I made this very cheap, easy trap about 5 years ago and am so impressed with how many baddies it caught in the first two days I put it out this year. It’s modeled on a horsefly trap, though it’s always been better at greenheads than horseflies (which I haven’t seen out in force yet this year although there is one in the trap). All it requires is scrap wood, a beach ball, some sort of mesh like for screen doors, clear plastic containers (I get them from the salad bar), something to hang the beach ball and secure the containers (I use bungee cords and twine), and black spray paint. Super easy and so satisfying to see all the dead pests in it! I haven’t had much issue with it catching beneficial insects either. I highly recommend this easy little project!
ETA a link since some people can’t see the photos: http://thesmallhorsefarm.blogspot.com/2016/07/biting-fly-trap.html?m=1