Can Flies Bite?

Yes, some flies can bite, but it depends on the species:

Biting Flies

Horse flies and Deer flies (family Tabanidae): Bite humans and animals. These flies have sharp mouthparts designed to cut skin and feed on blood. Horse fly bites and deer fly bites are often painful and can cause swelling, itching, or allergic reactions. They can also transmit animal pathogens.
Black flies (Simuliidae): Blood-feeding species exist. Female black flies bite to get protein for egg development. Their bites can be itchy, irritating, and occasionally lead to allergic reactions or transmit certain diseases like river blindness in endemic areas.
Biting midges (“no-see-ums,” family Ceratopogonidae): Tiny flies that bite humans and animals. Midge bites are irritating and often cause itchy red bumps.
Stable flies (Stomoxys calcitrans): Blood-feeding flies that resemble houseflies. They bite livestock and humans, causing painful lesions, irritation, and stress to animals.

Non-Biting Flies

House flies (Musca domestica): Do not bite. They feed on liquids and soft matter using sponging mouthparts. They can, however, transfer pathogens because they land on food and wounds.

Most common household flies (flesh flies, blowflies) do not bite humans, though some may feed on open wounds or decaying matter.

Only certain species have evolved to bite for blood meals. Most flies, including the common housefly, do not bite, but all flies can be a nuisance or a vector for disease.

Do Flies Bite?

Flies that bite—like horse flies, deer flies, black flies, stable flies, and sand flies—tend to bite under very specific conditions. Understanding these situations can help you avoid them or reduce the risk of bites:

Warm weather and sunny days – Many biting flies are most active in warm temperatures, often in late spring through early fall. Horse flies and deer flies, for example, hunt in bright sunlight.
Near water or damp areas – Black flies, sand flies, and some midges breed in or near rivers, streams, ponds, or marshy areas. Being near these habitats increases the risk of bites.
Outdoor activity – People spending time outdoors, especially walking, hiking, cycling, or working in fields or near forests, are more exposed. Movement attracts biting flies because they detect motion and carbon dioxide from breath.
Around animals – Stable flies, horse flies, and deer flies often bite livestock, pets, and humans nearby. They are drawn to body heat, sweat, and carbon dioxide.
Early morning or late afternoon – Some species, like deer flies, are most active during these cooler periods, though others, like horse flies, prefer midday sun.
Areas with exposed skin – Flies are more likely to bite where skin is uncovered, especially the arms, legs, neck, and face.

Some biting flies, like horse flies, prefer moving targets for easier detection, while black flies can bite even stationary individuals in large swarms.

Fly Bites

Fly bites themselves usually pose more of a nuisance than a direct health threat for humans, but certain species can carry specific risks:

Pain and irritation: Bites from horseflies, deer flies, black flies, biting midges, and stable flies are often painful or itchy. Repeated bites can lead to localized swelling, redness, and discomfort.
Allergic reactions: Some individuals may experience moderate to severe allergic responses. Symptoms can include swelling beyond the bite area, intense itching, hives, or, rarely, systemic reactions like anaphylaxis.
Infection at the bite site: Scratching can introduce bacteria, causing secondary skin infections such as cellulitis. Fly bites in livestock can lead to wounds that get infected, especially in hot or humid environments.
Transmission of pathogens: Certain biting flies are vectors for diseases. Black flies can transmit Onchocerca volvulus (river blindness) in endemic regions. Horseflies and deer flies can mechanically transfer animal pathogens like anthrax or equine infectious anemia. Stable flies can transmit diseases to livestock, though human transmission is rare. Most fly species do not transmit diseases directly through bites, but their feeding can carry microbes mechanically.
Psychological and productivity impacts: Bites can lead to sleep disturbances, stress, and reduced outdoor activity. In livestock or pets, persistent biting flies can reduce feeding efficiency, growth, or milk production.
Eye and mucous membrane irritation: Biting flies sometimes target the eyes, nose, or lips, causing conjunctivitis or irritation. Certain species, like the black fly, are notorious for attacking around the eyes in large swarms.

For humans, the main risks are pain, itching, allergic reactions, and occasional infection. The risk of serious disease transmission is largely geographically and species dependent, but bites can be a significant concern for livestock and pets.

Do Fly Bites Hurt?

Yes, whether a fly bite hurts depends on the species and its feeding mechanism:

Horseflies and deer flies: Bites are very painful. They have sharp, scissor-like mouthparts that cut the skin to access blood. The pain is often immediate and can be followed by swelling and redness.
Stable flies: Painful bites, though usually less severe than horseflies. They pierce the skin and suck blood, leaving a stinging sensation.
Black flies: Bites can be painful, often described as sharp or burning. Females need blood for egg development, and swarms can produce multiple painful bites.
Biting midges (“no-see-ums”): Bites are itchy more than painful, but can feel like tiny pinpricks. Multiple bites can cause significant irritation.

Painful bites are primarily associated with horseflies, deer flies, black flies, and stable flies. Tiny biting flies like midges are more itchy than painful, but multiple bites can still be very uncomfortable.

Do Fly Bites Itch?

Yes, many fly bites do itch, but the intensity and timing depend on the species and the person’s sensitivity:

Horsefly and deer fly bites: Pain first, then itching: These bites are immediately painful due to the cutting action of their mouthparts. Itching develops later, often lasting several hours to a few days.
Stable fly bites: Moderate itching is common, sometimes accompanied by mild pain.
Black fly bites: Intense itching is characteristic.
Biting midges (“no-see-ums”): Highly itchy, often more irritating than painful.

What Do Fly Bites Look Like?

Fly bites vary in appearance depending on the species, number of bites, and the individual victim’s reaction:

Horsefly and deer fly bites: Red, swollen welts with a puncture mark in the center. Often ½–1 inch in diameter, sometimes larger if allergic reaction occurs. Can bleed slightly at first; pain is immediate.
Stable fly bites: Small to medium red bumps, sometimes with a central puncture. Itching and mild swelling; usually less severe than horsefly bites.
Black fly bites: Small red bumps, often in clusters or lines where multiple flies have fed. Swelling, itching, and sometimes a burning sensation; multiple bites can create a patchy rash-like area.
Biting midge (“no-see-um”) bites: Tiny red dots, often with a slight raised center. Very itchy; multiple bites can form clusters resembling a rash.
Secondary effects: Scratching bites can lead to redness, scabs, or secondary infection. In sensitive individuals, bites may form blisters or large welts.

Painful bites (horseflies, deer flies, stable flies) often produce large, red, raised welts. Small biting flies (black flies, midges) create clusters of tiny itchy red bumps. Non-biting flies leave no direct bite marks, but can still contaminate skin or wounds.

Do Fly Bites Bleed?

Whether a fly bite bleeds depends on the species and the way it feeds:

Horseflies and deer flies: Yes, they can bleed. Their mouthparts cut the skin to access blood, often leaving a small wound that can ooze for a few minutes.
Stable flies: Occasionally bleed. They pierce the skin to feed, but usually only a tiny drop of blood appears.
Black flies: Rarely bleed noticeably. They scrape the skin slightly to feed, which can sometimes leave tiny spots of blood. Multiple bites may create a patchy red area.
Biting midges (“no-see-ums”): Unlikely to bleed. Their bites are tiny punctures that rarely cause visible blood.

Do Fly Bites Swell?

Yes, fly bites often swell, but the degree and duration depend on the species, the bite’s severity, and the individual’s reaction:

Horseflies and Deer flies: Swelling is common and often pronounced. Their bites cut the skin to access blood, causing large, red, raised welts that can remain swollen for hours to days. Pain and itching usually accompany the swelling.
Stable flies: Moderate swelling is typical. Bites usually produce small red bumps that may be tender and itchy.
Black flies: Swelling varies depending on the number of bites. Single bites may cause minor swelling, but multiple bites in a cluster can create a patchy, raised area. Intense itching often worsens the swelling.
Biting midges (“no-see-ums”): Minimal to moderate swelling. Bites are tiny but can appear in clusters, producing localized raised bumps.

What To Do About Fly Bites

Clean the bite immediately: Wash the area with soap and cool water to remove dirt and reduce the chance of infection. Gently pat dry with a clean towel—avoid rubbing.
Stop any bleeding: If the bite is bleeding (common with horseflies and deer flies), apply gentle pressure with a clean cloth or gauzefor a few minutes until it stops.
Reduce pain and swelling: Apply a cold compress or ice pack for 5–10 minutes to relieve pain and limit swelling. Over-the-counter pain relievers (acetaminophen or ibuprofen) can be used if necessary.
Manage itching: Apply anti-itch creams or gels containing hydrocortisone or calamine lotion. Oral antihistamines (e.g., cetirizine, loratadine) can help with more severe itching or allergic reactions. Avoid scratching, as this can lead to infection or scarring.
Watch for infection or allergic reactions: Signs of infection: Increasing redness, warmth, swelling, pus, or pain. Signs of allergic reaction: Hives, widespread swelling, difficulty breathing, dizziness—seek emergency medical care immediately if these occur.
Promote healing: Keep the bite clean and dry. Cover with a light bandage if you’ll be outdoors or if scratching is likely. Most bites heal within a few days to a week; persistent swelling or unusual symptoms should be checked by a doctor.

To reduce the chances of getting bitten by flies in the future, wear long sleeves, pants, and insect repellent when in fly-prone areas. Use fly screens, nets, or traps indoors and around livestock areas. Contact our team of exterminators for professional fly control.