Flies do not possess stingers and therefore cannot sting like bees or wasps. What people often experience as a “sting” from a fly is actually a bite, a mechanism some fly species use to feed.
Stings Versus Bites
The fundamental difference between a sting and a bite lies in the insect’s anatomy and purpose. Stinging insects, such as bees, wasps, and hornets, use a specialized organ called a stinger, typically located at the rear of their body, to inject venom. This action is primarily a defense mechanism or a way to immobilize prey. Flies, however, lack this barbed stinger and venom sac.
In contrast, biting insects utilize their mouthparts to break the skin, usually to obtain a blood meal. When a fly “bites,” it employs its unique mouthparts to penetrate the skin and, in some cases, inject saliva containing anticoagulants to facilitate blood flow. The discomfort and reactions experienced are due to this biting action and the substances injected, not a venomous sting.
How Flies Bite
Biting flies possess specialized mouthparts that enable them to cut or pierce the skin to access blood. Some flies, like horse flies and deer flies, have blade-like mouthparts that cut or slash the skin, creating an open wound from which they lap up blood. This method is often painful.
Other biting flies, such as stable flies, have a pointed proboscis that acts like a needle, piercing the skin. Once the skin is broken, these flies inject saliva containing anticoagulants to prevent blood clotting, allowing efficient feeding. Female flies across many biting species require blood meals for egg development and reproduction.
Common Biting Flies
Several types of flies are known for their biting habits, each with unique characteristics and preferred habitats.
- Horse and Deer Flies: Horse and deer flies (family Tabanidae) are large insects found near water and wooded areas. Female horse flies have scissor-like mouthparts that cut skin, causing painful, bleeding bites. Deer flies are smaller, with patterned wings and large eyes; their bites also target the head and neck.
- Stable Flies: Stable flies resemble house flies but have a piercing proboscis. Both male and female stable flies feed on blood, typically targeting ankles and lower legs with a sharp, needle-like prick.
- Black Flies: Black flies, or buffalo gnats, are small, dark, hump-backed flies that breed in fast-flowing water. Their bites create a small puncture wound, leading to swelling and itching, often around the head or face.
- Biting Midges: Biting midges, or “no-see-ums,” are minute flies (less than 1/16 inch long) whose bites feel like a burning sensation and result in intensely itchy, red welts. These tiny insects can pass through window screens.
Reactions and Bite Prevention
Reactions to Fly Bites
Reactions to fly bites commonly include localized itching, redness, and swelling. Symptom intensity depends on individual sensitivity and fly species. Black fly bites can cause “black fly fever,” with headache, nausea, fever, and swollen lymph nodes. Most fly bites are not serious, but secondary infections can occur from scratching. Some biting flies, like certain deer flies, can transmit diseases such as tularemia.
Preventing Fly Bites
To prevent fly bites, wear light-colored, long-sleeved shirts and long pants, as flies are attracted to dark colors. Insect repellents with DEET or picaridin are effective. Avoiding areas with high fly activity, like swampy or muddy environments where flies lay eggs, further reduces exposure.