Let us help you get control of your deer and horse flies.

One of the easiest ways to control horse and deer flies is with the H-Trap! All you have to do is place the H-Trap in a sunny area between the source of Tabanid Flies, typically ponds and streams and your animals (and beyond your animals’ reach). Horse and Deer Flies are attracted to the dark ball, thinking it is an animal and blood meal. When the flies hit the ball, they fly up and get trapped in the collection cup at the top. Voilà!
There are also traps that you can build yourself. You can search online for plans to build the home made version by searching for Manitoba Trap.  Another trap that works pretty well is to get something like a kickball and paint it blue (deer flies are particularly attracted to blue), then cover the ball in a product called Tanglefoot (you can usually find this at places like HomeDepot), then hang the sticky blue ball in a tree near where you spend time but beyond your animals reach.

Interesting tidbits: Natural predators of the deer fly include the nest-building wasps and hornets, dragonflies, and some birds like killdeers.