mosquito attacks you, it first secretes an anesthetic to numb your skin before puncturing. You get no such kindness from a horsefly – there is no numbing effect at all.

The second reason that a horsefly bite will cause pain is because of the way in which it punctures the skin. A mosquito will poke into the skin and create a small hole. A horsefly does not have this type of anatomy – instead, it has serrated scissor-like mandibles. It slices through the skin with its mandibles to create a small laceration. Once the blood begins to pool, it uses its sponge-like mouth to feast. 

If you are fortunate enough to have not noticed the bite of a horsefly, you will probably notice the welt it leaves behind. Because the bite has created a wound, the site will become red and inflamed as your immune system works to eliminate pathogens and repair the skin. The welt will likely last for a few days and may be tender to the touch. 

Do both male and female horseflies bite?

Many insects and spiders will have great differences between genders – including differences in behavior, appearance, and even lifespans. This is true for horseflies as well. Only female horseflies bite, and this is because the protein in the blood on which they feed directly affects their ability to reproduce. The more blood protein a horsefly ingests, the higher her egg count.

Male horseflies do not feed on blood and, in fact, do not even have the mouth anatomy required to do so. Male horseflies are, therefore, harmless to animals, feeding on nectar and pollen.

Can you be allergic to horsefly bites?

While not nearly as common as bee sting allergies, it is possible to be allergic to horsefly bites. In the case of an allergy, reactions may include a rash that extends past the site of the bite, hives, significant swelling, dizziness, and even breathing problems. If you suspect you were bitten by a horsefly and are experiencing any of these more serious reactions, seek emergency help right away.

The Nuisance Of Horseflies

Horseflies can be an absolute pain, and we should consider it fortunate that they are primarily a seasonal problem. While the occasional bite is simply a nuisance to most, some horses, people, and cattle can be particularly sensitive to the horsefly bite. If horseflies are more than a little bothersome to you and/or your livestock, consider a trap designed especially for biting flies, like the Bug Ball mentioned above. Using something like this, along with a potential night-time grazing schedule, should bring you significant relief.

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