I ordered two of these and placed one in the narrow laundry room just inside the back door where all the flies come into the house (I leave the back door open for my two dogs to go in and out of the house when I'm home.) and put another one in the kitchen where the flies hang out while I'm cooking. Apparently Colorado flies are far too smart to get close to these things. I have not caught ONE. The only way these 'traps' are going to eliminate flies in my house is if the flies die laughing.