These estimates do not include the large drop of blood that is usually left at the side of each bite. Their intermittent feeding makes them ideal for the mechanical transmission of disease-causing pathogens. A fly interrupted during its feeding may pass readily to another animal so that both sick and healthy animals may be fed on in succession by the same fly. Anaplasmosis, anthrax, tularemia and several other diseases are known to be spread by these vicious bloodsuckers. Back To Top Control Control of horse flies and deer flies is very difficult.
Insecticides are usually ineffective since the insects spend little time on the animals.
Insecticide treatment of breeding areas is also impractical. Several factors have been suggested to explain the difficulties of controlling horse flies in field situations where it is not feasible to handle the animals on a frequent schedule. Some degree of repellency can be obtained for two or three days after applying a spray mixture of pyrethrins and piperonyl butoxide. Use of this mixture may benefit dairymen or small herd owners in areas of heavy local infestation. Insecticides currently registered on cattle only afford moderate control of horse flies at best.