Haematobia irritans

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Female, dorsal view. 
Adults horn flies appear very similar to stable flies, but are only about half the size. In feeding, the fly characteristically orients its head downward in contrast to the stable fly which usually directs its head upward.

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The horn fly, Haematobia irritans, found on the backs of cattle and to a lesser extent on horses, is about half the size of Stomoxys and has a relatively shorter proboscis. The palps are nearly long enough to reach the tip of the proboscis, in contrast to the stable fly.

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While feeding, the horn fly inserts and withdraws its proboscis repeatedly into the same puncture, in a pumping motion. Engorgement usually requires 4-10 min but feeding can take as long as 25-30 min.

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Horn flies are intermittent feeders and feed approximately 20-40 times per day. Females feed 1.5 times more frequently than males, with an average meal consisting of 0.5-1.7 mg of blood.

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Horn flies remain on cattle during the warmer seasons of the year, periodically biting their hosts and sucking blood. The fly leaves the host only to pass to another host, or to lay eggs when the cattle defaecates, or  when dislodged by means of the swish of the tail.

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Horn flies resting on the hump of a stanchioned Nellore male. 
Horn flies are found on parts of the body the host cannot reach with its head or tail - that is, the back between the head and shoulders, withers and backline, flanks and sides of abdomen, navel area, dewlap, and on the lower regions of the hind legs. During rain or on particularly hot, sunny days, they take refuge on the ventral abdomen.

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Horn flies resting on the flanks of a Holstein female. 
Horn flies apparently prefer dark colored areas of bicolored cattle, such as the black of the Holstein. However, such preference is influenced by ambient temperature.

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Life cycle. 
In ideal warm, humid weather, the entire cycle from egg to egg requires 2 weeks or less but may require a month or longer in dryer, cooler weather.

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Egg-laying female. 
Each female lays approximatelyb20 eggs at a time on freshly excreted cattle feces, leaving the host when dung is dropped. A female horn fly is capable of laying 400 eggs during its lifetime. The newly hatched  larvae undergo two molts reaching a third instar larvae in 3-12 days.

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Economic importance. 
The economic importance of blood loss by horn flies on cattle seems to be negligible, but they produce significant losses chiefly through irritation and annoyance resulting in disturbed feeding and improper digestion. The economic threshold  has not been clearly defined but infestations of 50-100 flies per animal are generally consedered to affect performance and are, therefore, economically damaging.