Our CT home overlooks a CT River tributary. Between our house and the open water is marshland...perfect breeding ground for deer flies as we learned when we built in the 90s. The plus side is that they're only around, in CT, from about the last week in June till August 1. On the negative side, they are the most evil, unrelenting, GD, SOB insects I've ever come across. Fortunately, we largely avoid them now as we spend our summer days on the lake.
A few things to know. Distinguish these medium sized flies from others by the patterned dark markings on their wings. They are especially attracted to bright blue colors, moving targets and they are always aiming for your head. So, to start, stay away from dancing in your yard while wearing bright blue clothing/hats (which I used to do often but no longer do). They are extremely fast and in peak season will literally swarm your head. They are generally way too fast to swat and will be more active away from your house and in more shaded areas. Repellent of any sort is not effective, and I can't think of anything worse than wearing a net over my head in 90-degree heat.
The solution we discovered was to purchase these deer fly patches which simply adhere to the back of a baseball cap. They entirely change the outdoor experience at this time of year and make it completely tolerable to be outside. They are cheap, extremely effective and last a long time. Instructions say to adhere a single patch to the back of your hat. I usually do that and add one on the top of my hat. It isn't unusual during peak season to come in after working outside for a few hours with 20 or 30 flies on these little patches...and zero bites. The satisfaction is immeasurable. Yes, occasionally one will get through the defense, but the new outdoor experience is night and day.
You may feel a little silly at first with a cap of stuck and buzzing deer flies on your head but at my age, I'm not trying to be sexy. Any chuckles from your family or friends will quickly dissipate once the deer flies make a meal out of them versus you. Then, you'll be laughing at them.
https://www.amazon.com/12-Deerfly-Pa...21477118&psc=1