Pestipedia

Yellow Flies

**Yellow Flies** (*Diachlorus ferox*) are biting horse flies, a blood-feeding pest of humans and livestock common in the southeastern US. The conflict is **blood loss and extreme nuisance**: the female fly has razor-sharp, blade-like mouthparts that slice the skin to feed on blood. Their bite is **extremely painful**, and they attack persistently in large numbers, often targeting the head and shoulders, driving people and animals indoors during the summer months.

Taxonomy and Classification

Yellow Flies belong to the Order Diptera (True Flies) and the Family Tabanidae (Horse Flies and Deer Flies). They undergo complete metamorphosis.

Physical Description

Adults are medium-sized, 8 mm to 10 mm long.

  • **Adult (Key ID):** Brownish-yellow body; bright **green eyes** (often iridescent); smoky or cloudy wings; they fly quickly and land silently on the host before biting.
  • **Larva (Key ID):** Aquatic or semi-aquatic maggot found in wet, muddy organic soil.
  • **Damage ID (Key):** Painful, bleeding wounds (females cut the skin rather than piercing it); severe annoyance during outdoor activity.
  • **Conflict:** Public Health (Biting Nuisance).

Distribution and Habitat

Found primarily in the southeastern coastal plains of the US, especially near swampy or marshy areas. Habitat is wooded areas and open spaces near larval development sites.

Behavior and Conflict

The conflict is their persistence and painful bite.

  • **Blood Requirement:** Only the female bites, requiring a blood meal to produce eggs.
  • **CO2 Tracking:** They are highly attracted to moving objects, carbon dioxide, and dark colors.

Management and Prevention

Management is **Exclusion and Mechanical Control**.

  • **Mechanical Control (Key):**
    • **Trapping:** Using specialized, large **black ball traps** (or horse-fly traps) coated with an adhesive to capture the flies attracted to the dark color and movement.
    • **Repellents:** Use of highly concentrated DEET or picaridin repellents on exposed skin.

    • Conservation and Research

    Research focuses on refining the chemical and visual attractants used in large-scale fly trapping programs to reduce populations near recreation areas and livestock.