Ask the Vet

Walk-Through Fly Control

Field studies in central Missouri indicated the walk-through fly trap produced roughly 50% control of horn flies averaged across the season. (Image from University of Missouri archives)

QUESTION: I have a small herd of polled Herefords. I like to think I do a good job of fly control, but I always want to do better. I seem to remember reading an article years ago about a little shed the cows would walk through and remove the flies. I think it was from the University of Missouri. Do you have any knowledge of this?

ANSWER: The concept you describe was developed in the late 1930s by Willis Bruce, a USDA entomologist. Before it was ever commonly adopted, World War II started, and horn fly control took a backseat to winning a war. After the war, DDT and a host of other insecticides were introduced, and the idea fell off everyone's radar until two USDA employees rediscovered Bruce's paper while researching horn fly control.

By 1986, pyrethroid resistance was widespread enough that the University of Missouri Extension service began promoting the use of the fly trap as another tool in horn fly control. Today, it's fair to say fly control is getting more challenging with each passing year.

I like to apply Integrated Pest Management (IPM) concepts that incorporate various approaches and methods to achieve control and minimize development of resistance. The fly trap certainly fits well into an IPM program. The issues with it involve cost of building (or having it built); need for a location where cows walk through on a regular basis; and maintenance of the trap and surrounding area.

A fly trap structure won't provide complete control, but research by the University of Missouri showed it could take fly numbers below the economic threshold of 200 flies per cow. This was based on the university study and may or may not reflect how the trap would work in a real-world application.

Judge for yourself whether it's worth a try and how effective it might be in your environment. For more information on the concept and a blueprint, visit