Horn Flies

Scientific Name

Haematobia irritans


Adult horn flies have dark, shiny bodies with somewhat overlapping wings covering the abdomen. The body is about 3/16 of an inch long, or about half the size of the common house fly. The head features small, brownish-red, downward-pointing antennae, and the thorax is striped on top. There is no appearance of a pattern on the top, back side of the abdomen.

Behavior, Diet & Habit

Horn flies are one of the most serious cattle pests throughout the United States. Since both male and female horn flies are blood feeders, they cause pain, annoyance and interfere with feeding, resting and other normal livestock activities. Horn flies are persistent feeders that reach high population levels in the summertime, thus causing weight loss and reduced milk production.

Horn flies collect on cattle, often gathering on the back and sides of the animal. As the name implies, the flies sometimes congregate around the base of the horns. During hot and sunny weather, they may move downward onto the animal’s belly.

Eggs are laid exclusively in fresh cattle manure. Larvae hatch from eggs in about one day and feed on the manure, passing through three larval stages in about 3 to 5 days. Pupae develop from larvae and it takes only about 3 to 5 days for pupae to develop into mature adults. Newly emerged adults mate on the host and begin feeding. If no host is found, newly emerged horn fly adults can travel several miles searching for a host. During her lifetime, a healthy, well-fed female adult can lay about 400-500 eggs.

The life cycle from egg to adult takes about 10 to 20 days, depending on environmental conditions. Horn flies overwinter as pupae in or under cattle manure piles. Horn fly populations peak in the early summer months, but decline as the temperatures increase during the hot and dry months. However, as the fall months approach and temperatures decrease and humidity and rainfall increase, populations will peak again.

Horn flies got their common name because of their habit of clustering around the horns of cattle, although as mentioned above, the adults generally prefer to settle on the backs of cattle during the cooler part of the day and on the belly during the hotter part of the day.


The short life cycle, multiple generations per year and the large number of flies that a fertile female horn fly lays all contribute to their ability to produce large numbers of flies.

Signs Of A Horn Fly Infestation

Seeing adult horn flies feeding on livestock is the most obvious sign of an infestation.

More Information

Local state and university extension services can provide horn fly management recommendations. If additional information is needed, it may also be helpful to contact your local pest management professional.

There are many ways, often used in various combinations, to help control horn flies in a cattle herd. Briefly, horn flies are killed by exposing them to insecticides contained in an animal’s ear tags, pour-on preparations, sprays, dust bags or back rubs. Another tool is to set a controlled fire in pastures. This technique is effective at helping to reduce the number of horn flies since fires set during the fly’s dormant season (late winter and early spring) alter the cow manure pats and helps reduce the number of pupae that are overwintering in or below them.

Still another useful technique is the walk-through horn fly trap. These traps prey on the horn fly’s hesitancy to enter a dark building. As cattle are moved into the large horn fly trap, flies leave the animal and are then trapped or killed by sticky traps or electrocution.

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.
  • Disease transmission. Horn flies are vectors of several disease-causing pathogens including filarial nematodes that cause stephanofilariasis, a dermatitis characterized by areas of crusted skin on the underside of cattle and bacterial infection in open wounds caused by horn fly bites.