Pam and Nix have the same active ingredient, Permethrin. So not sure how Pam didnt work but Nix did. Not sure if Nix is residual though. Thats the reason i like Pam is the stuff will stay active for 2+ months once applied and dried. I wipe down the outside of my cage stacks every 6 months as a preventative in case i bring home an unwanted guest. Just spray it on a rag in the garage and then wipe down the outside of the cages. No smell or mess.