September 2002

Dog Flies and Their Control

            When fall comes to our area, those refreshing weather fronts will move through from the north bringing lower humidity, lower temperatures and the infamous dog fly. The stable fly, known as the dog fly in northwest Florida, is a blood feeding fly that is a nuisance to man, pets, and livestock.

            From August through November the dog fly congregates on the Florida Panhandle beaches. This fly originates from farming areas in southern Alabama, Mississippi, Georgia and northern Florida and rides the northerly winds associated with cold fronts that move through our area.

            Stable or dog flies look like house flies in size and color. The dog fly, however, has a long piercing mouthpart to penetrate the skin and obtain blood, the house fly does not. Both sexes of the dog fly feed on blood, usually twice a day. The life cycle is egg to larva to pupa to adult, complete metamorphosis. The female lays 500 – 600 eggs in her lifetime, they hatch in 2 to 3 days, feeds in the larval stage for 2 to 4 weeks, then into the pupal stage where it transforms into an adult in 1 to 4 weeks. Adults live for 2 to 3 weeks, depending on weather conditions. Adults can be carried by winds up to 150 miles from where they were born and can be produced in Florida year-round because of our mild climate.

            Their eggs are laid on decaying, wet, organic matter such as manure, rotting grain, silage or a mixture of such, usually found around livestock or dairy farms, hence the name, stable fly. The adults feed on the legs and bellies of cattle and horses and also dog’s ears, hence the name dog fly. This fly prefers animals and feeds on man only if there are no animals around. Dog flies are inactive at night, resting in vegetation. As the sun rises and warms things up, the flies become active, primarily using sight to find its host.

            The most practical and economical method for controlling stable/dog flies is to eliminate their larval habitat. Decaying, wet organic matter (manure or compost piles) must be spread out and dried, maggots cannot develop in dry materials. If this is not feasible the rotting material can be covered with black polyethylene plastic and allowed to compost. The plastic cover excludes the flies from laying their eggs. Natural predators such as chickens and parasitic wasps destroy many flies while in their larval stage. Once they reach the adult stage, sticky traps, fly strips, chemical pesticides and repellents are our only defense.

            Because of the tremendous impact that the dog fly has on tourism in Florida, the State has funded a special Dog Fly Control Program since 1972. The program is administered through the Department of Agriculture and Consumer Services and consists of an aerial spray (adulticiding) program. A DC-3 aircraft dispenses the insecticide naled (Dibrom) from an altitude of about 150 feet, along the beaches, usually in the late morning when the flies become active. Aerial spraying is initiated when landing rate counts of more than 5 flies per minute are recorded by trained personnel provided by local mosquito control agencies.

            Another option to counteract this pest is the use of repellents. Commercial repellents containing 25–40% DEET (diethyl metatoluamide) have been reported by Consumer Reports to have kept stable/dog flies at bay for at least 2-5 hours. The use of long sleeve shirts, pants, thick socks and a head net are effective also, but if you are going to the beach to sun bath or swim you would need repellents.

            In summary, effective control can be obtained at the source, through prevention, however, once in the adult stage, adulticiding with pesticides has only temporary effectiveness even if application timing and environmental conditions are ideal, new adult populations continually move in with northerly winds. Repellents work but only for a couple of hours before they need to be reapplied. Physical barriers such as clothing may be impractical, especially if it is warm. The best control seems to be cooler temperatures. When the temperature falls below 60°F the flies may be present but their activity drops off appreciably, to the point where they may land but don’t bite.