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Horn Flies

Horn Flies
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Horn flies are small (3/16 inch long), dark gray flies that feed on cattle and occasionally horses. Both sexes are blood feeders, can have up to 20 or more blood meals each day using their stiff needle-like mouthparts. Irritations from the bites annoy animals and occasionally, the wounds may become infected. Horn flies stay on animals almost continuously. During extremely hot weather or rains, they will move the underside of the animal. They fly up in swarms when disturbed but soon return to an animal. Females leave only to deposit their eggs on manure within about 10 minutes of it hitting the ground.

Horn fly maggots only develop in cattle manure and do best in the grass manure of pastures not Barns because few flies emerge from droppings of cattle on concentrated feed (in other words grain). The life cycle is completed in 10 to 14 days. Each female can lay up to 500 eggs so very large populations can build up in one summer. Winter is spent in the pupal stage beneath manure pads or in the soil, adults in late May. Without some type of prevention like fly tape, every animal in a herd may have several hundred horn flies by mid- to late summer. Bulls usually carry the heaviest infestations.