Black flies, belonging to the family Simuliidae, are small, humpbacked insects sometimes known as buffalo gnats. Unlike mosquitoes that pierce the skin, the female black fly uses specialized, blade-like mouthparts to cut a small hole in the skin. This “slice-and-suck” mechanism causes blood to collect in the wound, which the fly then consumes. The resulting reaction is often more distinct and severe than a typical mosquito bite due to this abrasive feeding style and the substances injected.
Visual Appearance of the Black Fly Bite
Immediately after a black fly feeds, the bite presents as a small, distinct, lacerated puncture at the center of the affected area. This central hole is a key identifying feature, contrasting sharply with the simple, smooth puncture left by a mosquito. Initial bleeding or oozing is common due to the fly injecting salivary anticoagulants and toxins, which prevent the blood from clotting while the insect feeds.
The body’s reaction to the injected saliva quickly produces a localized, raised welt called an erythematous wheal. This swelling (edema) can be firm and significantly pronounced, sometimes reaching the size of a small coin or larger. The area is typically surrounded by intense redness, often making the bite resemble a small bruise or a fluid-filled blister.
Black flies are highly attracted to exposed skin, carbon dioxide, and movement, frequently attacking the neck, scalp, ears, and ankles. Because they often fly in swarms, a person may sustain multiple bites in a concentrated area. The resulting cluster of inflamed, reddened welts can make the area look significantly irritated.
Associated Symptoms and Severe Reactions
The discomfort associated with a black fly bite often involves intense, prolonged itching known as pruritus. A localized burning sensation or pain at the site is also a common initial symptom, frequently described as more irritating than a mosquito bite. These symptoms are the body’s allergic response to the foreign proteins and toxins contained within the fly’s saliva.
Persistent scratching of the open puncture wound can lead to secondary bacterial infection. Signs of this complication include increased warmth, spreading redness, worsening pain, and the presence of pus.
This systemic response, known as Simuliotoxicosis or “Black Fly Fever,” is marked by general symptoms such as headache, nausea, low-grade fever, and swelling in the lymph nodes near the affected area. Signs of a severe allergic reaction include excessive swelling of the face, tongue, or throat, or difficulty breathing. These reactions, though rare, warrant immediate medical attention as they can lead to anaphylaxis.
Immediate Care and Relief Measures
The first step in treating a black fly bite is to minimize the risk of secondary infection by cleaning the wound thoroughly. Wash the affected skin gently with mild soap and water to remove any residual saliva or environmental contaminants. Avoiding the urge to scratch the bite is important, as this prevents further trauma to the skin barrier.
To help reduce the localized swelling and inflammation, apply a cool compress or an ice pack wrapped in a cloth to the area for 10 to 15 minutes at a time. For relief from persistent itching, over-the-counter topical treatments such as hydrocortisone cream or calamine lotion can be applied directly to the welt. Oral antihistamines can also be taken to help subdue the body’s overall allergic response and reduce the intensity of the pruritus.
Medical attention is necessary if you observe signs of a worsening infection, such as pus or streaks of redness spreading from the bite. Seek emergency care immediately if you experience any symptoms of a severe allergic reaction, including lightheadedness, facial swelling, or trouble breathing. A healthcare provider should also be consulted if the systemic symptoms of Black Fly Fever, such as fever and nausea, persist or worsen.