What Is a Horsefly?
Horseflies are a type of fly that belong to the tabanidae family of insects. The female horsefly depends on blood for nutrition to make eggs. This is because animal blood has a certain protein she needs to develop eggs. Horseflies like feeding on large, dark-colored animals such as horses. But this does not prevent them from biting humans when they get a chance.
The Tabanidae family of insects is made up of about 4,450 species, and about 400 of these species are present in the U.S. Horseflies breed and thrive in wet environments, such as coastal areas.
What Do Horseflies Look Like?
Horseflies are short, sturdy flies with large eyes, segmented antennae, and strong, blade-like mouthparts. Horseflies are usually about 6 to 20 millimeters long (0.25 to 1.25 inches). On some horseflies, the eyes have purple or green bands.
Horsefly vs. house fly
A house fly is much smaller than a horsefly. The largest house flies are about 0.25 inches long. They're usually gray and their bodies are slightly hairy. Their eyes are red. House flies don't have stingers or teeth. They're the most common type of fly in the world.
Are Horseflies Dangerous?
Male horseflies only feed on flower nectar. Although the females also mostly feed on nectar, they have to feed on blood when their mating time comes around. This is when horseflies become dangerous. Female horseflies have to drink blood to reproduce. They mate during the summer, which, coincidentally, is the same time that humans like to go outside in shorts and short-sleeved shirts. This makes humans the perfect horsefly target.
Horseflies have strong and sharp mouthparts that work like scissors when cutting through the skin to get to the blood. The horse fly bite hurts a lot. After mating and feeding on blood, the female horseflies find a damp area to lay their eggs. Common places for horseflies to lay their eggs include:
- Creeks
- Marshes
- Beach dunes
- Pond shores
- Waterfalls
- Termite mounds
The horsefly eggs then hatch into venomous, predatory larvae, or maggots. The larvae make a meal out of small animals like frogs and minnows. They develop into pupae during the winter and become adults at the end of spring. After they become adults, they go on to feed, reproduce, and then die.
Horseflies track their prey by size, color, and smell. They like large, dark-colored animals. When they get close enough to the big, dark object they’ve spotted, they then follow the source of carbon dioxide exhaled by animals when they breathe. Once they've traced the source, they proceed to bite.
Unlike mosquitos and ticks, horseflies are not major disease vectors. This doesn't mean that they can’t transmit diseases — only that they're not as big of a problem as, say, mosquitos and dengue or ticks and Lyme disease.
Horseflies actually benefit the environment. Because they mostly feed on nectar, horseflies help a lot of plants when it comes to pollination. Many plants even rely on horseflies for pollination.
What Are the Signs and Symptoms of a Horsefly Bite?
A horsefly bite mainly causes pain, redness, and minor swelling of the affected area. These bites should go away on their own over a few hours or days. You may also experience other symptoms, including
Horsefly Bite Treatment
If you’ve just been bitten by a horsefly, the following steps may help ease your discomfort:
- Clean the bite site with soap and water.
- Do a cold press by placing an ice pack on the affected area for 10 minutes to ease the swelling.
- Raise the affected area to manage the swelling.
- Try not to scratch the bite, which could lead to infection or a blister. If a child has been bitten, consider cleaning and trimming their fingernails.
- Avoid applying substances considered to be home remedies (such as vinegar or sodium bicarbonate) to the affected area. They may not help.
- Use over-the-counter medications to manage pain and discomfort.
- If you're itching a lot, talk to your doctor about the best treatment (creams or medications) to relieve the itch.
When to Call Your Doctor
In some cases, you may get severe symptoms. If you notice any of the following, get immediate help:
- Dizziness
- Wheezing or difficulty breathing
- Problems with swallowing
- Swelling in the throat, mouth, or face
- Increased heart rate
- Loss of consciousness
- Vomiting
- Any symptoms of infection, such as pus at the bite site, fever, or swollen glands
How to Get Rid of Horseflies
To avoid horsefly bites in the first place, here are some strategies you could try:
White clothing. Because horseflies look for large, dark-colored objects when hunting prey, wearing a white shirt or clothing may make you unattractive to horseflies. However, if you are in an area known to have ticks, this may not be the best idea. Removing the target on your back for horseflies may make you easy prey for ticks, which are attracted to the color white.
Body paints. Having brightly colored body painting may help to throw off horseflies because they seek out dark colors. Just note that although such body paints may be able to keep horseflies at bay, most are used for specific cultural reasons among indigenous communities on various continents.
Traps. Laying horsefly traps can be effective when it comes to smaller areas such as yards, swimming pools, and camping sites. This method also might work if you're trying to keep horseflies away from cattle in a confined place. An example of a trap that works is hanging black, shiny, sticky balls that attract horseflies as they're moved by the wind. Another option is a malaise trap — a large piece of netting that catches flies simply by being in their flight path.
Manipulating the environment. This involves clearing bushes or woods in residential areas and draining damp areas to eliminate breeding places for horseflies. This can be effective because horseflies will lay their eggs only in wet areas.
Horsefly repellent
Insect repellents offer some degree of protection against horseflies. However, you may not get the same results as you do with mosquitos or ticks, even if your repellent contains DEET. You also can treat your clothes with the chemical permethrin. The treatment should last through several wash cycles. But don't apply permethrin directly to your skin.
Takeaways
Horseflies are relatively large flying insects, and their bites are painful. The male horsefly feeds on plants, but the female needs blood to reproduce. Horseflies will bite livestock such as horses and cattle, and they'll bite humans as well. Horsefly bites don't transmit disease as often as mosquito or tick bites can, but they hurt. A cold compress and over-the-counter pain reliever might make you feel better. Some people have allergic reactions to the bite. If you have trouble breathing, are dizzy, or feel your throat swelling, get help right away.
Horsefly FAQs
What attracts horseflies?
The female horsefly is attracted to large, dark shapes and movement. They also are drawn to carbon dioxide, which humans and animals exhale. Horseflies may gather in shady areas, waiting for prey to pass by.
How Can I Prevent Horsefly Bites?
If you're in an area with horseflies, wear long sleeves and long pants while outside. Wearing light-colored clothes might help keep horseflies away but can attract ticks. An insect repellent that contains DEET, citronella, or geraniol might offer some protection. You also can treat your clothes with a chemical called permethrin. But you should never apply it directly to your skin.
Are horsefly bites harmful?
For most people, a horsefly bite is a painful nuisance. The bite may itch, turn red, and hurt. The area around the bite may swell. However, some people are allergic to horsefly bites. If you have trouble breathing or swallowing, a fast heart rate, dizziness, or other signs of a severe allergic reaction, get help right away.