Your Ag Newsroom


Scout Pastures for Flies Impacting Cattle Now

July 11, 2016

Face and horn fly populations are increasing in pastures, so now is the time to scout for the pests.

“Scouting for flies is essential to determine when and if action needs to be taken to control fly populations,” says Patrick Beauzay, coordinator of the North Dakota State University Extension Service’s Integrated Pest Management program. “When pest populations reach an economic threshold, proper control is imperative to circumvent a portion of the $1 billion lost annually in the U.S. due to horn flies alone.”

Using the right control at the right time for the right duration will control pests effectively with the least unintended consequences, according to Gerald Stokka, NDSU Extension veterinarian and livestock stewardship specialist.

Scouting procedures include:

  • Identifying specific types of fly species on cattle
  • Determining relative number of flies
  • Determining which types of control are appropriate

Here are some tips on identifying horn and face flies and how to scout for them:

  • Horn flies are grayish and look like small houseflies. These blood-sucking flies feed up to 20 to 30 times per day. This constant biting causes pain and stress, and can reduce weight gains in cattle by as much as 20 pounds.

When scouting for horn flies, focus where they spend most of their time on cattle: clustered on the cattle’s head, shoulders and back. On hot days or during rain, horn flies often move to the animal’s belly.

To monitor horn fly populations, count the number of flies on the head, back and shoulders of at least 15 cattle. To simplify that process, count the number of flies on a single side of the animal and multiply that number by two.

“If the average count exceeds 100 flies per animal, producers should implement control measures,” NDSU Extension beef cattle specialist Carl Dahlen advises. “When counts reach 200 flies per animal, the economic threshold has been reached and animals will have significant weight loss if no control actions are taken.”

  • Face flies look like large, dark-colored house flies. Face flies are nonbiting flies that feed on animal secretions, nectar and manure liquids. Female face flies cluster around the eyes, mouth and muzzle of animals, whereas males spend little time on animals, feeding primarily on nectar and manure.

When scouting for face flies, look at key areas on the animal, but also remember that face flies rest on forages, fences and other structures near cattle. Face flies transmit several eye diseases, including pinkeye and bovine rhinotracheitis (IBR).


Common methods of fly control used in pastures include:

  • Ear tags containing insecticides that are released slowly into the animal’s hair by the animal’s movement
  • Pour-on or sprays
  • Self-application devices (dust bags or oilers)
  • Feed additives
  • Nonchemical walk-through trap

Ear tags can provide effective control of horn and face flies if producers select the appropriate insecticide. Be sure to read label instructions on the number of ear tags (one or two) to apply and rotate the insecticide class to prevent resistance.

Pour-on and sprays can provide short-term relief from flies, but the chemicals need to be reapplied throughout the fly season.

Dust bags are sacks filled with an insecticide dust. When an animal bumps or rubs against the bag, a small amount of dust is deposited on the animal. When cattle rub against the oiler device, the insecticide is rubbed into their skin.

Dusters and oilers provide limited control if cattle can use them when they choose. However, forced use has been shown to reduce horn fly populations by as much as 90 percent.

One way to force cattle to get fly control is to make them to walk through an insecticide or nonchemical measure to reach water or minerals or access other portions of the pasture, says Miranda Meehan, NDSU Extension livestock environmental stewardship specialist.

Nonchemical traps work by brushing flies off the backs of cattle, then attracting the flies to a light at the top of the trap and into an inverted-cone trap. Once captured, they are unable to escape. Research indicates that this type of trap provides a 50 percent reduction in the number of horn flies in a herd.

Feed additives are insecticides that pass through the animal’s digestive system and destroy the developing fly maggots in the manure. They are effective in killing 80 to 90 percent of the developing fly larvae. One disadvantage of feed additives is fly migration from untreated herds, which can decrease the additives’ effectiveness.

Here are some factors to consider when selecting a method to manage horn and face flies:

  • Life cycle of the species you are managing
  • Treatment threshold
  • Horn and face flies are capable of flying miles in search of a host
  • Horn flies can develop resistance to treatment

Source: North Dakota State University