Can Flies Bite?

Yes, some flies can bite, but it depends on the species. Most common house flies do not bite—they feed on liquids and decaying matter. However, several types of flies are blood-feeders and can bite humans and animals:

Horse flies and deer flies – These flies have sharp mouthparts that cut the skin and feed on blood. Their bites are painful, can cause swelling, and sometimes lead to allergic reactions. They are most active in warm, sunny conditions near water or wooded areas.
Black flies – These small flies also feed on blood and can deliver painful bites. They are especially common near rivers and streams.
Sand flies – Found in tropical and subtropical regions, sand flies bite and can transmit diseases such as leishmaniasis.
Stable flies – Often mistaken for house flies, they bite livestock and occasionally humans. Their bites can be itchy and irritating.
Biting midges (no-see-ums) – Tiny flies that bite exposed skin, leaving small itchy red bumps.

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.
Stillness vs. movement – 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

Biting flies pose several risks, ranging from mild irritation to serious health concerns. The level of risk depends on the species, the bite location, and the person’s sensitivity. Here’s a detailed breakdown:

Localized Reactions

Pain and irritation: Biting flies such as horse flies, deer flies, and stable flies have sharp mouthparts that cut the skin, causing immediate pain.
Redness, swelling, and itching: Most bites trigger inflammation as the body reacts to saliva injected during feeding.
Small welts or blisters: Some people develop raised bumps or even tiny blisters at the bite site.
Secondary infection: Scratching bites can break the skin and introduce bacteria, leading to infections like cellulitis.

Allergic Reactions

Mild allergic reactions: Swelling beyond the bite site or increased redness.
Severe reactions (rare): Individuals with strong sensitivity could develop systemic reactions, such as hives or even anaphylaxis in extreme cases.

Disease Transmission

Some biting flies are vectors for pathogens that affect humans and animals:

Horse flies and deer flies: Can mechanically transmit bacteria or viruses between hosts, including tularemia (a rare bacterial infection).
Black flies: Can transmit Onchocerca volvulus, causing river blindness in endemic regions.
Sand flies: Known carriers of Leishmania parasites, causing leishmaniasis.
Stable flies and other blood-feeding species: Can transmit animal diseases, which indirectly affect humans working with livestock.

Discomfort and Behavioral Impacts

Persistent biting can make outdoor activities unbearable, interfere with work or recreation, and stress livestock or pets.
Swarming species (like black flies) can trigger panic responses or injuries as people try to swat them away.

Rare Complications

Secondary bacterial infections from scratching or poor hygiene.
Skin lesions in immunocompromised individuals, especially if bites are frequent or large.

Most fly bites cause temporary irritation, but in areas with disease-carrying species, bites can carry serious risks. Prevention with protective clothing, repellents, and habitat management is the most reliable strategy.

What Do Fly Bites Look Like?

Fly bites can vary depending on the species, the person’s reaction, and how recently the bite occurred:

General Appearance

Small red bumps: Most fly bites appear as tiny, round, reddish spots.
Raised welts or lumps: Horse fly, deer fly, and stable fly bites often form raised welts that can be painful.
Itchy or inflamed: The skin around the bite may swell and become itchy.
Clustered bites: Biting midges (no-see-ums) and black flies may leave multiple bites close together, sometimes forming a line.

Species-Specific Characteristics

Horse fly / Deer fly bites: Painful, sharp bite marks. Usually ½ to 1 inch in diameter, red and swollen. May bleed slightly immediately after the bite.
Black fly bites: Small red bumps, often in clusters. Can be intensely itchy. Often appear on exposed areas like arms, neck, and face.
Sand fly bites: Tiny red papules. Often grouped in clusters. Can blister or develop into pustules in sensitive individuals.
Stable fly bites: Similar to mosquito bites: small, red, itchy bumps. May occur on legs and ankles if around livestock.
Biting midges (no-see-ums): Pinprick-sized red spots. Often very itchy. Sometimes form a line of several bites.

Timing and Progression

Immediate: Pain, redness, and slight swelling at the bite site.
1–2 days: Itching may increase, bumps may grow slightly.
Several days: Most swelling and redness subside, though some people may have prolonged itching or secondary irritation from scratching.

Biting fly bites are usually raised, red, and sometimes clustered, and they often hurt immediately or become itchy quickly—unlike common house fly contact, which usually doesn’t break the skin.

What To Do About Fly Bites

If you get bitten by a fly, most bites are mild and can be treated at home, but taking the right steps helps prevent infection, reduce discomfort, and avoid complications:

Immediate Care

Clean the bite area: Wash with soap and cool running water to remove any bacteria or debris. Pat dry with a clean towel.
Stop any bleeding: If the bite has broken the skin, apply gentle pressure with a clean cloth or tissue.

Relieve Pain and Itching

Cold compress: Apply an ice pack or cold cloth for 10–15 minutes to reduce swelling and pain.
Topical treatments: Over-the-counter anti-itch creams, hydrocortisone, or calamine lotion can help with redness and itching.
Oral medications (if needed): Antihistamines like cetirizine or diphenhydramine can reduce itching and allergic reactions.

Prevent Infection

Avoid scratching, as this can break the skin and introduce bacteria.
Keep the area clean and monitor for signs of infection: increasing redness, warmth, swelling, pus, or pain.

Monitor for Allergic or Severe Reactions

Seek medical attention immediately if you notice:

Rapid swelling beyond the bite site
Difficulty breathing or swallowing
Dizziness, hives, or widespread rash

When to See a Doctor

Bite becomes infected (red, swollen, painful, or oozing).
Persistent or worsening swelling or itching after several days.
You develop a fever, malaise, or other systemic symptoms.
You were bitten in a region known for disease-carrying flies (e.g., sand flies transmitting leishmaniasis).

Prevention for the Future

Wear long sleeves, pants, and hats in fly-prone areas.
Use insect repellents containing DEET, picaridin, or oil of lemon eucalyptus.
Avoid areas near standing water or livestock during peak fly activity.
Install physical barriers (nets, screens) when possible.