If any of you frequent areas with deer flies during their in-season (mid-summer), purchase these:
https://www.amazon.com/12-Deerfly-Pa.../dp/B0038RO1YI
I use these at our CT home where, in July, the deer flies are merciless no matter what I'm doing outside. They are also great to have along when hiking at that time of year. These make being outside enjoyable again. Almost every single fly will attempt to land on your head where they get stuck to the flypaper. Yes, you'll feel a little odd with patches of dead or dying deer flies on your cap but given the alternative, who cares.
Note...these are specifically for deer flies (see Thinks photo below) as they nearly always go for the head. They will not work with other biting flies.