On occasion we have observed severe problems with very aggressive or determined rats. They may have marked their territory, are hormonally driven, and have a strong drive to preserve their adopted home. In these cases a broader approach is necessary to persuade them to nest elsewhere.
Unfortunately, getting rid of pack rat problems is not
a one step process, but it is often a continuing process
of control and elimination.
CHICAGO-Some of America's biggest metros have unleashed a chilling-and seemingly effective-new killer in the unending urban war against rats: Dry ice.
Sanitation officials in the nation's third largest city told USA TODAY they recently launched a pilot program at four Chicago parks to test the effectiveness of dropping chunks of dry ice-frozen carbon dioxide-into burrows to try suffocate rats as the dry ice sublimates from a solid to a gas.
Chicago began the experiment with dry ice in late August, following Boston, which became the dry ice pioneer when it launched its pilot in March, and New York City, which launched its test program in May.
"When I first brought up the idea, people around here thought I was cuckoo for Cocoa Puffs," said Leo Boucher, assistant commissioner for Boston's Inspectional Services, which consulted with Chicago as it launched its dry ice pilot. "But we all became believers. It works."
The odorless gas in solid form-commonly used by stagehands to create an artificial fog effect and by merchants trying to keep perishables from spoiling-also can be deadly to small animals at high concentrations.
Earlier this week, USA TODAY observed Chicago sanitation department workers at one of the city's oldest parks scoop chunks of smoking dry ice into a burrow before quickly covering the entry and exit holes with dirt and newspaper to stop any rats from escaping as the -109.3-degree Fahrenheit gas dissipated. Sanitation workers say they treat burrows during morning hours, when rats are less active and most likely to be huddled inside the burrows.
The asphyxiated dead rats then decompose in place and out-of-sight of city denizens who count the disease-carrying vermin among the vilest of indignities of urban living.
While the program is only a few weeks old in Chicago, officials there say it shows promise.
"We are seeing 60% fewer burrows in areas where we are using the dry ice," said Charles Williams, Chicago's streets and sanitation commissioner. "It's more environmentally friendly, and it's very humane on the rodents as well."
The dry ice experiment comes as many big U.S. cities are experiencing an explosion in rat complaints from residents, according to a USA TODAY analysis published earlier this year. Among the cities with the biggest spikes in complaints are Boston, Chicago, New York and Washington, D.C.