Officials in Medicine Hat say rats may be wising up to a plan to kill them with poison-laced hay bales.

Solid waste manager, Ed Jollymore, says they have to keep changing the location of the bales so the rats will not suspect.

More than 145 rats have been cornered and killed so far, but none by the hay bales.

Jollymore hopes the reason the critters aren’t attracted is that there aren’t many left around.

He tells The Calgary Sun they hope the colder weather may drive more rats to the traps.