It’s a common summer annoyance: the persistent buzz and irritating bite of flies. While house flies are known for their nuisance value around food, many people wonder, Do Flies Bite Humans? The answer is yes, some flies do bite, and these bites can range from mildly irritating to potentially disease-transmitting. While mosquitoes often take the blame for most biting incidents, a variety of other fly species are also culprits. This article will explore the world of biting flies (excluding mosquitoes, which are covered extensively elsewhere), helping you identify them, understand why they bite, and learn effective methods to manage and prevent bites.
Deer flies and horse flies, stable flies, black flies, biting midges, and sand flies all belong to the biting fly group. Understanding these different types of flies can help you better protect yourself and your family from their unwelcome bites.
Identifying Common Biting Flies
Several types of flies are known to bite humans, each with distinct characteristics and biting habits. Recognizing these flies is the first step in understanding and managing them.
Deer Flies and Horse Flies (Tabanidae)
Deer flies and horse flies are among the larger and more noticeable biting flies. Deer flies, typically around ¼-inch long (about the size of a house fly), are often yellow-brown to black with distinctive dark bands on their wings. Some species exhibit vibrant iridescent green eyes. Horse flies are larger, sometimes reaching an inch or more in length. They can be entirely black or, in the case of “greenheads,” light brown with striking shiny green eyes.
Deer fly and horse fly larvae are aquatic, and adults are commonly found near streams, lakes, ponds, marshes, and swamps. They are notorious for their persistent buzzing around people’s heads, especially in areas with large populations. Both deer flies and horse flies possess scissor-like mouthparts that slice into the skin to access blood, resulting in bites that can be quite painful. In the United States, deer flies are notable as one of the few types of flies capable of transmitting diseases to humans, specifically tularemia, also known as “rabbit fever.”
Stable Fly (Stomoxys calcitrans)
The stable fly is often mistaken for a house fly due to its similar size (around ¼-inch long) and grayish color with four dark stripes on its thorax. However, a key distinguishing feature of the stable fly is its pointed proboscis, which protrudes from beneath its head and is used for blood-sucking.
Stable flies are most prevalent in late summer and fall and are known to travel several miles to find hosts, including livestock, pets, and humans. They typically bite in the early morning or late afternoon, often targeting the ankles and inflicting a sharp, stabbing pain. Stable flies breed in decaying vegetable matter like haystacks, grass clippings, manure, and shoreline vegetation.
Black Flies (Simuliidae)
Black flies, also known as “buffalo gnats,” are small, typically no more than 1/8-inch long, with broad wings and a characteristic humpbacked appearance. These flies thrive in moist environments and are commonly found near creeks and rivers where their larvae attach to submerged stones.
While black flies do not transmit diseases to humans in the United States, their bites can be a significant nuisance and even pose a threat to livestock and, in rare cases, humans when present in large numbers. Black fly bites can cause considerable swelling, bleeding, and persistent itching, and they are known to target the head and areas where clothing fits tightly.
Biting Midges (Ceratopogonidae)
Biting midges are incredibly small, often no more than 1/32 of an inch long, and are sometimes called “punkies,” “no-see-ums,” or simply “gnats.” Their minute size allows them to penetrate standard window and door screens, making them particularly challenging to keep out.
Biting midges are serious pests in coastal areas and near bodies of water like lakes, ponds, and rivers. They bite both during the day and at night. The larvae of biting midges, which are worm-like and tiny, live in damp environments such as moist sand or soil, rotting vegetation, and tree holes.
Sand Flies (Psychodidae)
Sand flies are related to non-biting drain flies. Adult sand flies are small, long-legged, and hairy, measuring no more than 1/8-inch long, and range in color from brown to gray. Their wings are distinctively held in a “V” shape when at rest.
Sand fly larvae are also tiny and worm-like, inhabiting moist, decaying plant matter, moss, mud, or water. Most sand fly species feed on the blood of mammals, reptiles, and amphibians at night. In certain regions, including southern Texas in the United States, some sand fly species are suspected vectors of cutaneous leishmaniasis, a disfiguring protozoan disease in humans.
Why Do Flies Bite Humans?
Understanding why flies bite humans requires a look into their feeding habits and life cycle. Primarily, it’s the female flies that bite. Like mosquitoes, female biting flies require a blood meal to obtain the necessary proteins and nutrients for egg development. The blood meal is not for their sustenance but for reproduction.
Biting flies locate their hosts through a combination of sensory cues. They are attracted to:
- Carbon Dioxide and Moisture: Exhaled breath, rich in carbon dioxide and moisture, is a major attractant.
- Dark Colors and Movement: Dark clothing and movement can make you more visible to biting flies.
- Warmth and Perspiration: Body heat and perspiration also serve as attractants.
Once a suitable host is located, the biting fly uses its specialized mouthparts to pierce the skin. Unlike mosquitoes that have a needle-like proboscis, many biting flies, like deer flies and horse flies, lacerate the skin with scissor-like mouthparts. To ensure a continuous flow of blood, they inject saliva containing anticoagulants. It is this saliva that often triggers allergic reactions and itching in sensitive individuals. In some cases, this saliva can cause severe allergic reactions.
Managing Biting Flies Around Your Home
Controlling biting flies can be challenging because their larval habitats are often hidden or widespread. However, several strategies can help reduce their populations and minimize their impact.
- Sanitation: Eliminating breeding sites is crucial for some species. Stable flies, for instance, breed in decaying organic matter. Removing piles of hay, straw, grass clippings, manure mixed with plant matter, and decaying vegetation, especially along shorelines, can significantly reduce stable fly populations. Similarly, managing decaying vegetation can help control biting midges and sand flies.
- Exclusion: Using screens on windows and doors is a fundamental step in preventing flies from entering homes and buildings. For very small flies like biting midges, finer mesh screens may be necessary.
- Fans and Smoke: In smaller outdoor areas, fans can disrupt the flight of smaller flies, making it harder for them to land and bite. Similarly, smoke from candles or torches can deter smaller species due to air currents and the smoke itself.
- Pesticide Application: Pesticides can be used, but their effectiveness is often limited.
- Ultra-low volume (ULV) treatments and space sprays: These are best for temporary relief in areas with high fly concentrations. They only kill flies on contact and provide no residual protection.
- Residual pesticides: Applying residual pesticides to surfaces where flies rest, like vegetation and walls, can be somewhat effective if flies land on treated surfaces.
- Larviciding: For flies with aquatic larvae, larvicides can be used. Bacillus thuringiensis (BTI) and growth regulators like methoprene are effective against mosquito larvae and BTI has been used against black fly larvae in streams.
Preventing Biting Fly Bites
Personal protection is key to avoiding bites from these persistent pests.
- Repellents: Insect repellents containing DEET or picaridin are effective against biting flies, although they may be less effective than against mosquitoes. Apply repellents to exposed skin, following product instructions carefully.
- Protective Clothing: Wearing heavy-duty, light-colored clothing, including long-sleeve shirts, long pants, and hats, can significantly reduce exposed skin and thus the chances of bites.
- Avoid Peak Biting Times and Habitats: Biting flies often have peak activity periods, such as dawn and dusk, or specific habitats like wooded areas or near water. Avoiding these times and places can reduce exposure.
- Head Netting: In areas with high black fly populations, head nets, similar to bee bonnets, provide excellent protection for the face and neck.
- Lotions and Oils: For very small biting flies like midges, applying heavy lotions or oils to the skin can create a physical barrier, making it harder for them to bite.
Conclusion
So, do flies bite humans? Yes, a variety of fly species do bite humans for a blood meal, primarily female flies needing protein for egg production. While often less associated with biting than mosquitoes, flies like deer flies, horse flies, stable flies, black flies, biting midges, and sand flies can be significant pests. Understanding the types of biting flies, their behavior, and effective management and prevention strategies is crucial for minimizing their impact and protecting yourself and your family from their irritating and potentially disease-transmitting bites. By combining preventive measures with fly management techniques, you can significantly reduce encounters with these vexing pests and enjoy the outdoors more comfortably.
Photos and illustrations courtesy of the U.S. Centers for Disease Control and Prevention, Alex Wild (University of California, www.myrmecos.net ), Jim Kalisch (University of Nebraska) and Ohio State University.
NOTE: When pesticides are used, it is the applicator’s legal responsibility to read and follow directions on the product label.
