Quickbayt Fly Bait

I am not sure if Bayer has changed its formula to something less toxic or the flies are immune to it. In the past years this stuff use to work great. It attracted the flies they ate a little and in front of your eyes the flies would die on the spot. Within days of using this we could find hundred of dead flies around it. This latest batch does not appear to do anything. We see flies land on it, appear to be eating it but then just fly away. No more dead flies. Either we got a bad batch or the ingredients have changed and are no longer effective.