Horsefly Bites: Identification And Treatment - Medical News Today

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Medical News TodaySubscribeWhat to do about a horsefly bite

Medically reviewed by Helen Chen MCMSc, PA-C — Written by Markus MacGill — Updated on May 1, 2025

Identifying a bite
Is it dangerous?
Severe reactions
Treatment
Prevention
FAQs
Summary

Horsefly bites can be painful, but they are not usually dangerous. Covering up with clothing is one way to prevent bites, but horseflies can often bite through fabric. Cleaning the area and applying a cool compress may help ease the pain.

Avoiding horseflies outdoors in summer can be difficult, and horsefly bites can be more painful than bites from other bugs. This is because they have saw-like mouthpieces they use for biting. Also, they do not inject any type of anesthetic when they bite.

While painful, a horsefly bite will rarely lead to severe complications. In rare cases, however, a person may have a severe allergic reaction to a horsefly bite and need medical attention.

This article describes the most effective treatment for horsefly bites, how to identify them, and ways to prevent them.

Identifying a horsefly bite

Horsefly bites are painful compared with other insect bites. They can also be slow to heal. This is because of the method the flies use to bite.

The following are features of a horsefly bite:

The bite will be very painful because the horsefly does not release any anesthetic when it bites.
The fly makes a cut rather than a small puncture hole with mouthparts like a serrated saw.
The fly uses an anticoagulant to stop blood from clotting as it consumes it.
The fly anchors to the skin while drinking the blood with the help of small hooks along its mouthparts.
After a bite, the area around will be raised, and welts will develop.

The pain and welts can help identify horsefly bites.

The following may also occur:

a large, red, raised rash at the site or over a wider area
dizziness
weakness
wheezing
swelling and puffiness elsewhere in the body

Alone, a red, raised bump on the skin is not usually a sign of concern but if any of the above symptoms develop or if breathing becomes difficult, a person should seek medical attention as soon as possible. That person could be having a severe allergic reaction.

The bite can take time to heal, and an infection may develop. If pus or other signs of infection appear, the person should seek medical advice.

What do horseflies look like?

Horseflies have the following appearance:

They are large, often 2/3-inch in length.
They are dark in color and have striped chests and black bellies.
They have large, compound eyes.

Is a horsefly bite dangerous?

Horsefly bites can be very painful, but are not usually harmful to humans. However, there have been some cases of horseflies passing on tularemia — also known as rabbit fever — to humans.

Tularemia is a bacterial infection with a range of possible signs and symptoms. It can be life threatening but is treatable with antibiotics.

However, a person should seek medical help if:

there are signs of an allergic reaction or anaphylaxis
symptoms are severe and persistent
an infection develops at the site of the wound and discharges pus

Symptoms of serious horsefly reactions

A horsefly bite will cause:

pain
swelling in the area
lighter skin will become red, and darker skin tones may become darker
in some cases, dizziness, wheezing, and puffiness around the eye and lips due to an allergic reaction

Some people may have a more severe allergic reaction, or anaphylaxis, including:

tongue and throat swelling
swollen face, lips, hands, or feet away from the site of the bite
nausea, vomiting, or diarrhea
feeling very unwell
difficulty swallowing
dizziness
wheezing and breathing problems
puffiness around the eyes and lips

This is an emergency, and the person will need urgent medical attention.

Anaphylaxis: Symptoms and what to do

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

hives
swelling of the face or mouth
wheezing
fast, shallow breathing
a fast heart rate
clammy skin
anxiety or confusion
dizziness
vomiting
blue or white lips
fainting or loss of consciousness

If someone has these symptoms:

Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
Dial 911 or the number of the nearest emergency department.
Assist the person in moving from a sitting position to lying down. If they have vomited, turn them onto their side.
Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5 to 15 minutes, or they come back, use a second pen if the person has one.

Treatment for horsefly bites

Treating a horsefly bite is similar to treating other types of insect bites.

Tips for treating the symptoms of a horsefly bite are:

Clean the area with soap and plain warm water using a clean cloth or cotton wool.
Apply a cold compress or ice pack wrapped in a cloth to ease the pain and reduce swelling.
Use acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) to ease pain.
Take oral antihistamines to reduce itching.

A person should avoid scratching the wound, as this will likely worsen it and increase the risk of infection. Vinegar and baking soda are unlikely to help.

If a horsefly bite does become infected, the person should speak with a doctor. They may prescribe antibiotics.

Horseflies do not leave behind any mouthpart or stinger when they bite.

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How to prevent horsefly bites

Horseflies can be difficult to avoid in the summer, as their habitats are widespread.

There are some practical steps, however, that can help reduce the risk of horsefly bites:

Keep the skin covered with shoes, long pants, and long-sleeved tops.
Wear clothes that are light in color.
Wear loose clothing, as horseflies can bite through fabric.
Avoid perfumed cosmetic products, as these may attract flies.
Stay away from water in the summer, where horseflies breed.
Using insect repellent may deter flies but probably not prevent horsefly bites, though it is helpful against mosquitos that may be present in the same areas. The most effective repellents have 50% DEET.
Hang fly tape around buildings where animals live, such as a barn.

Frequently asked questions

What happens when a horsefly bites you?

Female horseflies bite when they need blood to develop their eggs. They use saw-like mouthpieces to cut through the skin. The bite can be very painful.

What does a horsefly bite look like?

When a horsefly bites a person, there will likely be pain and swelling in the area of the bite. If swelling occurs in other parts of the body or a person starts to have difficulty breathing, this may be a sign of an allergic reaction that needs emergency medical help.

What can you do for a horsefly bite?

A person should wash the area thoroughly with soap and water and avoid scratching it. Applying ice or a cold pack wrapped in a cloth can help ease pain and swelling. Over-the-counter pain relievers can also help with pain, and oral antihistamines may reduce itching.

Summary

Horseflies are large flies that usually bite cows and horses but can also bite humans. They have a very painful bite, as their mouthpieces cut into the skin. Only the females bite, and they do this to obtain blood to help develop their fertilized eggs.

As well as a painful bite, there may be large welts and swelling around the area. A horsefly bite is not usually dangerous, but some people can have an extreme allergic reaction or anaphylaxis. Anyone with symptoms of swelling or difficulty breathing after a bite needs emergency medical help.

A horsefly bite can take time to heal. While healing, it is essential not to scratch it, as it may become infected. Home and over-the-counter remedies can help manage pain and itching.

Allergy
Bites and Stings
Dermatology
Veterinary

How we reviewed this article:

SourcesMedical News Today has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Davis, J. (n.d.). Are horsefly bites on the rise?https://www.nhm.ac.uk/discover/news/2018/july/are-horsefly-bites-on-the-rise.html
Drago F, et al. (2018). Case report: Atypical cutaneous manifestations of tularemia after horsefly bite.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6086196/
Powers J, et al. (2023). Insect bites.https://www.ncbi.nlm.nih.gov/books/NBK537235/
Tularemia. (2024).https://www.cdc.gov/tularemia/index.html

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Medically reviewed by Helen Chen MCMSc, PA-C — Written by Markus MacGill — Updated on May 1, 2025

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