Horseflies are a type of flying insect, and their bites can be painful. In rare cases, some people develop serious allergies to horsefly bites.

Avoiding horseflies outdoors in summer can be difficult, but dealing with their bites is usually simple.

Because of the way they inflict damage, horsefly bites can be more painful than bites from other bugs.

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

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A horsefly bite can be extremely painful.

Treating a horsefly bite is similar to remedies for other types of insect bite.

The main precaution for treating horsefly bites is to be wary of infection. Horsefly bites may be more likely to become infected than other insect bites because of the way that horseflies damage the skin.

If a horsefly bite does become infected, visit a doctor. They may prescribe antibiotics.

    For any horsefly bite, home care includes:

    • not scratching the wound, as this is likely to make it worse and increase the risk of infection
    • cleaning the bitten skin with soap and plain warm water using a clean cloth or cotton wool
    • easing the pain and reducing swelling with a cold compress or ice pack held over the bite for 10 minutes
    • not using any other remedies aside from plain water and soap

    Vinegar and bicarbonate of soda are unlikely to help.

    The horsefly will also not leave behind any mouthpart or stinger when they bite people.

    When to call a doctor

    A person will not need medical attention unless infection occurs in the wound. In the rare cases of a severe allergy soon after a bite, people should call for an ambulance.

    Horsefly bites are particularly painful and slow to heal compared to other insect bites. This is because of the method that the flies use to bite.

    The following are characteristic of a horsefly bite:

    • It is a cut rather than a small puncture hole.
    • The mouthparts of the horsefly use a scissor-like action to create a wound in the skin.
    • The fly “mops up” the blood after cutting through the skin.
    • The fly anchors to the skin while drinking the blood with the help of small hooks along its mouthparts.

    The bite in the skin itself is usually red and surrounded by a raised area of skin, called a weal or hive.

    The pain, redness, and weal help to identify horsefly bites.

    People should watch out for spreading redness of the skin, as well as the presence of pus or other discharge coming from the wound. Increased pain and swelling might also signal an infection. If a bite becomes infected, it does not happen immediately but usually at least a day or two later.

    Horseflies are not usually harmful to humans. They do not transmit any disease apart from swamp fever, which can be fatal in horses.

    Symptoms of serious horsefly reactions

    A serious allergy to horsefly bites is not common, but may cause extra symptoms, such as:

    • dizziness
    • wheezing
    • temporarily swollen skin, for example around the eye and lips

    A more severe allergic reaction, or anaphylaxis, is rare but an emergency. People should call for an ambulance for any signs of 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 or breathing

    People who demonstrate a severe allergy to horseflies will usually have had a horsefly bite in the past. The immune system then adapts to protect the individual against any further instances but is oversensitive to future bites.

    People who have severe allergies may need to carry an emergency epinephrine injection for the treatment of future bite reactions.

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    Horseflies are biologically fine-tuned to bite larger animals.

    A horsefly is a flying insect found most often in rural, farmland areas, where they feed on large mammals. They occur across North America.

    They can also be found in urban areas near water-rich breeding sites, such as a lake.

    There are numerous species of horsefly, including flies known as “clegs.”

    Horseflies must bite large animals, including horses, cattle, dogs, and humans, as part of their life cycle.

    Only female horseflies bite, as males do not have the appropriate mouthparts. Females need to drink blood to support egg production.

    Female horseflies need up to 0.5 milliliters (ml) of blood for reproduction, which is a large amount when compared to their size. They can take up an estimated 200 milligrams (mg) of blood in a few minutes.

    This process is similar in some ways to that of other blood-sucking arthropods, such as ticks and mosquitos.

    The horsefly is specially adapted to consume as much blood as possible. It releases substances that stop blood clotting at the point of skin puncture. Traditional Chinese medicine has even used horseflies for these anti-clotting characteristics.

    Horseflies are more prevalent during hot, sunny weather with low wind, such as during daytime in the middle of summer. They can become more of a pest when thunder accompanies hot weather.

    What do horseflies look like?

    Horseflies have the following appearance:

    • They are large.
    • Their coloring is dark, and they have striped chests and black bellies.
    • They have large, compound eyes.

    Horseflies are difficult to avoid in the summer, as their habitats are widespread. There are some practical steps, however, that a person can take to reduce the risk of horsefly bites:

    • Keep skin covered with shoes, long pants, and long-sleeved tops that are light in color.
    • Avoid walking in long grass.
    • Avoid perfumed cosmetic products, as these may attract flies.
    • Staying away from water in summer, where horseflies breed.
    • Using insect repellent will probably not prevent horsefly bites, though it is helpful against mosquitos which may be present in the same areas. The most effective repellents have 50 percent diethyltoluamide (DEET).