Same boat here.
Pretty sad to recently discover that the new parcel of land we bought this winter is a haven for deer flies once the weather gets into summer mode. I had to stop working on my land clearing projects and taking hikes out on the land because a swarm of dozens of deer flies would try to land on and bite my head, neck, arms, etc. It was brutal.
Then I hit the interwebz and found the bright blue + tanglefoot idea. It is amazing how well it works! It's definitely a little annoying to wear a ball cap with a blue solo cup tied to the top, but it keeps me at near-zero biting levels and catches 40+ flies every time I head out there. It makes it possible to enjoy the outdoors and get some work done, and that is just terrific.
I saw that many people say the flies are only attracted to motion, but it's not so simple. The heat plus CO2 emissions from a large mammal is clearly driving their attraction to me. A blue solo cup dangling and swaying in the breeze catches no flies at all, which sucks. For example, when I drive around on a tractor, you can see the flies come check out the heat of the machine, and any moving parts, but they aren't stupid and don't linger long. Within seconds they detect my presence and come after me.
