Wet Spring Means Ideal Fly Conditions

Sponsored by: CRYSTALYX® Brand Supplements

Weather forecasters are calling for El Nino weather patterns to continue through the spring, meaning wet and relatively mild conditions. Unfortunately, these are perfect conditions for the horn fly to propagate. Excessive horn fly populations can literally suck the profit out of your cattle operation! Biting flies reduce weaning weights, lower milk production and spread disease.

The horn fly alone is estimated to cause losses of between $700 million and $1 billion to the U.S. beef industry annually. Losses tend to be greatest in lactating cows and growing calves. The irritation and blood loss caused by biting horn flies can reduce calf weaning weights by 12 to 14 pounds and average daily gain in yearling steers can be reduced as much as 30 pounds during the grazing season. Horn flies also cause lowered sexual libido in bulls, resulting in reduced reproductive efficiency. Horn flies are also vectors for the transfer of diseases such as anaplasmosis, anthrax and mastitis caused by Staph. aureus.


Growing calves are particularly susceptible to the negative effects of horn flies. Reduced weight gains of up to 30 lbs have been reported.


Adult horn flies are dark gray and about half the size of the housefly. The life cycle is completed in 8 to 45 days depending on temperature and humidity. Horn flies tend to rest quietly on the back and shoulders of cattle until disturbed. Horn flies rarely leave their host except to lay eggs, to move to other cattle in the herd, or when cattle enter buildings. Most feeding occurs along the underline of the animal and results in scabby, often bleeding, sores. Each fly is estimated to feed 20 times each day! Grazing time is disrupted, resulting in significantly reduced weight gains and daily production.

Horn flies survive the winter by remaining dormant as pupae in the soil. Adults emerge when temperature and moisture conditions are right. Horn flies emerge when average daily temperatures reach about 65° F for a period of at least two weeks. In the Southeast, flies may remain active year-round. In general, fly populations tend to peak in early summer and decrease as conditions become hot and dry. Methods of horn flies control are many and varied but most rely upon chemical control. 


Adult horn flies spend their time almost exclusively on the animal, while the egg, larval and pupa stages are all in the manure pat.


Pesticide-infused ear tags have been widely utilized with success in recent years. However, this method requires the labor and stress of handling cattle twice - once to apply the ear tags, and another to remove these tags. Failure to remove ear tags as recommended has widely contributed toward development of pesticide resistance and has reduced the overall success of this method over time.

Sprays and pour-on pesticides can also be effective; however they also require extra labor and handling of cattle. Another point is that they offer short-term control (one month or less). Therefore, in order for this method to offer optimum control, cattle must be handled and treated monthly throughout the fly season. Additionally, there is the fact that the applicator must handle these chemicals and the associated safety issues therein.

Some utilize backrubs laced with pesticides and oil. This method yields mixed results. It is difficult to get all cattle within the herd to properly utilize these rubs on a consistent basis. Additionally, labor is required to properly maintain these rubs to make sure they are not dislodged and contain effective levels of pesticides.

However, one of the most convenient and effective methods of horn fly control involves self-fed mineral supplements and blocks. These supplements contain active ingredients that interrupt the horn fly life cycle, effectively reducing the overall population of horn flies. This method requires no additional labor and no cattle handling unlike the previously mentioned methods. Just provide free-choice supplementation to cattle as you normally would.

Self-fed supplements containing either Rabon® Oral Larvicide, Altosid® IGR or Clarifly® conveniently and effectively control horn flies. All three active ingredients act to disrupt the horn fly lifecycle to prevent future generations of flies. Neither Rabon®, Altosid® nor Clarifly® have slaughter withdrawal times and all can be fed to all classes of cattle including lactating cows and calves.

For best results, start feeding self-fed fly control products for at least 30 days before the projected last frost and 30 days after the first frost in the Fall. In some areas, these dates will overlap. Locate barrels or tubs where cattle congregate (near watering, loafing or shade areas, etc.). Follow label directions on stocking rates and target intake. Increase or decrease the number of containers or change locations if necessary to adjust for proper consumption. Remember that neither Altosid®, Clarifly® nor Rabon® will kill adult flies. Use of approved adulticides will be necessary to eliminate adult fly populations if these supplements are introduced after adult horn fly infestation is already established.

In summary, horn flies represent a costly drain on profitability. Fly control will be critical this spring due to ideal conditions for fly reproduction. Visit www.crystalyx.com to learn more about available options and how these supplement products can help improve profitability in your herd.

Rabon® is a registered trademark of Bayer HealthCare, LLC

Altosid® is a registered trademark of Welmark International

Clarifly is a registered trademark of Central Garden & Pet Company