Q: I have gnat-type flying insect swarming in my backyard. What type of insect would be flying this late in the year?
A: My bet, based on experience from previous years, is that the things are the winged form of either green peach aphid or crapemyrtle aphid. For most of the year succeeding generations of these insects are wingless. In fall, winged individuals appear, the better to find mates. I know it is creepy to find them crawling on your neck as you walk outdoors but further chilly weather will soon take care of them.