EN
High populations of various insect species, especially common in the summer, may adversely affect farm animal health because of the transmission of contagious and parasitic diseases and the induction of insect allergies. Blood-sucking insects may compromise animal welfare and cause economic losses due to the annoyance and distress suffered by the animals, feeding interruptions and energy requirements for avoidance or defense behaviours initiated by the animals in response to the insects. Consequently, significant decreases in production traits, such as weight gain in beef cattle or milk yield in dairy cattle, can be expected when blood-sucking insects are numerous.There are several globally distributed families of Diptera that harass farm animals; these include the Culicidae, Ceratopogonidae, Muscidae, Oestridae, Simuliidae and Tabanidae. Large insect populations gains problems because of a lack of effective and long-lasting repellents and of the difficulty or impossibility to apply available compounds, e.g., on remote pasture areas or in freeroaming herds. Described are consequences caused by insect harassment of grazing farm animals and the main behavioral strategies used by the animals to cope with this harassment.