While many flies are perceived as harmless nuisances, some species are equipped to bite humans. Not all flies possess biting mouthparts, but a distinct group does, and their bites can be quite painful. Understanding which flies bite and their feeding behavior is helpful for protection outdoors.
Flies That Bite Humans
Several types of flies are known to bite humans, each with distinct characteristics. Horse flies (Tabanidae) are relatively large, stout-bodied insects, often identified by their metallic or iridescent eyes, and can inflict a painful bite. Deer flies (Chrysops), which are smaller than horse flies, typically have dark bands on their wings and often appear in wooded areas near water. Stable flies (Stomoxys calcitrans) closely resemble common house flies but can be distinguished by their pointed, piercing mouthpart that protrudes forward, and they frequently bite ankles and legs.
Black flies (Simuliidae), also known as buffalo gnats, are small, hump-backed insects found near flowing water. Their bites can cause bleeding, itching, and swelling. Sand flies (Phlebotominae) are tiny, hairy, moth-like flies most active during dusk and dawn, and their bites typically result in small, itchy red bumps.
Why and How Flies Bite
Only female flies bite, as they require a blood meal for egg development and production. Without this protein source, they cannot complete their reproductive cycle. Male flies, in contrast, typically feed on nectar and plant sugars.
Biting mechanisms vary significantly among species, depending on their specialized mouthparts. Some flies, like stable flies, possess piercing-sucking mouthparts, using a needle-like proboscis to access a blood vessel. Other flies, such as horse flies and deer flies, utilize cutting-sponging mouthparts. These mouthparts slice the skin, creating a wound for blood pooling, which a sponge-like labellum then soaks up. During biting, flies often inject saliva containing anticoagulants to prevent clotting, ensuring continuous feeding.
Understanding and Preventing Bites
Fly bites often result in immediate, localized reactions, including pain, itching, redness, and swelling around the bite site. The intensity of these symptoms can vary depending on the fly species and an individual’s sensitivity. In some instances, scratching the itchy bites can break the skin, potentially leading to secondary bacterial infections. While most fly bites are not serious, some species can transmit pathogens, though this is less common in many regions.
Preventing fly bites involves several strategies. Wearing protective clothing, such as long-sleeved shirts and pants, provides a physical barrier. Light-colored clothing may also be less attractive to some biting flies. Applying insect repellents containing DEET or picaridin to exposed skin provides an effective deterrent. Avoiding outdoor activities during peak fly activity times, like dawn and dusk or in swampy areas, can also reduce exposure.