Louisiana’s warm, humid climate and abundant wetlands create ideal conditions for biting flies. These blood-feeding insects are more than just a nuisance—they can cause painful bites, allergic reactions, and in some cases, transmit diseases. Understanding which species you’re dealing with and how to protect yourself can make outdoor activities much more enjoyable throughout the year.
From the ubiquitous mosquito to the tiny no-see-um, you’ll encounter various biting flies across Louisiana’s diverse habitats. Each species has distinct characteristics, behaviors, and peak activity periods that can help you identify them and take appropriate protective measures.
1. Mosquitoes
Mosquitoes (Culicidae family) are perhaps the most recognizable and widespread biting flies in Louisiana. This group includes mosquitoes, black flies, sand flies, biting midges, horse flies, and deer flies among the state’s biting fly population. These slender insects measure between 1/8 to 1/4 inch long and are characterized by their long legs, narrow wings, and distinctive high-pitched whine.
Female mosquitoes require blood meals to produce eggs, while males feed exclusively on plant nectar. You’ll find mosquitoes most active during dawn and dusk, though some species bite throughout the day. They breed in standing water, making Louisiana’s wetlands, drainage ditches, and even water-collecting containers around your home prime breeding grounds.
Mosquito bites typically appear as small, itchy red bumps that develop within minutes to hours after being bitten. The saliva mosquitoes inject while feeding triggers your body’s immune response, causing the characteristic swelling and itching.
To reduce mosquito exposure, eliminate standing water around your property, install or repair window screens, and use EPA-approved insect repellents containing DEET, picaridin, or oil of lemon eucalyptus. Vaccinate horses annually for mosquito-borne viruses, including Eastern equine encephalomyelitis and West Nile virus ahead of your main mosquito season if you keep livestock.
2. Horse Flies
Horse flies (Tabanus species) are among the largest and most painful biting flies you’ll encounter in Louisiana. Horse flies are from 10 to 25 mm (~⅜ to 1 in) in length, with robust bodies and large, often iridescent eyes. Horse-flies are mostly dark brown or black, with dark eyes, often with a metallic sheen.
These aggressive flies are most active during warm weather, with horsefly season in Louisiana starts in March and ends in November. The flies are most active just before sunrise and three hours after sunrise. Another peak in activity is two hours before sunset and just after sunset.
Female horse flies use scissor-like mouthparts to cut through skin and lap up pooling blood. Their bites are immediately painful and can cause significant swelling, redness, and itching that may persist for several days. Horse fly bites are often considered one of the most painful due to their large size and cutting feeding mechanism.
Horse flies are attracted to movement, carbon dioxide, and dark colors. They prefer areas near water where they lay eggs on vegetation. To minimize encounters, avoid wooded, wet areas during peak activity hours and wear light-colored, protective clothing when outdoors.
3. Deer Flies
Deer flies (Chrysops species) are close relatives of horse flies but smaller and equally aggressive. The deer fly Chrysops flavidus is a widespread livestock pest in southeastern U.S., and among the most serious pests of livestock in Louisiana. Adult deer flies range from 1/3 to 2/5 of an inch (7 to 9 mm) in body length, with broad bodies and heads. Deer flies are typically yellow and black in color with black stripes and alternating dark and clear wings.
These flies are particularly notorious for circling around your head before landing to bite. Deerflies feed mainly on head and neck, making them especially annoying during outdoor activities. Their scissor-like mouthparts cut through skin similar to horse flies, causing immediate pain and discomfort.
Deer flies emerge in spring and remain active through early fall. Adult female deer flies lay eggs in masses of 100 to 1000. Egg masses are laid on foliage, rocks or in grass in moist soil. The LSU AgCenter provides detailed information on deer fly biology and management in Louisiana.
Bites from deer flies produce painful, raised welts that may bleed slightly. They transmit a rare bacterial disease known as rabbit fever (tularemia), though transmission is uncommon. Clean bites with soap and water, apply ice to reduce swelling, and use antihistamines to manage itching.
4. Stable Flies
Stable flies (Stomoxys calcitrans) closely resemble common house flies but possess a painful bite. These flies share some similarities with a housefly. One of its features is its proboscis, which it employs to puncture the skin of various animals including humans. They measure approximately 1/4 inch long and have a grayish body with dark stripes on the thorax.
Unlike other biting flies that slash skin, stable flies have piercing mouthparts that probe for blood vessels. Both male and female stable flies bite, typically targeting the ankles and lower legs of humans. The bites from stable flies can be quite painful and can cause discomfort for both livestock and people.
You’ll most commonly encounter stable flies during late summer and early fall. They’re most active during daylight hours and prefer sunny areas. To reduce stable fly populations around your property, promptly remove and properly dispose of animal waste, keep areas around livestock clean and dry, and eliminate decaying organic matter where larvae develop.
5. Black Flies
Black flies (Simuliidae family), also known as buffalo gnats or turkey gnats, are small but formidable biters. These annoying black flies, or “buffalo gnats”, are small, robust flies that pack quite a punch. These compact insects rarely exceed 1/8 inch in length but can appear in massive swarms during spring.
Black flies breed exclusively in running water, and larvae and pupae develop in flowing, typically non-polluted water. The immature stages develop in oxygenated water sources, therefore adults are usually associated with slow-moving streams, creeks, or rivers. This makes areas near Louisiana’s rivers and streams particularly prone to black fly activity.
Female black flies use blade-like mouthparts to create a small wound and feed on pooling blood. It is the female black flies that actually do all the biting, as they need the blood meal in order to develop their eggs. Their bites can cause a range of reactions in humans. Sometimes the puncture wound is small and a mere annoyance, while it can swell up to the size of a golf ball.
Certain people do have more severe reactions to these bites, referred to collectively as “black fly fever,” with symptoms including fever, nausea, headache, and swollen neck lymph nodes. Beyond biting, they will fly around people’s heads and try to sneak inside our mouth, nose, ears, and eyes.
Black fly season typically peaks in late spring, with these black flies tend to bite people throughout the late morning. Protection includes wearing light-colored, tightly woven clothing, using insect repellents containing DEET, and avoiding areas near flowing water during peak activity periods.
6. Sand Flies (Biting Midges / No-See-Ums)
Sand flies, more accurately called biting midges or no-see-ums (Ceratopogonidae family), are among the smallest and most frustrating biting flies in Louisiana. Since they rarely grow larger than 1/32 of an inch long, biting midges easily get into houses through window and door screens. Sandflies are common along the Gulf coast. Since they are so small – only 1/16th of an inch long, they became known as No-see-ums because the bite is obviously unpleasant and there appears to be no culprit.
These tiny flies have grayish bodies and wings that fold flat over their backs when at rest. All are associated with habitats in and around bodies of water, such as the mud or moist soil around streams, ponds, and marshes. Midges fly only during the warm months of the year and are most active before and during dusk.
Despite their minute size, no-see-um bites deliver disproportionate discomfort. Sand fly bites are very painful and produce intensely itchy welts that can persist for days or even weeks. The bites often appear in clusters where the insects have fed multiple times.
These biting flies can now be found in several southern and southwestern states, increasing the risk to the local population, including Louisiana. While sand flies transmit diseases to animals and humans, including a parasitic disease called leishmaniasis, leishmaniasis is rare in the United States according to the CDC.
To minimize no-see-um encounters, avoid outdoor activities during dawn and dusk, use fans to create air movement (their small size makes flying difficult in breezes), apply insect repellent to all exposed skin, and wear protective clothing with tight weaves.
7. Buffalo Gnats
Buffalo gnats is another common name for black flies (Simuliidae family), though the term is often used interchangeably with turkey gnats in Louisiana. These flies are also known as “buffalo gnats,” and the East Baton Rouge Parish’s Mosquito Abatement and Rodent Control department warned residents that they will be sticking around until the weather gets warmer.
These robust little flies get their buffalo gnat nickname from their distinctive humped thorax that resembles a buffalo’s back. They share all the characteristics and behaviors of black flies described earlier, including their tendency to swarm in large numbers during spring and their preference for flowing water as breeding sites.
Officials with the East Baton Rouge Parish’s Mosquito Abatement and Rodent Control Department said residents should expect black flies to be around until the weather becomes warmer. Department officials said the flies will try to crawl into people’s ears, noses and eyes. This behavior makes them particularly annoying despite their small size.
The most effective defense against buffalo gnats involves the same strategies used for black flies: protective clothing, DEET-based repellents applied to exposed skin and clothing, and avoiding outdoor activities near streams and rivers during peak emergence periods in spring. Spraying insecticide is ineffective for individual protection, making personal protective measures your best option.
8. Yellow Flies
Yellow flies (Diachlorus ferrugatus) are distinctive members of the horse fly family found primarily in the southeastern United States. The yellow fly is known in Florida as a fierce biter, and Louisiana residents encounter them in similar habitats. Yellow flies have yellowish bodies and the eyes are purplish-black with a green sheen.
These flies are similar in size and shape to deer flies, typically measuring 1/3 to 1/2 inch long. Yellow flies prefer shaded areas with both forests and bodies of water, making Louisiana’s wooded wetlands ideal habitat. They’re most active during hot summer months and prefer to bite in shaded areas rather than full sun.
Yellow flies are persistent and aggressive biters. A yellow fly bite results in localized swelling and itching that can be quite painful. Like their horse fly and deer fly relatives, they use scissor-like mouthparts to cut through skin and feed on pooling blood.
These flies are particularly troublesome for people working or recreating in forested areas near water. They tend to circle and dive at their targets before landing to bite. Protection strategies include wearing permethrin-treated clothing, applying DEET repellents to exposed skin, avoiding shaded areas near water during peak activity hours, and wearing long sleeves and pants when possible.
Understanding Louisiana’s biting fly species and their behaviors gives you the knowledge needed to protect yourself effectively. By combining habitat awareness, proper timing of outdoor activities, protective clothing, and appropriate repellents, you can significantly reduce your exposure to these persistent pests and enjoy Louisiana’s outdoors more comfortably throughout the year.
