The RESCUE Disposable Fly Trap catches common nuisance or filth flies — hundreds of the most prevalent species including house flies, false stable flies, blow flies, blue and green bottle flies, flesh flies, face flies and many others. How it works: Inside the RESCUE Disposable Fly Trap is a bait that flies find irresistible. This attractant is comprised of food and feed ingredients, and other food flavorings generally recognized as safe. The attractant dissolves and activates when water is added to the bag. Lured by the scent, flies enter the trap through the yellow top cap and drown in the water.