Yellow flies are biting flies known for their painful bite. They are typically ¼ to ½ inch in size, with yellowish bodies and bright green or golden eyes. While multiple species are called “yellow flies,” Diachlorus ferrugatus is the true yellow fly in Florida and a significant pest in the southeastern United States. Female yellow flies require a blood meal to produce eggs, similar to mosquitoes.
Attraction Through Chemical and Thermal Cues
Yellow flies locate potential hosts by detecting specific chemical and thermal signals. Carbon dioxide (CO2), exhaled by humans and other warm-blooded animals, is a significant long-range attractant for these flies. They possess specialized olfactory receptors that allow them to detect changes in CO2 concentrations, guiding them toward a source. This allows them to pinpoint hosts from a distance.
Body heat is another important cue that yellow flies use to find their targets. Warm bodies emit thermal radiation, which these flies can sense. This thermal signature helps them distinguish living hosts from their surroundings. Moisture, such as sweat on the skin, also acts as a chemical attractant.
Visual Signals and Movement
Beyond chemical and thermal cues, yellow flies are strongly influenced by visual signals. They are particularly attracted to dark, moving objects. Dark colors absorb more light and heat, making them appear more prominent and attractive to these flies. This preference is evident in various trapping methods that utilize dark objects to lure the flies.
Movement serves as a direct indicator of a living host. Even slight movements can signal the presence of a potential blood meal. The combination of a dark visual target and motion mimics a large animal, making it a strong attractant. This explains why individuals walking or moving in shaded, infested areas often experience more bites.
Habitat and Activity Patterns
Yellow flies prefer specific environmental conditions that provide both breeding grounds and ample opportunities for host seeking. They are commonly found in wooded areas, swamps, marshes, and humid environments, especially near bodies of water like rivers, creeks, and ponds. These habitats offer the moisture and shaded conditions conducive to their larval development.
Understanding their preferred environment helps predict where encounters are most likely. Yellow flies are most active during daylight hours. They exhibit increased aggression in the late afternoon and on cloudy, humid days. Their activity is reduced in direct sunlight or strong winds, making shaded, still areas their prime hunting grounds.