Unnecessary Pests: Horn Fly

Larry Morehead

Larry Morehead

Horn flies are one of the most economically damaging pests of domestic cattle. They cause billions of dollars of damage and loss to the cattle industry each year. The horn fly is a small blood-feeder found in constant association with grazing cattle and in smaller numbers on drylot or indoor cattle. They are ferocious and painful biters and more than 400 per animal will affect the health and productivity of cattle.

The male and female horn flies will take bloodmeals 20 to 30 times a day. The adult horn flies stay in contact with the cattle, resting on them between feedings. They will be seen on the withers, back and side of the cattle and move to the belly during hot times of the day.

Eggs are laid exclusively under the edges of fresh dung pats minutes after defecation.

Horn flies occur mostly on the cow. Not treating mama cows can lead to a 12% decrease in the average daily growth rate of nursing calves. The growth rate of yearling stocker feeders may be decreased by  about 16%. A 12% loss of gain on a calf could easily be 45lbs per head over the grass season. At today’s market prices, that would be around 90 dollars per head.


Larvacides provide control against developing larvae. IGR (insect growth regulators) were developed specifically for horn flies and other filth flies developing  in the manure. The active ingredient within IGRs targets  just the developing flies and has little to no affect  on other insects or mammals.

IGRs can be fed to cattle by mixing them in with mineral or in mineral tubs. This is one way of controlling the fly predators with products cattle need.

For more information contact your local United Farmers Cooperative.