The flies in the barn are unbearable
Flies are a manure-management problem wearing a disguise. Every control you buy is working against a breeding site you could have removed instead.
What actually works
Flies breed in **wet** manure and spoiled bedding. Clean on a schedule, keep bedding dry, fix the leaking waterer, and spread manure thin so it dries. This does more than everything else combined.
Real, used commercially, and they work — but only as **prevention**, released early and repeatedly through the season, and they're undone by a sanitation problem or by broad-spectrum fly spray.
Unglamorous, cheap, and genuinely reduces numbers. Site baited traps **away** from where people are — they attract as well as catch.
Same shelf, same failure as every other ultrasonic pest device.
Also searched as
barn flies · fly control livestock · stable flies · manure flies · fly predators · fly spray barn · too many flies