The Pesky Black Flies: What Makes Them So Annoying? April 28 2023

Black flies, also called buffalo gnats, are small, dark-colored insects that belong to the family Simuliidae. These pesky insects are found in almost every part of the world, especially in areas with running water. Black flies are known for their painful bites, which can leave you with red, swollen, and itchy welts. 

Anatomy of Black Flies

Black flies are small, measuring between 1.5 and 5 mm in length, and are usually black or dark grey in color. They have a humpbacked appearance, with a broad head and a pair of large eyes that are dark in color. Black flies have six legs and two wings, which they use to fly and hover around their prey. These insects are known for their sharp, piercing mouthparts that they use to suck blood from their hosts.

Habitat and Distribution

Black flies are found in almost every part of the world, especially in areas with running water, such as rivers, streams, and lakes. They prefer clean, unpolluted water, where they lay their eggs. 

Why Are Black Flies So Pesky?

Biting Behavior

Black flies are notorious for their painful bites, which can leave you with red, swollen, and itchy welts. These insects are attracted to the carbon dioxide we exhale and the scent of our sweat and body heat. Once they detect their prey, they fly in swarms and land on exposed skin, such as the face, neck, and arms, and bite through the skin to suck blood.

Breeding Habits

Black flies have a unique breeding habit that contributes to their peskiness. Female black flies lay their eggs on the surface of running water, where they hatch into larvae. The larvae attach themselves to rocks or other underwater structures and feed on algae and other organic matter. After several weeks, the larvae pupate and emerge from the water as adult flies. This cycle repeats throughout the year, with black flies constantly breeding and producing new generations.

Short Lifespan

Black flies have a short lifespan, with adult flies living for only a few weeks. This means that they have a limited time to mate and reproduce, which results in a high population density during their active season. The high population density, coupled with their biting behavior, makes black flies a significant nuisance to humans and animals alike.

Allergic Reactions

Some people may develop an allergic reaction to black fly bites, which can cause severe itching, redness, and swelling. In rare cases, black fly bites can lead to anaphylaxis, a life-threatening allergic reaction. People should seek medical attention immediately if they experience difficulty breathing, rapid heartbeat, or swelling of the face or throat.

Preventing Black Fly Bites

Preventing black fly bites is essential, especially if you live in an area with high black fly activity. Here are some tips to help you avoid getting bitten by black flies:

Use Insect Repellent

Insect repellents, such as DEET or picaridin, can help repel black flies and other biting insects. Be sure to follow the instructions on the label and apply the repellent to all exposed skin.

Avoid Peak Activity Times

Black flies are most active during the early morning and late afternoon, so it is best to avoid outdoor activities during these times.

Stay Indoors

If black flies are particularly bad in your area, it may be best to stay indoors during their active season.

Use Protective Screens

Installing screens on your doors and windows can help keep black flies and other biting insects out of your home.


Black flies are pesky insects that can be a significant nuisance to humans and animals alike. Their biting behavior, breeding habits, short lifespan, and potential for allergic reactions make them a considerable concern for those who live in areas with high black fly activity. By taking preventative measures, you can avoid getting bitten by black flies and enjoy your time outdoors.

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