American rats have turned cannibalistic during the COVID-19 pandemic as their normal food supplies have dried up.
The US Centers for Disease Control and Prevention (CDC) are warning of "aggressive" rats on their website as new reports emerge of odd behaviour in New York and New Orleans.
"Community-wide closures have led to a decrease in food available to rodents, especially in dense commercial areas. Some jurisdictions have reported an increase in rodent activity as rodents search for new sources of food," the CDC website says.
"Environmental health and rodent control programs may see an increase in service requests related to rodents and reports of unusual or aggressive rodent behavior."
The CDC noted that rodent population upheavals are common during natural disasters, and after they are over, the pest populations often surge.
Bobby Corrigan, an urban rodentologist, told NBC News as restaurants are closed and there are less people out and leaving rubbish, the rats are becoming desperate.
"A restaurant all of a sudden closes now, which has happened by the thousands in not just New York City but coast to coast and around the world, and those rats that were living by that restaurant, some place nearby, and perhaps for decades having generations of rats that depended on that restaurant food, well, life is no longer working for them, and they only have a couple of choices."
He says some rats have resorted to eating each other or their babies to survive.
"They're mammals just like you and I, and so when you're really, really hungry, you're not going to act the same - you're going to act very bad, usually," he said.
"So these rats are fighting with one another, now the adults are killing the young in the nest and cannibalising the pups."
The Guardian reported there have been increased reports of canibilism and infanticide during the pandemic, with lockdowns still in place in many cities.
In New Orleans rats have also been flocking to the streets to find food, particularly in tourist hotspots such as the French Quarter, NBC reported.
"What we have seen is these practices are driving our rodents crazy," Mayor LaToya Cantrell said at a news conference in April.
"And what rodents do, they will find food, and they will find water. That puts our street homeless in dire, dire straits. And that's why I'm so laser-focused on it right now."
Corrigan says the rats could now be looking to get inside of homes to secure food, since they can't find it outside.
"Rats are designed to smell molecules of anything that's food-related," he said.
"They follow those food molecules like heat-seeking missiles — and eventually you know they end up where those molecules are originating."
The United States currently has 1.68 million confirmed cases of COVID-19.