You’re enjoying a summer afternoon in Kentucky when you feel a sudden, sharp pain on your arm. You swat at the culprit, but it’s already gone—or maybe you never saw it in the first place.
Biting flies are persistent pests across the Bluegrass State, and knowing which species you’re dealing with can help you protect yourself and understand what to expect from that painful bite.
Kentucky’s warm summers and abundant water sources create ideal conditions for several species of biting flies. The most common in Kentucky are the horse fly and deer fly, but you’ll also encounter stable flies, black flies, biting midges, and sand flies throughout the state.
Each species has distinct characteristics, behaviors, and bite patterns that can help you identify your attacker.
1. Deer Fly
The deer fly (Chrysops species) is one of the most recognizable biting flies you’ll encounter in Kentucky. Deer flies, which commonly bite humans, are smaller with dark bands across the wings and colored eyes similar to those of horse flies. These flies typically measure between 1/4 to 1/2 inch long and display black or brownish coloring that makes them easy to spot when they’re hovering around your head.
What makes deer flies particularly frustrating is their persistent behavior. You might be sitting at a picnic table and have to keep shifting your legs because a little deer fly bites at your ankle. They’re attracted to movement, shiny surfaces, carbon dioxide, and warmth—all signals that indicate a potential blood meal. Unlike some biting insects that bite quickly and leave, deer flies circle around their victims and pursue relentlessly until they feed or are killed.
The bite itself is notably painful because they use their scissor-like mouthparts to open skin, so deer fly bites are rather painful. After feeding, you’ll likely experience irritation and swelling that typically disappears within a day or so, though secondary infections can occur if you scratch the bite site. According to the University of Kentucky Entomology Department, these flies are most active during specific periods in summer, making certain weeks more challenging than others for outdoor activities.
2. Horse Fly
Horse flies (Tabanus species) are the largest and most intimidating biting flies in Kentucky. Horse flies range in size from 3/4 to 1-1/4 inches long and usually have clear or solidly colored wings and brightly colored eyes. Their size alone can be daunting, and when one starts buzzing aggressively around your head, it’s an experience you won’t soon forget.
These robust flies are powerful fliers that can travel long distances from their breeding sites. Horse flies and deer flies are true flies in the family Tabanidae in the insect order Diptera. The adults are often large and agile in flight. Females parasitize land vertebrates, including humans, biting them to obtain blood. Only female horse flies bite, as they require blood protein to produce eggs, while males feed harmlessly on nectar and plant sugars.
The bite of a horse fly is considered one of the most painful insect bites you can experience. Once on a host, they use their knife-like mouthparts to slice the skin and feed on the blood pool that is created. This cutting action, rather than a simple puncture, causes significant pain and often results in considerable bleeding. The WKMS report on biting flies notes these are particularly tenacious creatures that excel at identifying heat and chemical signatures.
Horse flies commonly attack the legs of humans and animals. Their bites can cause allergic reactions involving hives and wheezing in rare instances, and the irritation may be accompanied by swelling. While the pain is intense initially, it usually doesn’t last long, though you should watch for signs of secondary infection if you scratch the wound.
3. Stable Fly
The stable fly (Stomoxys calcitrans) is roughly the same size as a common house fly but behaves very differently. While house flies are merely nuisance pests, stable flies are aggressive biters that can make outdoor activities miserable. These flies have a strong preference for biting the lower legs, particularly around the ankles, which results in frequent stomping and movement from their victims.
Stable flies develop in decaying organic matter, particularly in areas with livestock manure, wet hay, and decomposing vegetation. This means they’re especially common around farms, stables, and rural properties, but they can travel considerable distances to find hosts. Unlike horse and deer flies that slash the skin, stable flies have piercing mouthparts that they insert into the skin to feed on blood.
The bite of a stable fly produces immediate, sharp pain that’s often described as feeling like a needle stick. The stable fly is a common pest with blood-feeding tendencies, he goes for horses’ lower legs, resulting in a lot of stomping. This stomping and kicking can result in injury, leg wounds, or hoof damage. For humans, the bites typically appear as small red welts that may itch for several hours to a few days.
Stable flies are daytime feeders that are most active during warm, sunny weather. They’re persistent biters that will repeatedly attempt to feed even after being swatted away. The best protection involves wearing long pants and socks when in areas where stable flies are common, and applying repellents containing DEET can provide several hours of relief.
4. Black Fly
Black flies (Simulium species), also called buffalo gnats, are small but fierce biters that have caused significant problems in Kentucky. Black flies or buffalo gnats are 1/8-inch long hump-backed dark flies with wide, clear wings. Females use their sharp, blade-like mouthparts to slice the skin and ingest the blood that wells up. Their distinctive humpbacked appearance and dark coloring make them identifiable once you know what to look for.
In Kentucky, these biting gnats were attacking people in Jefferson County. Historically, black flies have tormented livestock along streams and rivers in McLean, Simpson, Warren, and Webster counties and could be a problem near streams and rivers where the larvae develop. The immature stages live attached to stones and submerged vegetation in flowing water, which is why black fly problems are concentrated near streams and rivers.
Black fly season is relatively short, typically lasting only 2 to 3 weeks in early spring, but when outbreaks occur, they can be intense. The bite may bleed for some time after feeding has stopped and may itch intensely for several days. These flies are attracted by exhaled carbon dioxide and vision, and they swarm around the head, biting around the ears, eyes, and along exposed skin. The Kentucky Pest News reported the last major outbreak in Kentucky occurred in 2014, demonstrating that while annual populations are usually manageable, periodic surges can create serious problems.
Black flies are strong fliers capable of traveling miles from their breeding sites to find blood meals. They feed during the day and are particularly active during warm, humid conditions. Animals under attack may run and injure themselves trying to escape, and in extreme cases, livestock have suffocated from inhaling massive numbers of these gnats.
5. Biting Midge (No-See-Um)
Biting midges (Culicoides species), commonly called no-see-ums, are aptly named because they’re nearly impossible to see with the naked eye. Ceratopogonidae is a family of flies commonly known as no-see-ums, sand flies or biting midges, generally 1–3 millimetres in length.
The family includes more than 5,000 species, distributed worldwide, apart from the Antarctic and the Arctic. Their minuscule size allows them to pass through ordinary window screens, making them particularly troublesome pests.
Despite their tiny size, biting midges deliver disproportionately painful bites. The mouthparts of biting midges consist of a fleshy sheath inside of which are four, minute cutting blades that lacerate the skin, inflicting sharp, burning pain.
Observant victims may notice tiny red “spots” that are biting midges filling with blood. The cutting action of their mouthparts, combined with anticoagulant compounds in their saliva, causes intense burning and itching that can last for days or even weeks.
Biting midges breed in a variety of semi-aquatic habitats including marshes, bogs, saturated soil, and areas with decaying organic matter. They’re most active during dawn and dusk hours, though some species will bite throughout the day in shaded areas. Like other biting flies, only females feed on blood, while males consume nectar and plant sap.
The bites typically appear as small red welts that may cluster together, creating larger areas of irritation. These insects cut into the skin instead of using a proboscis like mosquitoes, which causes intense itching, redness, and welts. Bites can last up to two weeks, and scratching increases the risk of infection.
While biting midges are not known to transmit diseases to humans in the United States, they can cause significant discomfort and allergic reactions in sensitive individuals.
6. Sand Fly
True sand flies belong to the subfamily Phlebotominae of the family Psychodidae, though the term “sand fly” is sometimes loosely applied to biting midges as well. The common name “sand fly” usually is reserved for blood-sucking species in the subfamily Phlebotominae of the family Psychodidae.
There are an estimated 600 species of phlebotomine sand flies in the world, including 14 species in the U.S.. In Kentucky, sand fly encounters are less common than with other biting flies, but they can occur in appropriate habitats.
Sand flies (Phlebotomus and Lutzomyia species) are physically similar to biting midges in size and appearance. An adult sand fly is less than 1/8 inch in length with long legs and wings that form a V shape. Sand fly bites are very painful. Their small size and V-shaped wing position when at rest help distinguish them from other small flies.
In the United States, sand flies pose minimal health risks to humans. Only one of these species bites humans, and it is not known to be involved in the transmission of disease agents. Phlebotomine sand flies are known to be vectors of viruses, bacteria, and protozoa that cause human disease in Asia, Africa, southern Europe, and Latin America. While sand flies in other parts of the world transmit serious diseases like leishmaniasis, the species found in Kentucky and the broader United States don’t carry these pathogens.
Sand flies prefer humid environments and are typically found near their breeding sites in moist organic matter. They’re weak fliers compared to horse flies and deer flies, so they tend to stay close to ground level and are most active during calm, warm evenings.
Their bites produce similar reactions to other biting fly species—red welts, itching, and burning sensations that can persist for several days. The Orkin guide to biting flies notes that while sand flies prey on mammals and reptiles, their impact in Kentucky is relatively minor compared to more common biting fly species.
Conclusion
Understanding the different biting flies in Kentucky helps you take appropriate protective measures. Wearing long sleeves and pants provides a physical barrier, especially during peak activity times for each species. Repellents containing DEET offer several hours of protection, though you should follow label instructions carefully regarding application frequency and age restrictions.
Avoiding peak activity times can significantly reduce your exposure. Most biting flies are most active during daylight hours, with black flies and some midges being particularly aggressive during dawn and dusk. Staying indoors or in screened areas during these times, when practical, provides the best protection.
For your property, eliminating breeding sites helps reduce local populations. This includes removing standing water, managing livestock waste properly, and keeping grass and vegetation trimmed. While large-scale control of biting fly populations is challenging due to their mobility and diverse breeding habitats, these local efforts can make your immediate surroundings more comfortable.
If you experience severe reactions to biting fly bites—including excessive swelling, difficulty breathing, or signs of infection—seek medical attention promptly. Most bites heal on their own with basic first aid, but complications can occur, particularly if bites are scratched excessively or if you have allergies to insect saliva.
