All You Need to Know About Flies That Bite

Flies, for many, are merely a buzzing annoyance—a pest that circles fruit bowls and light fixtures. These tiny winged creatures often conjure images of summertime picnics, lazy afternoons, and the inevitable swatting gestures that accompany their presence. However, there’s more to these seemingly innocuous insects than meets the eye. While most flies are harmless and only seek decaying organic material, some are capable of delivering surprisingly painful bites. This lesser-known behavior not only changes our understanding of these ubiquitous insects but also brings to light potential health concerns and the need for prevention.

The Anatomy and Evolution of Biting Flies

Flies, part of the order Diptera meaning “two wings,” are fascinating not just for their wings, but for their varied mouthparts. The mouth anatomy differs notably between species, but those designed to bite have evolved specialized structures for the task. The biting flies possess a proboscis, a lengthy and flexible appendage, tailored for piercing and sucking. This proboscis houses sharp instruments such as mandibles and maxillae, adept at slicing through skin. On the flip side, flies that don’t bite often have sponge-like mouthparts perfect for absorbing liquid nutrients.

Distinction Between Biting and Non-Biting Flies

The mouthpart anatomy plays a crucial role in differentiating biting flies from their non-biting counterparts. Flies like horse flies and deer flies have evolved mandibles and maxillae resembling sharp blades, facilitating a stinging bite. In stark contrast, a common housefly’s mouth contains a labellum, a spongy structure tailored for soaking up liquids, indicating its non-biting nature.

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Evolutionary Advantages of Biting for Flies

Biting flies have evolved this trait due to the immense survival benefits it provides. Extracting blood offers these flies a protein reservoir, indispensable for their reproductive mechanisms. For instance, female mosquitoes rely heavily on blood-derived proteins and iron to nurture their eggs. This evolutionary adaptation not only boosts their reproductive prowess but also aids in sustaining varied environments by widening their nutritional spectrum.

Not All Flies Bite: Understanding the Species Differentiation

Among the myriad of fly species gracing our planet, only a handful have the capability to bite. Various families of biting flies exist, each bearing unique characteristics.


Often regarded as the most notorious, these vectors are responsible for transmitting ailments like malaria and dengue. Only the female mosquito indulges in blood-sucking, using her finely-tuned proboscis.

Horseflies and Deer Flies

Their distinct size and swift flight patterns make them easily recognizable. Equipped with a pair of scissor-like mouthparts, their bites can be quite painful. These flies are particularly attracted to movement, warmth, and exhaled carbon dioxide.


These minuscule creatures, despite their size, are adept at transmitting diseases such as Leishmaniasis. Their proboscis might be short, but their blood-sucking efficiency is unparalleled.

Black Flies

Distinguished by their humped backs, these flies are notorious for their biting prowess, especially in areas adjacent to running water bodies.

It’s essential to note, however, that numerous fly species, like fruit flies and drain flies, are harmless and refrain from biting humans. Distinguishing between these various species and understanding their behaviors can go a long way in avoiding their often painful bites.

The Experience of a Fly Bite

Anyone who’s spent a summer evening outdoors knows the all-too-familiar pinch of an insect bite. However, not all bites are the same, and the culprit can often be identified by the bite’s appearance and sensation.

Physical Appearance of the Bite

Fly bites, especially those from larger flies like horseflies, often appear as a small, red, inflamed area with a central dark spot where the bite occurred. The edges might look ragged because these flies cut into the skin to access blood. In contrast, mosquito bites usually manifest as raised, round, pink welts that can grow in size due to scratching. Other insect bites, such as those from bed bugs or fleas, can appear as small red bumps, sometimes in a linear or clustered pattern. 

Sensations and Reactions to Fly Bites

The immediate sensation of a fly bite, particularly from biting flies like horseflies or deer flies, can be sharp and painful. This intense pain can be attributed to their scissor-like mouthparts, which slice the skin rather than piercing it. Following the bite, the area might become itchy, and the discomfort can last longer than the typical mosquito bite. Some individuals might also experience swelling or even allergic reactions, characterized by excessive redness, warmth, and in rare cases, symptoms like dizziness or difficulty breathing. It’s important to monitor bites for signs of infection or prolonged symptoms, especially if the bite doesn’t improve after a few days or if there’s an escalation in pain, redness, or swelling.

Why Some Fly Bites Itch More Than Others

The intensity of itching and discomfort from a fly bite can be influenced by several factors. Firstly, when a fly bites, it injects saliva into the wound. This saliva contains anticoagulants and enzymes to assist in feeding, but it’s also these substances that can trigger an immune response in humans. The body’s immune reaction results in the release of histamines, which cause itching and inflammation. Different individuals might have varying sensitivity levels to these substances, leading some to experience more intense itching than others. Additionally, specific species of flies might inject different compounds or quantities of saliva, potentially causing variation in the itchiness of their bites. Furthermore, repetitive exposure to bites from the same species can either heighten sensitivity, leading to more intense reactions, or in some cases, cause desensitization, resulting in milder reactions over time.

Typical Healing Duration of a Fly Bite

A typical fly bite usually starts to heal within a few days. The initial redness and swelling tend to subside within 24 to 48 hours, and the itching should decrease during this time as well. However, several factors can influence the healing process. Scratching the bite can introduce bacteria to the wound, increasing the risk of infection and potentially prolonging the healing time. Bites that become infected may exhibit increased redness, warmth, pus, or even a spreading red streak, and they might take longer to heal, potentially lasting a week or more. Additionally, individual immune responses can play a role; those with more sensitive skin or allergic reactions to the bite might experience prolonged symptoms. As a general rule, if a bite doesn’t show signs of improvement after a week, or if symptoms worsen, it’s advisable to seek medical attention.

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Health Implications and Risks of Fly Bites

Beyond the initial discomfort, certain biting flies can transmit diseases or cause infections, making awareness of their health implications essential.

Diseases That Can Be Transmitted Through Fly Bites

Several fly species are vectors for various diseases that can affect human health. For instance:

  • Mosquitoes (Culicidae) – Known carriers of several viruses including the West Nile virus, Zika virus, dengue, and chikungunya. They can also transmit the Plasmodium parasite responsible for malaria.
  • Sandflies (Phlebotominae) – The primary vectors for Leishmaniasis, a disease caused by Leishmania parasites which affect both the skin and internal organs.
  • Tsetse Flies – Transmit trypanosomes, which cause Sleeping Sickness (African trypanosomiasis) in humans.
  • Black Flies (Simuliidae) – Can spread Onchocerca volvulus, a parasitic worm causing onchocerciasis or river blindness.

Overall Health Risks Associated with Fly Bites

Beyond disease transmission, fly bites can also lead to other health issues. The physical act of biting can cause pain, swelling, itching, and inflammation. In some individuals, especially those with sensitive skin, bites can result in allergic reactions, leading to increased redness, swelling, and blistering. Continued scratching of the bite site can introduce bacteria, leading to secondary bacterial infections like cellulitis. Moreover, severe allergic reactions to fly bites, although rare, can lead to anaphylaxis, a life-threatening condition requiring immediate medical intervention.

Treatment of Fly Bites at Home

If bitten by a fly, there are several steps you can take at home to alleviate symptoms and promote healing:

  • Clean the Area – Wash the bite gently with soap and water.
  • Cold Compress – Applying a cold pack or cloth dipped in cold water can help reduce swelling and soothe itching.
  • Topical Treatments – Over-the-counter creams containing hydrocortisone, calamine, or a topical antihistamine can help relieve itching and inflammation.
  • Oral Antihistamines – These can be taken to reduce allergic reactions and itching.
  • Avoid Scratching – As difficult as it might be, it’s essential to avoid scratching the bite area to prevent secondary bacterial infections.
  • Pain Relievers – Over-the-counter pain relievers like acetaminophen or ibuprofen can help reduce pain and inflammation.

If a bite appears infected or if you experience severe symptoms, it’s crucial to consult a healthcare professional.

Behavioral Aspects and Patterns of Biting Flies

A fly’s decision to bite isn’t random; it’s influenced by a variety of factors, from the clothes we wear to the animals around us and even the time of day.

Factors That Attract Flies to Certain Individuals

When outdoors, especially in areas prone to biting flies, one might wonder why some people seem to be more targeted than others.

  • Carbon Dioxide – We exhale carbon dioxide every time we breathe, and higher concentrations can attract flies. Individuals who are larger or exerting themselves might produce more CO2, making them prime targets.
  • Body Heat – Biting flies, especially mosquitoes, are drawn to warmth. Hence, someone who’s warmer may seem more attractive.
  • Scent and Skin Secretions – Certain chemicals present in sweat, perfumes, or soaps can be more enticing to flies. Similarly, some studies suggest that blood type might play a role, with certain blood types being more attractive to biting flies.
  • Lactic Acid, Uric Acid, and Ammonia – These substances, found in sweat, can draw flies closer.

The thickness and type of fabric play a role in a fly’s ability to bite through clothing. Light, breathable summer fabrics may not offer complete protection against biting flies, especially if they sit close to the skin. However, wearing light-colored clothing can be helpful, as flies are often attracted to darker colors.

Animal Victims: Do Flies Bite Other Creatures?

Many species of biting flies, such as horse flies, are more attracted to animals than humans. They frequently target livestock, causing not just painful bites but also transmitting diseases amongst the herd. Wildlife, especially larger mammals, also faces regular fly attacks. Such interactions can lead to reduced weight gain in livestock or even disease transmission in wildlife populations.

Activity Patterns: Times of the Day and Year When Fly Bites Are More Common

Biting flies have specific times when they’re most active. For example:

  • Mosquitoes – Typically most active during dawn and dusk, although there are species that bite throughout the day.
  • Sandflies – Prefer to bite in the evening and at night.
  • Horseflies – Are diurnal, meaning they’re most active during the day.

The prevalence of fly bites can also be seasonal. In many temperate areas, summer is the prime time for biting flies due to the warmer weather and increased breeding activity. However, in tropical regions, fly activity might be influenced more by rainfall patterns than by temperature.

Geographic and Demographic Considerations

Biting fly activity varies across regions and demographics, with certain areas experiencing higher risks and some individuals being more susceptible to bites.

Regions More Prone to Biting Flies

The prevalence of biting flies varies globally, influenced by factors like climate, ecosystem type, and human activities.

  • Tropical Regions – Warm, humid conditions are perfect for many biting fly species, especially mosquitoes. Regions such as sub-Saharan Africa, Southeast Asia, and parts of South America are particularly impacted, with the presence of diseases like malaria and dengue adding to the problem.
  • Wetlands & Marshes – Any area with stagnant water is a potential breeding ground for flies like mosquitoes. Hence, regions with abundant wetlands, marshes, or ponds often see higher fly activity.
  • Forest Areas – Deep forests, especially tropical rainforests, are home to a variety of biting fly species, including certain types of biting midges and sandflies.
  • Agricultural Areas – Places with significant livestock presence, like cattle farms, can attract biting flies such as horseflies or stable flies.

Are Children More Susceptible to Fly Bites Than Adults?

While biting flies don’t necessarily have a preference for children over adults in terms of attraction, children may experience bites more frequently or severely due to several reasons:

  • Behavior – Children often play outside and might be less aware of the presence of flies or of taking preventive measures against them.
  • Skin Sensitivity – Children’s skin can be more sensitive than adults’, leading to more pronounced reactions to bites. They might experience more swelling, redness, or itching from the same bite that might cause a milder reaction in an adult.
  • Immune Response – Children might not yet have been exposed to as many bites as adults and, as a result, may have stronger immune reactions to fly saliva. Over time and with repeated exposure, some individuals can become desensitized to bites, leading to milder reactions.

While children aren’t inherently more attractive to biting flies, their behaviors, sensitive skin, and immune responses can make them more susceptible to pronounced reactions from fly bites.

Preventative Measures and Repellents

With the right knowledge and tools, it’s possible to significantly reduce the risk of fly bites, ensuring a more comfortable and safer outdoor experience.

Best Practices to Prevent Fly Bites

Preventing fly bites is not only a matter of comfort but also of health, especially in areas where flies are vectors for diseases. Here are some best practices:

  • Wear Protective Clothing – Long sleeves, pants, and hats can help keep flies away from the skin. Light-colored clothing can be especially helpful, as many flies are attracted to darker colors.
  • Avoid Peak Times – If possible, avoid outdoor activities during times when biting flies are most active, such as dusk and dawn for mosquitoes.
  • Maintain Your Yard – Eliminate standing water in your yard, which can serve as breeding grounds for mosquitoes. Regularly empty items like birdbaths, flowerpots, and gutters.
  • Use Netting and Screens – If you’re sleeping or resting in an area with many flies, use bed nets or ensure that windows and doors have tight-fitting screens.
  • Stay Aware in Endemic Areas – If you’re traveling to or living in an area known for diseases transmitted by flies, stay updated on local advisories and take additional precautions.

Effective Repellents Against Biting Flies

Repellents are essential tools in the fight against biting flies:

  • DEET – Perhaps the most recognized insect repellent, DEET is effective against a wide range of biting flies. It’s available in various concentrations, with higher percentages providing longer protection.
  • Picaridin – Often seen as an alternative to DEET, Picaridin repels a broad spectrum of biting flies and has the added advantage of being odorless and less sticky.
  • Oil of Lemon Eucalyptus (OLE) – A natural alternative, OLE has been found to be as effective as DEET against mosquitoes. However, it’s not suitable for children under 3 years of age.
  • IR3535 – This is another effective repellent ingredient that works against various biting flies.
  • Permethrin – While not a repellent in the traditional sense, permethrin can be applied to clothing, shoes, and gear to repel and kill biting flies.

When choosing a repellent, it’s vital to consider the types of flies in the area, the duration of exposure, and any personal or health concerns. Always apply repellents as directed on the label, ensuring comprehensive coverage for maximum protection.


The world of biting flies is vast and varied, with these tiny creatures having an impact that belies their size. From the painful bite of a horsefly to the disease-transmitting potential of mosquitoes, it’s evident that these insects are not just minor annoyances but can pose real threats to our health and well-being. Understanding the behavior, anatomy, and biology of these flies gives us insight into their motivations and mechanisms, further emphasizing the need for protection and prevention. Knowledge is our first line of defense. By being aware of the risks associated with biting flies and the reasons they bite, we are better equipped to protect ourselves. But beyond personal protection, a collective awareness in communities can lead to larger scale efforts in controlling fly populations and reducing the spread of fly-borne diseases. Whether it’s the simple act of wearing repellent, educating others, or supporting community efforts in fly control, every action contributes to a safer environment for all. The fight against biting flies isn’t just about avoiding itchy bites; it’s about safeguarding our health, the health of our loved ones, and the well-being of communities around the world.

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