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, and many others. Powder attractant is contained within the trap itself. Attractant dissolves and activates quickly when water is added to the bag. Trap's design eliminates touching the bait or the flies. Completely disposable. Catches up to 20,000 flies.