The big bag fly trap contains a fast-acting fly attractant that starts working as soon as you add water. Food and feed additives are combined with other dried ingredients to make the attractant. 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 big bag fly trap is completely disposable which eliminates touching the bait or the flies. This huge trap holds up to 40,000 flies!