It’s shaping up to be a bad year for yellow flies.
Yellow fly, a common name for Diachlorus ferrugatus, is a tabanid in the family that also includes horse flies. There are more than 300 species of tabanids in North America, whose other common names include pine flies and deer flies.
Tabanid flies are among the most highly evolved insects, making them one of the most highly adapted animals on the planet.
All tabanids are fierce biters with slashing/sponging mouthparts adapted to consuming blood. The mouthparts feature a blade similar to a knife with a serrated edge. Because they are blood-feeders, they can transmit diseases such as tularemia and anthrax between prey animals. Some people develop allergic reactions to the bites, which swell and turn into nasty red sores.
Adult tabanids are swift, strong fliers and may travel more than a mile from their breeding areas. Most tabanids require a blood meal to develop eggs. However, they also feed on pollen, nectar, or honeydew excreted by sucking insects like aphids.
Adult tabanids are encountered in Florida between May and September. Most tabanids overwinter as larvae, form a cocoon and emerge during the spring and early summer. Most tabanid larvae develop in water, animal droppings or mud. The majority have a yearlong life cycle but some larger species may take two or three years to mature. Adult life span is 30 to 60 days.
Tabanids are ambush attackers that lie in wait in shady areas under bushes and trees for a chance to feed. They locate prey mainly by vision. Attacks occur during daylight, with peak activity beginning at sunrise and two hours before sunset.
They are drawn to moving objects, especially dark-colored ones, and are attracted to the color blue. There are no effective biological control programs for eliminating tabanids. Native insects including some dragonflies feed on them. They are also parasitized by wasp species that place paralyzed yellow flies in their nests as food for developing wasp larvae. The large burrowing sand wasps seen in late spring and early summer are among the most effective yellow fly predators and, although they have a hornet-like appearance, do not sting.
There is no known chemical method of control for yellow fly populations. Traps can be effective in small areas.
DEET, citronella and geranium oil are effective repellants. Ear tags and collars impregnated with pesticides help control attacks on animals. DEET, by the way, is extremely safe and allergic reactions to it are rare. If you are concerned, apply to your clothing, including a hat, instead of your skin.
For personal protection, avoid being outside around dusk and dawn. Use a repellant. Wear long pants and a long-sleeved shirt and choose light colors. Most tabanids tend to swarm around the highest point on their prey although yellow flies also attack the legs. There is evidence that wearing a tall hat will help discourage them from biting; it has been suggested the tall peaked hats depicted on crackers or hillbillies were worn to discourage tabanids.
Early Florida settlers used the leaves of beautyberry as a repellant for flies and other biting insects. They rubbed them on exposed skin and tucked them under the harness of horses, mules and oxen. Modern research has found this plant an effective insect repellant, and a commercial formulation is under development.
Several Franklin County residents have suggested ways to live with deer flies.
Gill and Lane Autrey drink a tablespoon of apple cider vinegar every morning, which they say acts as a natural repellant. This author has experimented with drinking cider vinegar and it does seem to discourage yellow flies.
Highly sensitive to yellow fly bites, Glynda Ratliff of St. George Island, has a suggestion for those who have already been bitten. As soon as possible, tape a slice of raw potato over the bite. Ratliff has found it significantly reduces her swelling.
The University of Florida has developed a “trolling fly trap” found to be highly effective in tabanid control. The trap is a blue cylinder mounted on a slow-moving object and coated with glue. The cylinder can be mounted on a lawnmower, four-wheeler, golf cart or a cap.
According to researchers, you can create an effective personal protection device by coating a blue plastic cup with tanglefoot, glue for trapping insects available in hardware stores. Mount the inverted cup on a blue ball cap and the flies will be more attracted to it than to the wearer. Flies drawn to you by the carbon dioxide you exhale will land on the cup and be trapped. Some people may find wearing such a device embarrassing.
A trap for the general area of outdoor activity can be made by painting a six-inch plastic flowerpot blue and coating in with tanglefoot. The pot must then be mounted on a moving object like a lawnmower or golf cart. This trap is only effective when in motion. Circling an area several times will reduce the number of yellow flies temporarily until more fly in from the surrounding area. The trap will not work if it sits in one place, even if it is rotating or shaking. Traps must be moved through space.
If you keep a trolling trap mounted on your lawnmower or golf cart, you will reduce fly numbers during their regular use. Deer flies usually fly at heights lower than 10 feet and usually attack the highest available area on the human body first. Walking with a trap mounted on a pole and shaken overhead can be effective.
Tanglefoot can be messy but can be readily removed with hand cleaners that contain citrus extracts. GoJo Natural Orange Pumice Hand Cleaner works very well.
A variation on the trap idea comes from getridofflies.com. Most tabinids are attracted to dark moving objects, and this fact can be used to kill them. To make a sticky black ball trap you will need following items: tough string; a medium sized ball; fly paper; a stool and tanglefoot.
Drill a hole through the seat of the stool and thread the string through it. Tie a knot in the cord above and below the seat of the stool so the cord doesn’t slide up and down on the string.
Apply a thick coating of tanglefoot to the ball. Attach the dark colored ball to the string and tie the open end of this string to the bottom of the stool. Next, wrap the fly paper over the legs of the stool. After this, hang the stool in the area where you have yellow fly infestation (preferably an open area).
Due to wind movement the ball starts swinging in air. The swinging motion of the dark colored ball will attract the yellow flies. When they come near the trap, they try to land on it and get stuck on the fly paper or the ball.