That's because the gnats, aphids, brain borers, nasal nymphs or whatever they're called are out in force. And they tend to get in your hair, literally.
So, no hair means debugging your person is a whole lot easier when you are about to go back indoors. Sure, they'll still be clinging to your clothes. But you can flick most of those off. Extricating them from your tresses is another matter entirely.
Bug season also raises questions about the advantages of certain hair colors.
If you have dark hair, the bugs aren't so visible that someone 10 feet away can note that you are infested. On the other hand, light colored hair does allow people to inspect themselves with some assurance that most of the uninvited hitchhikers will be detected.
Of course, some of the insects look white. So, in that case, the opposite scenarios would come into play.
In any event, here in a city of ballcap wearers, you might want to think about putting something on your head before you go out.
Just so long as it's not a Texas Rangers cap.