Livestock Entomology

Horn Fly Project - 2011

The horn fly project is an ongoing project that is conducted on an annual basis to see how different insecticidal ear tags perform from year to year. The following information is from the Summer of 2011.

The horn fly project is an ongoing project that is conducted on an annual basis to see how different insecticidal ear tags perform from year to year. The following information is from the Summer of 2011.

Facts about horn flies


  • Considered the most important external parasite of cattle
  • With high summertime populations, they cause cattle to lose weight and lower milk production
  • Economic infestations range from 200 to 300 or more flies per animal and usually develop in late May or June and then persist into the fall
  • Horn flies reduce beef production efficiency and the economic loss is manifested in growing cattle
  • Normally, growing cattle gain an extra 1.5 pounds per week when horn flies are controlled
  • Horn flies are a greater problem in pastured cattle because they require a fresh, intact manure pad to complete their life cycle
  • Adult horn flies spend their entire lives resting and feeding on cattle, although female flies leave cattle occasionally to lay eggs
  • Life cycle development from egg to adult fly requires about two weeks
  • Because the horn fly spends all of its adult life on cattle, control with insecticides can be highly effective
  • Just as the habits of the horn fly make the pest vulnerable to insecticide treatments, this same behavior can create problems with insecticide resistance
  • Continuous use of the same insecticide or class of insecticides will eventually result in fly populations that cannot be controlled 



Project details

Fly counts are taken weekly from four groups of fifteen cattle each. Three groups were treated with different insecticidal ear tags. The fourth group is the control.

The ear tags used in this project include XP 820, Warrior, and Python Magnum.


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Weekly graphs 

The following are weekly graphs with the average number of flies for each of the four groups. These graphs show how each of the tags performed on a weekly basis compared to the control group.

  • Week 1
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  • Week 2
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  • Week 3
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  • Week 4
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  • Week 5
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  • Week 6
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  • Week 7
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  • Week 8
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  • Week 9
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  • Week 10
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  • Week 11
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  • Week 12
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  • Week 13
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  • Week 14
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  • Week 15
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  • Week 16
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  • Week 17
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  • Week 18
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Actual fly counts

The following pictures are actual live cattle with estimated fly numbers to allow you to compare to your animals at home. 


100+ Flies


300+ Flies




  •  400 + Flies
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  •  500 + Flies
    • flypic 6.jpg

information to know before you buy ear tags

The following is information over horn fly insecticide resistance management and how to properly rotate tags each year.


  • Begin horn fly control procedures in the spring when cattle average approximately 200 horn flies.
  • If ear tags are used, the insecticide classes must be rotated. Do not use a pyrethroid ear tag more than once every three years. Do not use an organophosphate ear tag more than two years in succession. Continuous use of ear tags in the same insecticide class will eventually result in horn fly resistance.
  • Remove ear tags at the end of the fly season or when they lose their effectiveness. Do not tag cattle more than once per fly season, regardless of insecticide class.
  • If additional horn fly control is needed later in the year, use sprays, pour-ons, dusts or backrubbers. If possible, alternate insecticide classes when changing control methods.
  • If pyrethroid ear tags have failed to control horn flies in the previous year, pyrethroid insecticides in any form should not be used for at least two years. In the meantime, use non-pyrethroid ear tags, sprays, pour-ons, etc.
  • Pyrethroid Tags should be used NO more than once every three years
  • Organophosphate Tags should not use more than two years in a row
  • What animals should receive tags? 

       YES: Heifers, Cows and Weaned Calves

       NO : Bulls and Calves still on their mother


Types of Insecticidal ear tags 

The following are a list of insecticidal ear tags available on the market today.

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