Flies are a diverse group of insects found globally. While many are harmless or even beneficial, a select number are known for their ability to bite. Understanding which flies bite and why helps in navigating outdoor environments and protecting oneself from these insects, which can range from minor irritants to pathogen carriers.
The Biting Distinction
Not all flies can bite; this ability depends on their specialized mouthparts. Non-biting flies, such as the common house fly, possess sponging mouthparts designed to absorb liquids from surfaces and cannot pierce skin to feed. In contrast, biting flies feature piercing-sucking mouthparts or structures that cut into the skin.
Flies bite humans and animals to obtain a blood meal. This blood is particularly important for female flies, providing proteins and nutrients necessary for egg development. Without a blood meal, many female biting flies cannot reproduce. When feeding, a biting fly inserts its mouthparts into the skin, lacerates small blood vessels, and injects saliva containing anticoagulants to ensure continuous blood flow.
Common Biting Flies
Mosquitoes are common biting flies, slender insects with long legs and a prominent proboscis. Female mosquitoes feed on blood. They are commonly found near standing water sources like ponds, marshes, and small puddles, where their larvae develop. Their size ranges from 3 to 6 millimeters.
Horse flies are large, robust insects, up to 3 centimeters long, with stout bodies and distinctive, often iridescent eyes. Strong fliers, they are prevalent near water bodies, wetlands, and wooded areas where their larvae mature. Deer flies are smaller than horse flies, about the size of a house fly, identified by clear wings with dark bands. They are found in similar habitats, especially near streams, swamps, and forests.
Stable flies, sometimes called biting house flies, resemble common house flies but have a rigid, bayonet-like proboscis extending from their head. These gray flies have dark stripes on their thorax and a checkered pattern on their abdomen. They are common in agricultural settings, around livestock, and near decaying organic matter like manure or rotting hay. They often target the lower legs of animals and humans.
Black flies, also known as buffalo gnats, are small, stout insects less than 3 millimeters long, with a characteristic humpbacked appearance. They are dark-colored and associated with fast-flowing rivers and streams, where their larvae attach to submerged rocks. Sand flies are tiny, hairy insects, about a quarter the size of a mosquito, with a moth-like appearance and hairy wings. They are common in tropical and subtropical regions, found in sandy areas, and active during warm hours.
Biting midges, often called “no-see-ums” or “punkies,” are minute flies less than 3 millimeters long, making them difficult to see. Despite their small size, they deliver painful bites. These flies are found near coastal areas, lakes, and marshes, thriving in moist soil and decaying vegetation where their larvae develop.
Identifying Their Bites
Bites from different fly species often manifest with distinct characteristics on human skin. Mosquito bites present as small, raised, itchy bumps that appear within minutes. These welts can be puffy, reddish, and sometimes show a small dark spot at the center. The itching can be intense.
Horse fly bites are painful and immediately noticeable due to the fly’s cutting mouthparts, which create a small wound. These bites result in a raised, red or discolored welt that may be sensitive to touch and bleed. Swelling and a burning sensation are common, and the affected area can become tender.
Deer fly bites are also painful, described as a sharp sting. They produce a red, raised bump that is intensely itchy and may develop a small, clear blister in the center. Swelling around the bite area is a common reaction to the fly’s saliva.
Stable fly bites are described as a sharp, needle-like prick. These bites occur on the ankles and lower legs, appearing as red rashes and small, raised red bumps. While painful, they are considered less severe than horse or deer fly bites.
Black fly bites resemble mosquito bites, forming small, inflamed bumps on the skin. A tiny puncture hole may be visible at the center. The bites can cause a burning sensation, soreness, and localized swelling and itching, which may persist for several days.
Sand fly bites are painful and can cause red bumps and blisters. They are intensely itchy and may appear in clusters. The itching can be persistent, and sometimes the bites may become weepy or develop into open sores if excessively scratched.
Biting midge bites, despite the insects’ small size, are painful and intensely itchy. They manifest as small, red, itchy bumps, and sometimes blisters form. The itching may not become apparent for several hours after exposure.
Minimizing Exposure
Reducing the likelihood of being bitten by flies involves several practical measures:
- Wearing appropriate clothing, such as light-colored, long-sleeved shirts and long pants, can deter some species and prevent bites.
- Covering exposed skin is important during peak biting times, which vary by species but often include dawn, dusk, or daytime hours.
- Using insect repellents containing active ingredients such as DEET or picaridin on exposed skin provides effective protection by creating a barrier that discourages flies from landing and biting.
- Avoiding areas where biting flies are abundant, such as stagnant water, marshes, or dense wooded areas, particularly during their active periods, can reduce exposure.
- Eliminating potential breeding sites around homes, such as standing water and decaying organic matter, can decrease local fly populations.