Black Fly Bites (Buffalo Gnats): What They Look Like and How to Find Relief

Black flies are small insects closely related to mosquitoes that bite and suck the blood of livestock and humans. The bites can be painful and long-lasting.

Black flies are also called “buffalo gnats,” because they have a small hump behind their head, similar to a bison or buffalo. They usually hatch near flowing water in late spring and early summer and can swarm in large numbers. They are found in most of the United States but are more common in the upper Midwest and Northeast.

What Do Black Fly Bites Look Like?

A black fly bite looks like a mosquito bite, appearing as a small bump on the skin that may be inflamed. You may be able to see the hole where it punctured your skin to feed on blood.

Only the females bite. You may not feel it initially because the flies inject a numbing substance into your skin. Black flies often attack your head or face but can bite you anywhere.

The bites can become painful and itchy and may swell or lead to blisters. The symptoms are a reaction to the insect’s saliva, which contains toxins and substances that prevent your blood from clotting quickly so the insect can feed.

Other Common Symptoms

Sometimes, black fly bites can cause what’s known as “black fly fever,” though technically, the insects do not infect humans with diseases. Still, symptoms can include:

• Burning sensation or soreness at the site of the bite
• Headache
• Numbness
• Low fever
• Nausea
• Swollen lymph nodes

Black fly bite symptoms can last for many days.

Late complications of black fly bites include persistent eruptions that can last from three to 16 months. These can show various types of skin disorders, including erythematous (red or discolored) and edematous (swelling) reactions, persisting for weeks or months.

When to Contact a Healthcare Provider

It’s not common, but some people may have a severe allergic reaction to black fly bites due to the substances the flies inject into the skin. In very rare cases, many bites at one time could be life-threatening.

If you have any trouble breathing or feel faint after being bitten by black flies, seek emergency treatment.

If you see signs of infection, such as increased pain, redness or discoloration, warmth, or pus, that’s also a sign to contact a healthcare provider.

How to Find Relief at Home

If you see black fly bites on your skin, you can take the following steps to treat them:

• Clean and disinfect the area to reduce the chance of infection.
• Use a topical anti-itch or pain-reducing product such as cortisone cream or spray.
• Apply a cool compress to the area for 10 to 15 minutes at a time. A cloth soaked in ice water or wrapped around an ice bag may be used. Don’t put ice directly on your skin.
• If necessary, take an over-the-counter (OTC) pain medication such as Advil or Motrin (ibuprofen).
• Avoid scratching, which can wound the skin further and possibly lead to infection.

Ways to Prevent Bites

It’s hard to repel black flies because they can appear in such large numbers. They may fly around your head, into your eyes or ears, or get in your hair. However, you can take steps you can take to avoid bites, including:

• Avoid daytime exposure: Black flies feed in the daytime, so avoid being outdoors during the day if black flies are hatching or swarming.
• Avoid sources of running water: The flies hatch in or near flowing or running water, so avoid streams and other running water sources.
• Wear light-colored clothing: Black flies are attracted to dark colors.
• Cover up: Wear long sleeves, long pants, and a hat. Wear clothes that fit close to your body because the flies can crawl under loose sleeves or into boots or shoes.
• Consider wearing a head net: To protect your face and neck when you can’t avoid areas with swarms, wear a head net to keep out mosquitoes and gnats.
• Use repellents: DEET (N,N-diethyl-meta-toluamide), picaridin, and oil of lemon eucalyptus (OLE) will help. However, do not use these ingredients on children under 3 years of age.

Summary

Black flies are small insects with a big bite. They hatch near flowing water in late spring and early summer in the U.S. Midwest and Northeast and can appear in swarms.

To prevent the bites, which can be painful and last a long time, avoid areas where they are hatching or wear long-sleeved shirts and long pants, plus a hat. Consider using insect repellent, though the insects will fly around your eyes, face, and hair. A head net may be useful in areas with swarms.

Treat bites with topical anti-itch and pain spray or a cold compress. Contact your healthcare provider if you feel faint or see signs of infection.