The body is about 3/16 of an inch long, or about half the size of the common house fly.


Adult horn flies have dark, shiny bodies with somewhat overlapping wings covering the abdomen. The head features small, brownish-red, downward-pointing antennae, and the thorax is striped on top.

Horn flies received this name due to their habit of clustering around the horns of cattle, although they typically prefer to settle on the backs of cattle during the cooler parts of the day and on the belly during the hotter part of the day. They have been known to feed on horses, dogs, swine and sometimes humans. However, they have a well-documented close association with cattle and typically remain on or near cattle throughout their entire life cycle

Horn flies stay on animals almost continuously. They characteristically rest with their heads pointing toward the ground and their wings held at a 45 to 60 degree angle to their bodies. During extremely hot weather or rains, they will move lower sides and 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.

Feed on cattle and occasionally horses. Both sexes are blood feeders, taking 20 or more blood meals each day with their stiff needle-like mouthparts. Irritations from the bites annoy animals and occasionally, the wounds may become infected.

Horn flies have been implemented as a developmental vector (carrier) for Stephanofilariastilesi, a spirurid nematode that causes stephanofilariasis in cattle. Stephanofilariasis is a granular dermatitis that occurs mainly on the belly, scrotum, prepuce and udder of cattle in the western United States Horn flies are one of the most important cattle pests, causing over $1 billion in economic losses each year. Damage and health-related effects of horn flies include:
  • Loss of milk production and weight gain in dairy and beef cattle
  • Damage to cattle hides resulting in poor quality leather.
Irritations from the bites annoy animals and occasionally, the wounds may become infected.
Horn fly Prevention Tips
The most effective way to control horn fly populations is to take an integrated pest management approach to both the adults and larvae. The horn fly’s ability to thrive allows for large densities in a small amount of time and just treating for the adults will not decrease the infestation. The best approach is to use several methods at once, focusing on source reduction.

Three general approaches to reduce problems include:

  1. Prevent breeding by making manure unavailable or too dry or wet for the larvae to survive or kill the larvae before they become adults
  2. Kill adults before they cause harm or start to produce eggs
  3. Exclude adults entrance by using screens or other barriers

Facilities housing animals should be designed for easy removal of manure and cleaning of stalls frequently. Waste should be disposed of properly by either burial, spreading in a thin layer (less than 3 cm) on open fields, submersion in water, or aerobic composting.

Manure accumulation in pastures should be minimized by spreading and breaking of manure pats so that they dry faster and become unsuitable for larval development. Also, rotating pastures allows for less manure accumulation in one area.

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