May 27, 2025, 12:39 pm | Read time: 5 minutes
A black fly is tiny, but its bite is extremely painful. Scratching the wound can lead to serious consequences, potentially even life-threatening ones. Find out what you can do if bitten by this insect here.
There are mosquitoes that sting. And then there’s the black fly–it bites. A bite from a black fly is dangerous and can have serious consequences. Sometimes, the victim’s life is even at risk! Technically, it’s not a bite. The tiny insect, just a few millimeters in size, uses its saw-like and spreading tools to tear a crater in the human epidermis. The bloodsucker’s goal is to reach a vein. If the black fly hits a blood vessel, it sucks for a full two minutes. The insidious part: You don’t notice it at first because the wound is numbed.
Overview
What Is a Black Fly?
The black fly belongs to the Simuliidae family. It is two to six millimeters in size, dark, humped, and often referred to as a “flying tick” due to its stocky body and wing shape. Although it looks like a harmless fly, the females are active bloodsuckers. Black flies are now represented in Germany with around 57 species and originally migrated from Scandinavia. They prefer moist areas with flowing water, where they lay their eggs in the spring. Their larvae develop particularly well in warmth and high humidity—which is why hot summers promote their spread.1
The Bite Is Extremely Painful
But then! The perpetrator (it’s the females that suck blood) is long gone once the numbness wears off. And the ensuing pain is intense. It throbs, it presses, it pulls. The bite of a black fly is considered extremely unpleasant. A mere mosquito bite is nothing in comparison. Doctors even warn that a bite can have far-reaching consequences. It’s not uncommon to experience headaches, body aches, and shortness of breath.
How Do You Know You’ve Been Bitten?
The bite site usually appears as a small red dot surrounded by a painful swelling. The injected protein mixture numbs and inhibits blood clotting—hence the bite initially goes unnoticed. Subsequently, severe itching, prolonged skin irritation, and even hypersensitivity reactions can occur. In animals like cattle or dogs, inflammatory reactions are also possible.2
Does a Black Fly Bite Mean Life-Threatening Danger?
Black flies inject an anticoagulant substance into their victim’s wound. This can trigger an allergic reaction. As a result, redness, massive swelling, and wound infections occur. Pathogens can quickly enter through the open wound, potentially leading to blood poisoning. In the worst-case scenario, a black fly bite can even lead to circulatory failure and life-threatening danger, some doctors warn.
Whether a bite becomes life-threatening depends on several factors: the immune system’s response, wound care, and possible bacterial infections. Particularly with large swellings, fever, or shortness of breath, medical help should be sought immediately. People with known allergies or sensitive skin often react more strongly to the toxins involved.
What Helps Against the Bite?
Even though it’s difficult, don’t give in to the itching and scratch the wound! If possible, cool the wound with cold water or, better yet, ice. Your own saliva can also help disinfect the bite crater. In the post-COVID-19 era, many still carry disinfectants, which also help. Since black flies can transmit bacteria, health should be closely monitored. If symptoms like fever or persistent pain worsen, a doctor should be consulted as soon as possible. Pay particular attention to large swellings, as they indicate an allergic reaction, which can lead to cardiovascular problems.
Ointments and Gels
If available, apply an antihistamine gel to the wound. Dermatocorticoids and antibiotic-containing ointments are also helpful. Not only cold, but heat can also help. For example, using an electronic bite healer. The device generates short, tolerable heat on a small metal plate. This so-called heat pen is then pressed onto the wound. The heat neutralizes the toxins, and the itching noticeably subsides in no time. The coagulation of the toxins also prevents swelling of the wound.
Cleaning the Bite Site
Cleaning the bite site with soap and water is also important to prevent infection. Antihistamines—whether in tablet or cream form—can help with severe itching. In cases of particularly severe reactions or if symptoms persist for several days, medical advice should be sought.
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Avoiding Contact with Black Flies—But How?
Fortunately, black flies are not typically found indoors. The insects prefer wetlands and meadows, where they have their breeding grounds. Those who spend time there should wear long clothing and tuck socks over their pant legs. The insects cannot penetrate the fabric with their mouthparts. A mosquito repellent spray also helps. Those who are allergic or have sensitive skin should seek advice from a pharmacy.
Black flies are mainly active during the day, especially in sunny and calm weather. They pause their activity during rain or strong winds. It becomes particularly dangerous near still or slow-flowing waters. Those traveling there should wear light, long-sleeved clothing, and closed shoes. Insect repellents containing DEET or Icaridin offer additional protection. Windows with fine mesh screens keep the insects out of indoor spaces.3