While many common flies, such as the house fly, are often perceived as nuisance insects incapable of biting humans, this is a misconception. Many fly species do bite, and their bites can range from mildly irritating to quite painful. Understanding which flies bite and how they interact with humans can help minimize uncomfortable encounters and manage symptoms. Some biting flies can also transmit pathogens, making awareness important for health.
Flies That Bite
Several fly types bite humans, differing significantly from non-biting species like house flies that primarily feed on liquids using sponging mouthparts. Stable flies resemble house flies but deliver painful bites, often targeting human feet and ankles, though they typically bite cattle and horses.
Larger biting flies include aggressive horse flies, up to 1.25 inches long, found near water or warm, wet environments. Deer flies, smaller than horse flies but larger than house flies, have distinct dark wing bands and are prevalent in wooded or wetland areas.
Other biting species include black flies, or buffalo gnats, which are small and humpbacked. Biting midges, or “no-see-ums,” are tiny (less than 1/8 inch) but deliver painful bites, often found near coastal or marshy areas. Sand flies, also small, are typically found in tropical and subtropical regions.
Why and How Flies Bite
Female flies bite humans and other mammals to obtain a blood meal, crucial for their reproductive cycle. Blood proteins and nutrients are necessary for egg development. Male flies of these species do not bite, instead feeding on nectar or plant fluids.
Biting flies have specialized mouthparts, unlike non-biting flies, allowing them to pierce skin and access blood vessels. Horse flies and deer flies use scissor-like mouthparts to cut skin, creating a wound from which they lap up pooling blood. Other flies, like stable flies, have a piercing proboscis. During biting, flies often inject saliva containing anticoagulants, preventing blood clotting and ensuring continuous flow for feeding.
Recognizing and Responding to Bites
Biting fly encounters often cause immediate pain, followed by symptoms at the bite site. Common reactions include redness, swelling, and intense itching. Bite appearance varies; some cause small red bumps, while others, like horse fly bites, result in raised, discolored welts or minor bleeding. Deer fly bites can also be painful, leaving red bumps or blisters.
To manage discomfort, clean the bite area with soap and water to reduce infection risk. Apply a cold compress or ice pack for 10 to 20 minutes to alleviate swelling and pain. Over-the-counter anti-itch creams with hydrocortisone or oral antihistamines can relieve itching and inflammation.
Most fly bites are not serious and resolve within days. However, monitor the bite area for infection signs like increasing redness, warmth, pus, or fever. In rare instances, individuals may experience severe allergic reactions (anaphylaxis), characterized by dizziness, weakness, difficulty breathing, facial or throat swelling, or spreading hives. Such symptoms warrant immediate medical attention.
Minimizing Exposure to Biting Flies
Using insect repellents with active ingredients such as DEET or picaridin can deter various biting insects. Always follow the product’s instructions for safe and effective application. Treating clothing with permethrin, a different type of repellent, can also offer protection, but this chemical should never be applied directly to the skin.
Wearing protective clothing, particularly in areas where biting flies are prevalent, creates a physical barrier against bites. Long-sleeved shirts, long pants, and hats can reduce exposed skin. Light-colored clothing may also be less attractive to some biting flies, such as horse flies, which are drawn to large, dark objects.
Being aware of the peak activity times and habitats of biting flies can further minimize exposure. Many biting flies, including deer flies and biting midges, are most active during daylight hours, especially at dawn and dusk, or in warm, humid conditions. Avoiding outdoor activities during these times or in known fly hotspots, such as marshy areas or dense woods, can be beneficial. Additionally, ensuring windows and doors have well-maintained screens can prevent flies from entering indoor spaces. Tightly woven mesh screens, sometimes referred to as “no-see-um” screens, can be particularly effective against smaller biting midges.