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Horn Fly
Courtesy of R. Grantham, OSU Department of Entomology and Plant Pathology

A light brown/green colored fly on a white background.

Horn Flies are smaller flies, they will be found on the back and sides of the animal. During the heat of day they will migrate to the belly. Both male and females feed on blood. Populations develop in late May or June and persist into the fall.


Life cycle: Horn flies are holometabolus, meaning they have a complete life cycle (egg, larvae, pupae, adult). The females need to take a blood meal to reproduce. Horn Flies are a greater problem in pastured cattle because the females need an intact fresh manure pad to complete the life cycle. The life cycle can be completed as quickly as two weeks.


A large amount of horn flies on the sides and belly of a black cow.


Damage Caused: Horn Flies are considered the most important external parasite of cattle. When summer populations reach their peak they can cause weight loss, lower milk production, and reduce beef production efficiency which is manifested in growing cattle. Growing cattle can gain an extra 1.5 pounds per week when horn flies are controlled.


How to control: Economic infestations range from 200 to 300 flies and up. Withholding treatment until populations reach 200+ flies is recommended. Horn flies spend their life on the cattle, allowing insecticides to be highly effective. This behavior can also cause issues with resistance. Resistance to insecticides can develop quickly because horn flies have multiple generations with in the summer months. When using insecticides, a rotation must be used to avoid resistance from year to year. If using ear tags certain measure must be taken to ensure effectiveness.


For more information on Insecticide Ear Tags, Click here.


Information on insecticidal sprays and pour-ons coming soon!


Horn Fly Projects 

Horn fly projects are conducted on an annual basis to see how different insecticidal ear tags perform from year to year. The following information is from the summers 2010 - 2015. Click on the links below for more information on the yearly projects:

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