RESCUE! Disposable Fly Trap contains a fast-acting fly attractant that starts working as soon as you add water. Lured by the scent, flies enter through the yellow top cap and drown in the water. This trap is specially designed to handle areas with heavy fly concentrations. The RESCUE! Disposable Fly Trap is completely disposable which eliminates touching the bait or the flies. This trap holds up to 20,000 flies!