Flies should not only be viewed as pests. It is above all problematic that both stable flies and autumn flies (big-headed flies, horn flies, horse flies) can carry and transfer numerous viral, bacterial and parasitic illnesses to animals. Output losses are the consequence of large fly loads. When the temperatures rise in spring, prompt and sufficient control must follow. Otherwise an all-year-round problem can quickly develop. Preventative and consistent fly combating measures are important corner marks of an operational hygiene programme and should, above all, from an economic point of view, not be ignored.