Stable flies are blood suckers that look much like house flies, except that they have piercing-mouthparts, which jut out like bayonets from the front of their heads. These insects visit cattle and horses only to feed. They spend the rest of their time resting on walls, rafters, ceilings, or vegetation. When feeding, stable flies orient themselves with their heads pointing upward. They prefer to feed low on animals, usually on the lower parts of legs or flanks. Both sexes feed on warm-blooded animals, including horses, cattle, hogs, and man. The bite of the stable fly is so painful that cattle will stamp or kick trying to rid themselves of these pests. Studies have shown that heavy stable fly infestations of 50 or more per animal will reduce feed efficiency by 10 to 13 percent.
Stable flies are usually found in dairy or feed lot operations. They prefer to breed in a mixture of rotting or fermenting straw and manure, or other types of rotting and fermenting vegetable matter. Stable flies are becoming pasture pests in areas where round bales are used extensively. These flies are able to develop as larvae in the rotted hay at the base of improperly stored large hay bales. Each stable fly female produces about 500 eggs, and it takes from 20 to 60 days for them to complete their life cycle.
It is difficult to control stable flies by applying insecticide onto animals because the flies usually feed on the lower portion of their legs. Sprays are not satisfactory since they are easily washed off the legs when the cattle walk through water or wet grass. Space sprays (foggers) or residual sprays can help reduce numbers, but breeding site elimination is the most effective means of control.
By Lee Townsend, Extension Entomologist