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Stable flies cause economic losses

by Wyoming Livestock Roundup

Studying the behavior of cattle can alert producers to potential problems. If the cattle are bunched in the corner of a pasture, it can signal an excessive fly population. 

“There is nothing worse than seeing an animal tormented by flies,” says Dave Boxler, who is an entomologist with the University of Nebraska at North Platte. “They are throwing their head, stomping and not grazing when they should.”


Stable fly populations on yearling steers can impact average daily gains by as much as 0.44 pounds per day, according to some studies at the University of Nebraska in North Platte. 

“It can add up, and that’s with stable fly numbers less than five per leg,” Boxler says. 

Bunching of cattle in pasture corners can be counter-productive. In sandy areas, it can cause blowouts to develop, and if the problem persists, bunched cattle can even push fence lines to the ground. 

Stable flies are biting and sucking insects typically found on the legs of cattle. They take a blood meal from the animal, then find a resting spot to digest the meal. If the cattle remain untreated and the population is high enough, they can cause the cattle to become anemic. 

“We had some pretty high populations of stable flies last summer,” Boxler says. “We took fly counts twice a day for a study into some new insecticides, and we’ve found stable fly numbers in excess of 15 to 20 flies per leg on untreated animals. That’s pretty significant.” 

Fly populations

The amount of moisture received in May, combined with the warm temperatures, creates a perfect environment for breeding stable flies. 

“Through the mid to latter part of the summer, if we see hot temperatures and no moisture, stable fly numbers should start to decline naturally. In the areas where they develop, the decaying organic material will not have enough moisture to allow their life cycle to be completed. They are dependent on moisture for their development.”

Fly control

In the meantime, Boxler encourages producers to provide some sort of fly control for their animals, whether they are infected with the stable fly, horn fly or face fly. 

“The population of flies we have will impact animal weight gains and welfare. By providing some fly control, we will reduce some of the economic impact on our cattle,” he notes.

Producers may have to rely on sprays to control the population. 

Fly tags and other methods that are available for horn fly control won’t work on stable flies, Boxler says. 

“Sprays can be applied directly to the animals using a low pressure sprayer with a utility vehicle or a mist blower,” he says.

If producers can identify resting sites where stable flies go after taking a blood meal, those resting sites can be treated to rapidly reduce the population. 

“Resting sites vary from the shaded side of a water tank or windmill to a windbreak,” he says. “We can identify those sites best during the heat of the day. The flies can actually be heard buzzing, or we may see their calling card, which is little black specks of feces. That will indicate a resting site for stable flies.”

  “If we spray that area with the same product we use to spray the animals, it will be effective in reducing the stable fly population,” he says.

Spray op[tions

Boxler recommends sprays like permethrin, which is a synthetic pyrethroid, or insecticides like Co-Ral, Prolate or Lintox. Although Co-Ral and Prolate/Lintox are very effective for stable fly control, they are only labeled for use on livestock over three months of age. 

There are also a number of natural products on the market like PyGanic, which is a natural occurring pyrethrin derived from Chrysanthemum plants. Evergreen Pyrethrum is another organic insecticide that is effective. 

Boxler reminds producers these organic products are labeled for direct animal application and have short residual periods.

“They are natural control products, which are very effective, but as stated previously, they are not long-lasting ones,” he notes.

“With a limited number of products that can be used for direct animal application, producers need to remember to rotate to different modes of action,” he reminds ranchers. “All chemicals and insecticides are grouped with a number based on how they work. Rotation through the different numbers during fly season will help producers manage fly resistance.”

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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