Stable flies, which used to be found only in confined animal areas such as feedlots and barns, are now being found on cattle in pastures, according to a Kansas State University Research and Extension livestock entomologist.
"The current methods of feeding hay in pastures are creating a new habitat for stable flies," says Alberto Broce, K-State livestock entomologist who studies fly populations. "These methods are very wasteful. Cattle can waste up to 45 percent of the hay in round bale feeders, which then gets mixed with manure on the ground and creates a suitable habitat for stable flies."
There is no effective chemical treatment for pastured cattle against stable flies because any applied insecticides are easily removed from the animals’ legs by vegetation and dew. Producers can reduce the number of stable flies in pastures by frequently moving hay feeders to new sites and removing manure and hay from the old feeding sites soon afterwards.
Stable flies feed mostly on the legs of their host and can cause up to a half pound reduction in weight gain per calf or cow each day, Broce says. Cattle will react to the flies by stamping their feet, switching their tails, tucking legs under their bodies and remaining in water for extended periods of time.
Stable flies colonize the manure and wasted-hay mixtures of winter feeding sites in early spring and will maintain their largest population levels for six to eight weeks during May and June. Stable fly populations crash in July and August due to high temperatures and drier weather, but will reach a second peak during September and October.
In late May 2007, traps placed in pastures near Manhattan averaged up to 255 stable flies per trap each day, he said. In mid-July, those same traps were only catching about two flies per day.