Flies are a common nuisance, buzzing around and often landing on us. While many flies are simply bothersome, some types are equipped to bite, leaving behind itchy and sometimes painful welts. But Why Do Flies Bite Humans? It’s a question many have pondered as they swat away these persistent pests. The answer lies in the fly’s biology and feeding habits, and understanding this can help us better protect ourselves.
The Science Behind Fly Bites: Why They Need Blood
Not all flies bite, and among those that do, it’s typically the females that are the culprits. The primary reason why flies bite humans is for blood. Female biting flies require a blood meal to obtain the necessary protein to develop their eggs. Just like mosquitoes, they are essentially seeking a nutrient-rich source to ensure successful reproduction. Male flies, on the other hand, generally feed on nectar, pollen, and plant juices, and therefore, do not have the biological imperative or mouthparts designed to bite.
The biting mechanism varies among different types of flies. Some, like horse flies and deer flies, possess scissor-like mouthparts that actually slice into the skin to lap up the blood. This is why their bites are often felt immediately and can be quite painful. Others, such as stable flies and mosquitoes (which are technically flies), have piercing-sucking mouthparts that penetrate the skin to draw blood. Regardless of the method, the result is the same: they are after your blood to fuel their reproductive cycle.
Types of Flies That Bite: Know Your Biter
The world of biting flies is diverse, encompassing various species, each with its own preferred habitats and biting habits. Being able to identify the types of flies that bite can help you understand the potential risks and how to best avoid them. Here are some of the most common types of biting flies you might encounter:
Mosquitoes
Alt text: A close-up view of a mosquito feeding on human skin, highlighting its proboscis piercing the skin to draw blood.
Perhaps the most notorious of biting flies, mosquitoes are responsible for more bites on humans globally than any other group. Female mosquitoes are relentless in their pursuit of blood, using their long, piercing proboscis to tap into capillaries. Beyond the itchy welts, mosquitoes are significant vectors of diseases, transmitting illnesses like West Nile virus, Zika virus, and malaria in other parts of the world. Their ability to breed in stagnant water makes them a pervasive problem in many environments.
Horse Flies and Deer Flies
Alt text: A detailed image of a yellow fly perched on a leaf, showcasing its distinctive yellow body and large eyes, typical of horse and deer flies.
Horse flies and deer flies are robust and often intimidating biting flies known for their painful bites. Larger than house flies, they are commonly found in sunny areas, particularly near wooded areas, fields, and bodies of water, as they are attracted to moisture and animals. These flies are equipped with mandibles that work like tiny scissors to cut into the skin, causing a sharp, immediate pain. Their bites can result in significant swelling and irritation, and while they are not typically disease vectors in the same way as mosquitoes in many regions, their bites can be intensely uncomfortable and even provoke allergic reactions in some individuals. Deer flies are often smaller than horse flies but equally aggressive biters.
Stable Flies
Stable flies bear a strong resemblance to house flies, often leading to misidentification, but unlike their non-biting look-alikes, stable flies are blood feeders. They are commonly found around livestock facilities, farms, and coastal areas where decaying organic matter is present, as this is where they breed. Both male and female stable flies feed on blood, typically targeting mammals, including humans, often biting ankles and legs. Their bites are described as sharp and persistent, and they can be quite bothersome, particularly in late summer and early fall when their populations peak.
Black Flies
Black flies, also known as buffalo gnats due to their humped back appearance, are small but aggressive biters. They thrive in flowing water, like rivers and streams, as their larvae develop in these environments. Black flies are notorious for swarming and can deliver painful bites, often targeting the head, neck, and shoulders. Their bites can cause intense itching and swelling, sometimes leading to a condition known as “black fly fever,” a systemic reaction to their saliva in sensitive individuals. They are particularly prevalent in northern regions and areas with fast-flowing water sources.
Sand Flies
Sand flies are tiny, almost gnat-like flies, often barely noticeable until you feel their bite. They are found in tropical and subtropical regions, as well as some temperate areas, and are active during dusk and night. Sand fly bites can be disproportionately painful for their size, and they are vectors of diseases like leishmaniasis in certain parts of the world. They are weak fliers and often found in sheltered, sandy habitats, hence their name.
Yellow Flies
Yellow flies are closely related to deer flies and share similar biting habits and habitats, preferring shaded, humid environments near forests and water bodies, particularly in the southeastern United States. They are named for their yellowish bodies and are known for their persistent and painful bites, similar to deer flies. Yellow fly bites can cause localized swelling, itching, and discomfort, making them a significant nuisance in their regions.
Biting Midges (No-see-ums)
Alt text: A magnified view of biting midges, showcasing their tiny size and delicate wings, highlighting why they are often called “no-see-ums”.
Biting midges, often called “no-see-ums” or punkies, are incredibly small flies, often less than 1/8 inch long. Their diminutive size allows them to penetrate screens and netting, making them a common indoor and outdoor pest. Despite their size, their bites can be surprisingly irritating and itchy, often leaving behind multiple small, red welts. They are most active at dawn and dusk and are often found in humid, coastal areas and near marshes, where their larvae develop.
Snipe Flies
Snipe flies are related to deer flies and are typically found in damp, wooded areas. While many species of snipe flies are not biters, some do possess mouthparts capable of inflicting a bite. However, compared to horse flies or deer flies, snipe fly bites are generally considered less painful and less common. They are often encountered in shaded, forest environments.
Problems Caused by Fly Bites: Beyond the Itch
The immediate reaction to a fly bite is often localized pain, itching, and swelling. This is the body’s inflammatory response to the fly’s saliva, which contains anticoagulants and other compounds that facilitate blood feeding. However, the problems associated with fly bites can extend beyond these immediate symptoms.
- Allergic Reactions: Some individuals can experience more severe allergic reactions to fly bites, characterized by increased swelling, redness, hives, and in rare cases, systemic reactions like difficulty breathing.
- Disease Transmission: As mentioned, certain biting flies, most notably mosquitoes and sand flies, are vectors of various diseases. While horse flies and deer flies are not primary disease vectors in many regions, they have been known to transmit diseases like tularemia and anthrax in some instances and to animals.
- Secondary Infections: Scratching at fly bites, especially intensely itchy bites from mosquitoes or midges, can break the skin and lead to secondary bacterial infections.
Preventing Fly Bites and Controlling Biting Flies
Minimizing exposure and controlling biting fly populations are key strategies to reduce bites and associated problems.
- Personal Protection: Using insect repellents containing DEET, picaridin, or oil of lemon eucalyptus can effectively deter biting flies. Wearing long sleeves and pants, especially during peak biting times (dawn, dusk, and in wooded areas), can also provide a physical barrier.
- Environmental Control: Reducing breeding grounds is crucial. For mosquitoes, this means eliminating standing water in containers, gutters, and other areas around your home. For other biting flies that breed in organic matter, keeping yards clean of decaying vegetation and managing compost and waste effectively can help.
- Professional Pest Control: In areas with heavy biting fly infestations, professional pest control services can provide targeted treatments to reduce fly populations. For example, Orkin Pros can assess your property and implement strategies for fly control, focusing on both adult flies and their breeding sites.
Why do flies bite humans? Ultimately, it’s a matter of survival and reproduction for female flies. While their bites are often unwelcome and uncomfortable, understanding the reasons behind this behavior and the types of flies involved is the first step in taking effective measures to protect ourselves and our surroundings.
