Yellow flies, scientifically known as Diachlorus ferrugatus, are notorious biting insects, especially prevalent in regions like Florida. Similar to mosquitoes, it’s the female yellow fly that bites, as they require blood for egg production. Male yellow flies, on the other hand, primarily feed on pollen and nectar. These flies are most commonly encountered during the hot summer and early fall months, with peak activity from April through June, and they can remain present until November.
Adult yellow flies are characterized by their predominantly yellowish color and a size of approximately 1 to 1.2 cm in length. Their front pair of legs are distinctively black, while the other legs exhibit a yellowish-gray hue. The wings are transparent, featuring a black stigma and brown or tan patches near the wing apex. This wing pattern is a key differentiator from deer flies, which have similar patches across the middle of their wings.
Yellow flies possess a striking appearance with a black-striped, yellow furry abdomen and brilliant blue-green eyes. In some species, the yellow abdomen may also feature a black-haired lining along the sides, accompanied by a broad yellow stripe down the middle.
Yellow fly close up. Image courtesy of Canva.
The Painful Bite of the Yellow Fly
The female yellow fly is considered a significant biting pest in areas where they are found. They are known to aggressively attack humans, and their bites are notably painful, often resulting in substantial, itchy swellings. If not properly cleaned and treated with antiseptic ointment, these bites can become infected. Preventing yellow fly bites can be challenging due to their rapid flight and tendency to bite any exposed skin. While they may bite at any time of day, they are most active in the late afternoon and on cloudy days.
Unlike mosquitoes, yellow flies do not inject an anesthetic when they bite, which accounts for the sharp pain associated with their bites. They use serrated mouthparts to puncture the skin, creating a jagged cut before feeding on blood through their tube-like proboscis.
Boy with yellow fly bite. Image courtesy of Canva.
Yellow Fly Behavior and Habitat
Yellow flies are diurnal feeders, meaning they are active during the day and retreat to wooded areas to rest at dusk. Their peak activity times are typically late afternoon and cloudy days. They are particularly abundant near freshwater sources and in wooded or shaded environments.
These pests are less likely to enter homes but are frequently found around water bodies such as pools and ponds. Homeowners with standing water on their property are more prone to encountering yellow flies. These flies are most bothersome in late summer and early fall. Avoiding direct sunlight, they appear in large numbers on overcast days and during the later hours of the day.
Effective Yellow Fly Control Methods
Yellow flies are attracted to dark shapes and movement. This behavior can be exploited for trapping purposes. One effective method involves hanging inflatable black balls coated with a sticky adhesive in your yard. The flies are drawn to the movement and dark color, becoming trapped when they land on the sticky surface. Over time, this can significantly reduce the local yellow fly population.
Yellow fly ball trap. Image taken on site at SWCMCD.
Certain insecticides have proven effective against the larval stages of yellow flies. Chemicals such as Permethrin, Carbaryl, and Malathion can be applied in infested areas to provide temporary relief. These products are commonly available at farm supply and hardware stores. However, chemical control may only offer short-term solutions due to the continuous influx of yellow flies from surrounding areas, as they are strong fliers capable of traveling 1-2 miles from their breeding sites in search of a blood meal.
Using insecticides at yellow fly development sites is generally not recommended, as these wet habitats often support other aquatic life that could be harmed by chemical treatments.
Vegetation management is another approach to yellow fly control. Since yellow flies prefer shaded areas and avoid sunny, open spaces, removing shrubs and small trees around your home can increase sunlight exposure. This makes the environment less appealing to yellow flies and helps to naturally deter them.
Map of South Walton Area Outlined in Red.
In conclusion, understanding yellow fly behavior, habitat, and effective control methods is crucial for minimizing their impact. By implementing a combination of trapping, vegetation management, and judicious use of insecticides, you can reduce yellow fly populations and protect yourself from their painful bites.
