Environmental health and rodent control programs may see an increase in service requests related to “unusual or aggressive” rodent behavior, the agency said on its website on Thursday.
“The rats are not becoming aggressive toward people, but toward each other,” Bobby Corrigan, an urban rodentologist who has both a master’s degree and Ph.D. in rodent pest management, said on Sunday. “They’re simply turning on each other.”
Dr. Corrigan said pest control professionals in the city have sent him photos of rodent cannibalization and slaughter.
“They are going to war with each other, eating each other’s young in some populations and battling each other for the food they can find,” Dr. Corrigan said. “But the rats that live and eat in residential blocks probably haven’t noticed a single bit of difference during the shutdown.”
To keep hungry rodents at bay, the C.D.C. recommended sealing access to homes and businesses, removing debris, keeping garbage in tightly covered bins and removing pet and bird food from yards.
Dr. Corrigan said the C.D.C.’s latest guidance should put homeowners on alert. Whether in rural America or in urban areas, people who don’t ordinarily see rats might start noticing them.
“You’d be smart to ask yourself: How do I do my trash and does how I do it completely deny a wild animal?” he said. “And look at the base of your door. Get out a ruler to see if there’s a space below the door — half an inch will let them in.”
Michael H. Parsons, a visiting research scholar at Fordham University studying how rats are migrating en masse from areas near closed restaurants, delis and arenas to new environments, said rats usually don’t travel far for food and water. This minimizes the risk of them being seen by people and predators, he said.
But in recent weeks, pest control professionals have seen more rats venturing out during daytime hours and entering homes that had not previously seen rodent activity, Jim Fredericks, the chief entomologist for the National Pest Management Association, said on Sunday.
Suburban neighborhoods, often adjacent to shopping centers and other businesses, are also seeing new infestations, he said.
Dr. Fredericks said there is no evidence that rats can be infected with Covid-19 or that they can spread it to humans. Still, they are a public health risk. Rats can transmit other diseases and a professional should be called if an infestation occurs, he said.
Once the restaurants reopen, the rats will return to their reliable food sources. Dr. Fredericks said he does not expect the overall rat population to be significantly affected by the shutdowns.
“They’re resilient,” he said. “Rats are good at being pests.”