Many believe all flies bite, particularly the common house fly. However, most common house flies lack the mouthparts to bite humans. Numerous other fly species do bite, and understanding these differences is important for identifying potential threats and taking appropriate preventative measures.
The Common House Fly
The common house fly (Musca domestica) does not bite humans. Its mouthparts are a soft, fleshy proboscis designed for sponging and lapping up liquids, not piercing skin. These flies often regurgitate digestive enzymes onto solid food sources to liquefy them before consumption. While house flies do not bite, they are a health concern. They frequently land on decaying matter, garbage, and feces, picking up and transferring bacteria and pathogens to human food and surfaces, posing a risk of disease transmission.
Flies That Bite Humans
Many other fly types bite humans, often for a blood meal necessary for female reproduction. Stable flies (Stomoxys calcitrans), also known as biting house flies, strongly resemble common house flies but possess a sharp, piercing proboscis that protrudes forward from their head. These flies deliver a painful bite and commonly target the ankles and legs.
Horse flies (Tabanus spp.) and deer flies (Chrysops spp.) also deliver painful bites. These larger flies use scissor-like mouthparts to cut skin, causing blood to flow, which they then lap up. Females require blood meals for egg production.
Identifying Biting Flies
Distinguishing between a common house fly and a biting fly often involves observing specific physical characteristics and behaviors. Common house flies are dull gray, about 6-7 mm long, and have four dark stripes on their thorax. Their sponging mouthparts are visible as a fleshy, non-protruding structure. House flies usually rest with their bodies parallel to the surface.
In contrast, stable flies are similar in size and color to house flies but possess a distinct, bayonet-like proboscis that extends from their head, which they use for piercing. Stable flies often have a checkerboard pattern on their abdomen and tend to rest with their head elevated.
Horse flies are larger, ranging from 10-30 mm, with robust bodies and often large, iridescent eyes. Deer flies are generally smaller than horse flies but larger than house flies, with characteristic dark bands on their wings and often brightly colored eyes. Both horse and deer flies have visible, blade-like mouthparts designed for cutting skin.
Preventing Bites and Managing Reactions
Preventing Bites
Preventing bites from blood-feeding flies involves several strategies:
Wear long-sleeved shirts, long pants, and light-colored clothing to reduce exposed skin.
Use insect repellents containing DEET or picaridin on exposed skin.
Consider permethrin-treated clothing, but do not apply permethrin directly to skin.
Maintain a clean environment by removing decaying organic matter like grass clippings, compost, and animal waste to reduce breeding grounds.
Screen windows and doors to prevent flies from entering indoor spaces.
Managing Reactions
If a bite occurs, clean the affected area with soap and water to prevent infection. Apply a cold compress or ice pack to reduce pain and swelling. Over-the-counter anti-itch creams, such as hydrocortisone, or oral antihistamines can alleviate itching and discomfort. Seek medical attention for severe swelling, spreading redness, fever, or signs of an allergic reaction like difficulty breathing or hives.