Urban Rats Have a Deadly New Enemy 3 major US cities are using dry ice to combat their rodent problems By Michael Harthorne, Newser Staff Posted Sep 16, 2016 6:56 PM CDT 52 comments Comments (Pixabay) (Newser) – Rats have a deadly new enemy, and and isn't cats with tiny knives strapped to their paws. USA Today reports three major US cities are combating their rodent problem with dry ice. It works like this: Pieces of dry ice are dropped into rat burrows in city parks, then the exits to the burrows are covered with dirt and newspaper. As the dry ice melts, turning from frozen carbon dioxide to a gas, it suffocates the rats. “When I first brought up the idea, people around here thought I was cuckoo for Cocoa Puffs,” the assistant commissioner for Boston’s Inspectional Services says. But after the city immediately found dead rats in 80% of burrows where dry ice was used—according to CBS Boston—the method spread to New York City and then Chicago. Experts say the dry ice method is more humane than traditional rat poison, CBS Chicago reports. It also leaves the dead rats to decompose out of sight underground. Besides being cheaper than traditional rat poison—Chicago is getting its dry ice for 50 cents per pound—its use doesn't pose any threat to humans or other animals in city parks. "I am glad they are trying something new that’s not toxic,” a photographer who watched a hawk die after it ate rat poison tells the New York Daily News. And while dry ice won't completely replace poison, it appears to be an effective new tool. Officials in Chicago say there are 60% fewer rat burrows in parks where they're using dry ice.