No, no poison. The flies enter through a baffle on the top of the bag, get trapped, and drown in the water. The attractant is in dry form when you buy the back, inside a mesh bag. When you add the water the dry solids (rotten egg yolks) dissolve into the water in the bag. That attracts the flies. And it stinks so keep it away from the front or back door of the house. For the house I place mine near the garbage container on the chain link fence--that's at least 50 feet from the front door. The second bag is about 90 feet from the front door on the opposite side of the front yard. For the coops I do the same--quite a few feet away. Don't place it inside the coop--it will draw in more flies than you want.