While many flies are harmless, certain species bite to feed on blood. These blood-feeding flies are often encountered by humans and animals, and understanding their characteristics is important for managing their presence.
The Purpose of Biting in Flies
Biting in flies is primarily a reproductive strategy for the female. Only female flies bite, as they require proteins from blood to produce viable eggs. This physiological need, known as hematophagy, drives their search for a blood meal. While most flies sustain themselves on other food sources like plant nectar, blood is essential for female reproduction. When a female fly bites, she injects saliva containing anticoagulants to prevent the blood from clotting, allowing her to feed efficiently.
Larger Blood-Feeding Flies of Open Spaces
Larger biting flies frequently inhabit outdoor, open environments, and include species such as horse flies, deer flies, and stable flies.
Horse flies (family Tabanidae) are robust insects, often 0.75 to 1.25 inches long, with stout bodies and large, brightly colored eyes. They are found near water bodies and damp, brushy areas where their larvae develop. Female horse flies possess blade-like mouthparts that cut into the skin, creating a painful wound from which they lap up blood. This feeding often results in immediate pain and localized swelling.
Deer flies (genus Chrysops), also part of the Tabanidae family, are smaller than horse flies, typically 0.25 to 0.5 inches long. They often have distinctive dark bands on their wings and large, iridescent eyes. Deer flies are prevalent in wooded areas near water sources. Their bites are painful, as they use scissor-like mouthparts to slice the skin and feed on blood.
Stable flies (Stomoxys calcitrans) resemble common house flies but are distinguished by a prominent, bayonet-like proboscis that protrudes forward from their head. Both male and female stable flies feed on blood, which is unusual among biting flies. They are often found in agricultural settings, particularly around livestock stables, and breed in decaying organic matter mixed with manure or damp hay. Stable flies inflict a painful bite, typically targeting the legs and ankles of humans and animals.
Smaller Biting Flies of Specific Habitats
Smaller biting flies are often associated with specific environmental conditions, thriving in damp or aquatic habitats.
Black flies (family Simuliidae), also known as buffalo gnats, are small, dark insects, typically 2 to 5 millimeters long, with a distinctive humpbacked appearance. They breed exclusively in clean, flowing water, such as rivers and streams. Female black flies bite, using mouthparts that cut into the skin, causing a painful bite that can result in bleeding, itching, and swelling. These bites can sometimes lead to a reaction known as “black fly fever,” characterized by symptoms like headache and nausea.
Sand flies (subfamily Phlebotominae) are small, fuzzy flies, usually 1 to 5 millimeters in length, often found in damp soil, tree holes, or other moist, sheltered environments. Female sand flies feed on blood, and their bites are known for causing itchy welts. They are generally active at night.
Biting midges (family Ceratopogonidae), also widely known as “no-see-ums” or “punkies,” are extremely small, often less than 1/8 inch long. They are gray with patterned wings and found in various moist habitats, including coastal salt marshes and decaying vegetation. Female biting midges take blood meals. Their bites, despite their tiny size, can be surprisingly painful, causing a burning sensation and itchy, red welts.
Mosquitoes: Ubiquitous Blood-Feeders
Mosquitoes (family Culicidae) are among the most recognized and widespread biting insects globally. These slender-bodied flies have a single pair of wings and long legs. Their life cycle is linked to water, as eggs are laid on or near water, where larvae and pupae develop before emerging as flying adults.
Only female mosquitoes feed on blood, requiring proteins and iron for egg production. Male mosquitoes primarily sustain themselves on plant nectar. When a female mosquito bites, she uses specialized piercing-sucking mouthparts to penetrate the skin and draw blood, injecting saliva.