How to Identify and Control 6 Dangerous Biting Flies in Texas

Texas hosts some of the most aggressive biting flies in North America, with populations reaching record highs due to increased rainfall patterns.

Recent reports indicate horse fly infestations are “higher than normal” and represent “the worst year” some experts have experienced in over a decade.

Whether you’re hiking East Texas trails, working on a ranch, or simply enjoying your backyard, understanding these six dangerous species will protect you from painful bites and potential disease transmission.

You’ll discover species-specific identification markers, peak activity periods, and proven protection strategies that actually work against Texas’s most problematic biters.

This guide covers the flies most likely to target you throughout the year, giving you practical defense tactics for each encounter.

Horse Flies: Texas’s Most Aggressive Biters

Horse flies represent the largest and most painful threat among Texas biting flies. Over 100 species of horse flies are known to occur in Texas, making proper identification crucial for effective control.

Key Identification Features:

• Size: ¾ to 1¼ inches long
• Large, prominent eyes with metallic coloring
• Dark gray to black bodies
• Silent flight approach
• Active during hot, sunny days

Horse flies deliver the most painful bite of any Texas fly species. Their razor-sharp mandibles cut through skin rather than pierce it, creating wounds that bleed freely and attract more flies to the area.

Peak Activity and Behavior: These aggressive hunters are most active from May through September during the hottest parts of the day.

They’re particularly drawn to movement, dark clothing, and carbon dioxide emissions. Horse flies actively hunt for their next blood meal, making them relentless pursuers once they’ve targeted you.

Pro Tip: Horse flies cannot hover like other species – they must land to bite. Quick movement and swatting are more effective against horse flies than against smaller biting species.

Targeted Control Methods:

• Use sticky traps positioned 3-4 feet high in sunny areas
• Apply permethrin-treated clothing for reliable protection
• Install fans on porches and patios – horse flies struggle in moving air
• Eliminate standing water sources where larvae develop

Deer Flies: The Persistent Head Hunters

Deer flies earn their reputation as relentless head and neck attackers throughout Texas. 33 species of deer flies (Chrysops spp.) range from 1/4 to ½ inch long, typically appearing smaller than horse flies but equally determined.

Distinctive Characteristics:

• Size: ¼ to ½ inch length
• Banded or spotted wings with dark patterns
• Golden-yellow eyes with distinct patterns
• Prefer attacking head, neck, and shoulders
• Circle targets before attacking

Unlike horse flies that attack exposed skin anywhere on the body, deer flies show a marked preference for the head and neck region.

They often circle potential victims multiple times before landing, creating that familiar buzzing sound around your ears.

Common Mistake: Many people assume deer flies are less dangerous because they’re smaller than horse flies. However, deer flies are actually more persistent and likely to successfully bite due to their focused targeting behavior.

Habitat and Timing: Deer flies thrive near wooded areas, marshes, and streams throughout Texas. Peak activity occurs from late spring through early fall, with the highest populations during humid, overcast days when temperatures range from 70-85°F.

Specialized Protection Strategies:

• Wear light-colored head coverings – deer flies are attracted to dark colors
• Use insect head nets in heavily infested areas
• Apply repellents specifically to head, neck, and shoulder areas
• Avoid wooded trails during peak morning hours (8-11 AM)

Key Takeaway: Deer flies have limited flight range. Moving 100-200 yards from their breeding habitat often provides complete relief from attacks.

Black Flies: The Daylight Swarmers

Black flies pose unique challenges in Texas due to their daytime feeding behavior and swarming tendencies. Adult flies are small (1-5 mm) with a characteristic arched or humped back giving rise to the common name “buffalo gnat”.

Recognition Features:

• Very small size (1-5 mm)
• Distinctive humped back appearance
• Dark gray to black coloration
• Swarm in large numbers
• Most active during daylight hours

Recent outbreaks show black flies “biting people during the day – particularly around the neck and head, and leaving persistently itchy swollen areas”.

Their saliva contains anticoagulants that prevent blood clotting, leading to prolonged bleeding and intense itching.

Behavioral Patterns: Black flies differ significantly from mosquitoes in their feeding behavior. While mosquitoes are most active at dawn and dusk, black flies attack throughout daylight hours, with peak activity occurring during warm, humid mornings.

Environmental Preferences:
These flies breed exclusively in flowing water sources – streams, rivers, and artificial water features with current. This Texas fly “loves the heat and moving water”, making areas near running water particularly problematic during summer months.

Multi-Layer Defense Approach:

• Schedule outdoor activities for early morning or evening hours
• Use DEET-based repellents on exposed skin
• Burn citronella torches or coils to create smoke barriers
• Wear long sleeves and pants during peak activity periods

Stable Flies: The Ankle Biters

Stable flies target the lower legs and ankles, earning their nickname as “ankle biters.” These flies are particularly problematic around livestock areas, kennels, and properties with organic debris accumulation.

Physical Identification:

• Size: ¼ inch long
• Gray coloration with dark stripes on thorax
• Forward-pointing proboscis (needle-like mouthpart)
• Similar appearance to house flies but with biting mouthparts
• Strong, direct flight patterns

Stable flies inflict sharp, needle-like bites that create immediate, intense pain. Unlike other biting flies that may bite multiple times, stable flies typically bite once and move to a new location.

Breeding and Development: These flies develop in decomposing organic matter including:

• Livestock manure mixed with bedding
• Grass clippings and compost piles
• Dog waste accumulations
• Wet, rotting vegetation

Habitat Modification Strategies:

• Remove or frequently turn compost piles
• Clean up pet waste immediately
• Eliminate wet, decaying vegetation near structures
• Store livestock feed in sealed containers
• Maintain dry conditions around animal housing

Protection Tactics:

• Wear closed-toe shoes and socks when walking through grass
• Apply repellents to lower legs and ankles specifically
• Use fans in outdoor seating areas – stable flies avoid windy conditions
• Install fine-mesh screens on porches and patios

Biting Midges (No-See-Ums): The Invisible Threat

Biting midges, commonly called no-see-ums, present unique challenges due to their microscopic size and ability to penetrate standard screens. No-see-ums bites create discomfort, and scratching “can lead to infection”.

Size and Appearance:

• Extremely small: 1-3 mm (barely visible to naked eye)
• Gray to black coloration
• Fuzzy or hairy appearance under magnification
• Weak flight capability in windy conditions
• Most active during calm, humid conditions

Bite Characteristics and Treatment: No-see-um bites appear as “a little cluster of red bumps” that are “more intense” than mosquito bites. The intense itching can persist for days or weeks if not properly treated.

Immediate Treatment Protocol:

• Apply ice or cold compress for 10-minute intervals
• Use over-the-counter antihistamine cream
• Avoid scratching to prevent secondary infection
• Consider oral antihistamines for severe reactions

Specialized Prevention Methods: Unfortunately, “biting midges are so tiny they can get through window and door screens”, requiring additional protective measures:

• Install ultra-fine mesh screens (18×16 mesh or finer)
• Use permethrin-treated netting around outdoor seating
• Apply repellents containing picaridin or oil of lemon eucalyptus
• Keep “windows and doors closed when they are active”

Timing and Weather Patterns: No-see-ums are most active during:

• Dawn and dusk hours
• Calm, humid evenings
• After rainfall when humidity is high
• Areas near standing or slow-moving water

Sand Flies: The Disease Carriers

Sand flies pose the most serious health threat among Texas biting flies due to their ability to transmit leishmaniasis.

Texas is “the only state in the U.S. required to report Leishmaniasis cases”, highlighting the significance of this threat.

Health Risk Assessment: Recent data shows Texas reporting “around 11 and nine cases” of leishmaniasis in recent years, with numbers becoming “more consistently” reported. While not extremely common, the potential for serious illness makes sand fly prevention critical.

Physical Description:

• Size: 2-3 mm long
• Tan to light brown coloration
• Extremely hairy or fuzzy appearance
• Weak, hopping flight pattern
• Prefer protected, humid microenvironments

High-Risk Areas in Texas:

• South and Southwest Texas regions
• Areas near the Mexican border
• Desert and semi-arid environments
• Rocky outcropping and cave entrances
• Abandoned structures and debris piles

Medical Prevention Protocol:

• Seek immediate medical attention for persistent, non-healing bite wounds
• Document bite locations with photos for medical reference
• Report suspected sand fly encounters to local health authorities
• Use maximum-strength DEET repellents in high-risk areas

Environmental Management:

• Remove brush piles and debris near structures
• Seal cracks in foundations and exterior walls
• Install tight-fitting screens on all openings
• Eliminate organic matter accumulation around buildings

Pro Tip: Sand flies cannot jump or fly more than a few feet high. Sleeping or resting areas elevated 6+ feet above ground level significantly reduce exposure risk.

Universal Protection Strategies for All Texas Biting Flies

Clothing-Based Defense: Wear “light colored clothing” as “black flies are attracted to dark colors” and “long sleeves, pants and hat, covering as much exposed skin as possible” since most biting flies cannot bite through fabric.

Repellent Application Guidelines:

• DEET: Most effective against all species, 20-30% concentration recommended
• Picaridin: Less odor than DEET, equally effective against most species
• Oil of lemon eucalyptus: Natural alternative, requires frequent reapplication
• Permethrin: Treat clothing and gear, not for direct skin application

Timing and Activity Modification: Avoid “peak biting times” and remember that “unlike mosquitoes, black flies are daytime feeders”. Plan outdoor activities during:

• Early morning hours (before 8 AM)
• Late evening (after 7 PM)
• Windy days when flight is impaired
• Cooler temperature periods

Environmental Controls:

• Eliminate standing water sources within 200 yards of living areas
• Maintain air movement with fans in outdoor spaces
• Remove organic debris and compost from immediate vicinity
• Install and maintain proper screening on all openings

Emergency Bite Treatment: For all biting fly encounters:

1. Clean bite area immediately with soap and water
2. Apply cold compress to reduce swelling and pain
3. Use topical antihistamine or hydrocortisone cream
4. Monitor for signs of infection or allergic reactions
5. Seek medical attention for severe reactions or suspected disease transmission

Common Mistake: Many people apply repellents only to exposed skin. Clothing treated with permethrin provides “tested and proven defense against biting flies” and should be part of any comprehensive protection strategy.

By understanding the specific behaviors, habitats, and control methods for each of these six dangerous biting fly species, you can significantly reduce your risk of painful encounters while enjoying Texas’s outdoor spaces.

Remember that integrated pest management combining multiple strategies always provides the most effective long-term control.

Key Takeaway: Different biting fly species require different approaches. Generic “bug spray” rarely provides adequate protection against Texas’s diverse and aggressive biting fly populations.

Species-specific strategies, combined with environmental management, offer your best defense against these persistent pests.