How Many is Too Many?

An effective control program keeps horn fly levels to fewer than 200 per animal. This at-a-glance-guide will help you easily evaluate the effect that horn flies currently have on your herd. Keep these other assessment tips in mind, too.

  • The horn fly is charcoal gray and approximately five millimeters long (half the size of a typical house fly). 
  • Adult horn flies are located on the backs of cattle, often clustering on the midline and spreading down the sides. Sometimes, they settle around the base of cattle horns. When the weather is hot, they may move onto the animals' undersides. 
  • It's easiest to make the most accurate estimate in the morning, when horn flies are on the upper sides of the cows.
Excellent rate of flies on cattle
Good rate of flies on cattle
Average to Below
Average to Below rate of flies on cattle
Unacceptable rate of flies on cattle