Texas is home to over 100 species of biting flies, ranging from large horse flies that leave painful, bleeding wounds to tiny biting midges you can barely see. Which species you’ll encounter depends on where you are in the state, the time of year, and how close you are to water. Here’s what to know about identifying them, avoiding bites, and treating the ones you don’t dodge.
Horse Flies and Deer Flies
These are the big, aggressive biters most Texans think of first. Texas has 52 species of horse flies and 33 species of deer flies, and they’re found statewide near creeks, ponds, marshes, and wooded areas.
Horse flies range from about 3/8 inch to just over an inch long. Some are solid black, while others have colored patterns on their abdomens and wings. Deer flies are smaller (1/4 to 1/2 inch), typically black to brown with yellowish markings, and have distinctive banded wings with dark patterns. Both species are daytime feeders, and they locate hosts by sight, which is why they’re drawn to movement, dark colors, and the carbon dioxide you exhale.
Unlike mosquitoes, which pierce the skin with a needle-like mouthpart, horse flies and deer flies use blade-like jaws to slice the skin open and lap up the pooling blood. That’s why their bites hurt immediately, often bleed, and tend to swell more than a typical insect bite. They’re most active in late spring through summer, with peak activity during the hottest months. Both can mechanically transmit equine infectious anemia to horses, which makes them a significant livestock concern in rural Texas.
Stable Flies
Stable flies look almost identical to common house flies, with one key difference: a bayonet-like mouthpart that protrudes forward from under the head. If a “house fly” is biting your ankles and lower legs, it’s almost certainly a stable fly. They breed in decaying organic matter like wet hay, grass clippings, and livestock manure, making them a persistent problem around farms, ranches, and even suburban yards with compost piles.
Unlike horse flies, stable flies tend to peak in cooler weather. In the Gulf Coast region, populations build in late fall and can peak in early winter. They’re daytime biters and prefer to feed on the legs, which is why cattle will often stand in water to escape them. For people, stable fly bites typically show up as small red welts on the ankles and shins.
Biting Midges (No-See-Ums)
Along the Texas coast and near inland bodies of water, biting midges are the flies you feel but can’t find. These tiny insects, often called no-see-ums or punkies, are small enough to pass through standard window screens. Females need blood meals to produce eggs and will readily bite humans, leaving itchy red welts that can be disproportionately irritating for their size.
Biting midges breed in salt marshes, mudflats, and wet soil around water. Decaying seaweed tossed onto beaches after storms creates ideal breeding habitat, which is why coastal areas can see sudden population spikes after rough weather. They’re most active around sunrise and sunset, and they avoid even slight breezes. If you’re at a beach house and the wind dies down at dusk, that’s peak no-see-um time. Summer months bring the highest populations, but they can bite any time of year in Texas’s mild climate.
Biting midges can transmit vesicular stomatitis virus to livestock, though human disease transmission from these flies in Texas is rare.
Black Flies
Black flies (sometimes called buffalo gnats) are small, humpbacked flies that breed in flowing water. In Texas, they’re most common near rivers and streams, particularly in the Hill Country and East Texas. They’re most prevalent in early to late spring, and like horse flies, they feed during daylight hours. Their bites often produce a disproportionate reaction: significant swelling, itching, and sometimes a small blood blister at the bite site. In livestock, large swarms of black flies can cause serious distress, and they’re known to transmit vesicular stomatitis virus.
When Biting Flies Are Most Active
Texas’s warm climate means biting flies can be active across a longer stretch of the year than in northern states, but each species has its own peak:
- Horse flies and deer flies: Late spring through summer, most intense on hot, humid, still days.
- Black flies: Early spring through late spring, near flowing water.
- Stable flies: Late fall into early winter along the Gulf Coast, though present year-round in areas with livestock.
- Biting midges: Summer peak, but active year-round in coastal areas. Worst at dawn and dusk in calm air.
All biting flies are more active in still air. A breeze of even a few miles per hour dramatically reduces biting midge activity, and it makes it harder for larger flies to home in on a target. This is why screened porches with fans, or simply sitting in a breezy spot, can make a real difference.
What Actually Works for Prevention
Here’s the frustrating truth about repellents and biting flies: DEET, the gold standard for mosquito protection, works well against biting midges and black flies but doesn’t work well against horse flies, deer flies, or greenheads. No commercially available repellent reliably deters those larger species. Picaridin performs similarly to DEET for mosquitoes and smaller biting flies, and products with low concentrations are labeled for biting flies and chiggers. Natural oil-based repellents, including oil of lemon eucalyptus, are less effective than DEET or picaridin across the board and lose effectiveness quickly after application.
For horse flies and deer flies, physical barriers and traps work better than sprays. Long sleeves and pants in light colors help, since these flies are attracted to dark objects. One particularly effective tool is the “trolling deer fly trap,” developed at the University of Florida: an inverted six-inch plastic nursery pot painted bright blue and coated with a sticky adhesive like Tanglefoot. Mounted on a slow-moving vehicle like a riding mower, the trap exploits the flies’ attraction to movement and dark, contrasting objects. A sticky black ball hung from a tree branch in a windy spot works on the same principle.
For biting midges, fine-mesh screens (smaller than standard window screen) on windows and porches can keep them out of living spaces. Fans aimed at seating areas create enough air movement to keep them away.
Reducing breeding habitat matters too. Stable fly populations drop when you eliminate wet, decaying organic matter: old hay, grass clippings left in piles, and accumulated manure. Biting midges breed in standing water and wet soil, so drainage improvements around a property can help in some cases.
Treating Bites and Spotting Infections
Most biting fly wounds heal on their own within a few days. Wash the bite with soap and water as soon as possible to lower infection risk. An ice pack wrapped in cloth, applied for at least 20 minutes, helps with swelling. Keeping the area elevated, when practical, also reduces swelling. Over-the-counter anti-inflammatory pain relievers handle the pain, and an antihistamine can take the edge off itching.
The main risk with any biting fly wound is secondary bacterial infection, because the flies create an open wound rather than a tiny puncture. Watch for these signs of infection in the days after a bite: fever or chills, spreading redness or red streaks around the bite, a fluid-filled blister forming at the site, skin that feels warmer than the surrounding area, pus or drainage, swollen lymph nodes near the bite, or unusual fatigue. An infected bite needs antibiotics, so don’t wait on these symptoms.
Horse fly bites in particular tend to bleed freely and swell more than you’d expect. This is normal. Their mouthparts release compounds that prevent clotting, which is why the wound keeps oozing. Firm pressure with a clean cloth stops the bleeding, and the swelling typically peaks within a few hours before gradually subsiding.