Seems like this time of the year I always get gnats. I don't know where they come from. So I made a gnat trap to catch them. Make a funnel out of a piece of paper and cut a small amount on the bottom for the gnat to get through.
Then pour some vinegar in a glass and put the funnel on the glass. Use scotch tape to hold the funnel down to the glass tightly. The gnats will smell the vinegar and will follow the scent through the small hole. Once inside, they can't figure out how to get out and eventually drown in the vinegar.
It works like a minnow trap.