The story of spring flys at Amber Fox reminds me of how we used to handle flys when I was working as a forest ranger, fighting fires and planting trees.
Seems those pesky flys were more on our minds than the bears and even the raging fire sometimes, out there hot and sweaty, persperation dripping off you inside those coveralls, off your face, sometimes people thought you had turned the piss can on yourself. (Piss can in case you have other ideas is not quite what you thought. It was a five gallon metal can that was filled with water and strapped to your back. It had a hose and a piston attachment for squirting much like many kids water guns today.)
If you were staying on the fire overnight, which happened sometimes as darkness set in and the helicopter that you rapelled out of can't fly at night, the flys were enemy number one. It was hot, you were wet, dirty and no way to clean up. You are now on the top of the dating list for flys, not bad if you are into that, but me, no...
We would use a few pop bottles (or beer bottles if you managed to get them by the pre-flight check) inverted with the bottom supported with sticks. The sweet scent would lure the flys. Once in the bottle, they couldn't get out, they can't manouver down in such a confined space. Set up five or six just abit away from where you are cooking at your fire and the flys thin out.
It works much better inside. I have used the following fly trap with great success...
Boy Ricky's fly trap
You need - a two litre plastic bottle, string, a stick or tape, and some smelly bait
Second step, throw away the lid, make four cuts in the lid so it has narrow openings or looks like it has legs.
Voilà Instant fly trap!