Will cannibalism produce mutant super-rats after COVID-19? Here’s what experts say

Rats are taking to empty streets in search of food as they usually do, but something is stopping them in their tracks: there isn’t any food to munch on.

Stay-at-home orders and business closures related to the coronavirus pandemic are forcing rats to eat each other — a common act among rodents when food is short — but some experts say this could lead to a smarter, more aggressive rat breed.

“The survivors of the rat migration may convey more risk-taking, aggression, and lead to allele frequency changes and adaptation,” Michael Parsons, a biological-sciences research scholar at Fordham University, told Insider. “We could have more resilient rats available for a possible second wave of the pandemic.”

“Will they be more ready than we are?” Parsons added.

The first rats to go are the weaker ones, Parsons said. “Instead of having low-ranking rats looking for entries into our residencies, we have the smartest, most resilient.”

But other experts in the field disagree.

This intense competition among rats “would have to occur over generations” in order for a population of stronger rats to prevail after the pandemic subsides, Matthew Frye, a community integrated pest management educator with the Cornell College of Agriculture and Life Sciences in New York, told McClatchy News in an email.

Another expert admits competition will go up as shutdowns continue, but what’s happening within their communities now is not particularly novel for rats.

“Yes, food shortages may act as a selection pressure, but no, this wont drastically change the species trajectory and overall behavior or phenotype,” Matthew Combs, a postdoctoral research scientist at Columbia University, told McClatchy News in an email. “Rats have become globally successful and persistent pests because they are constantly searching the environment for food, dealing with high mortality and high risk situations.”

Dr. Combs worked with a team on a study published in February that described how gene changes in New York City’s rats have helped them live in urban areas.

He added that a rat’s entire evolutionary strategy is already built for a situation like this, making drastic changes in breeds unlikely.

Rat-eating rats are nothing new, experts say. The rodents typically turn to cannibalism when food is short, when competition for resources are high and when infants are born immature, a phenomenon called infanticide.

What’s happening now — one month into nationwide shutdowns — is a “thinning of the herd” through competition, Dr. Frye said.

The concept refers to the struggle for existence when resources are limited, Dr. Frye said, and is “derived from Darwinian natural selection.”

In stressful circumstances, rats will limit their breeding, Parsons told Insider. Rodents usually breed quickly, with just 23-day pregnancies.

But what the pandemic can lead to are some opportunities to catch up with pest control, Dr. Frye said, “since stressed rats are more likely to interact with rodent management devices.”

In New Orleans, rats were mistaken for “playing in the streets” when really they were eating each other, according to Pest Control Technology.

A pest control specialist there told the magazine he was surprised at how quickly the rats turned to cannibalism just one week after bars and restaurants were closed due to the pandemic.

So Timmy Madere decided to lay out poisonous bait in an effort to control the city’s rat population, the magazine reported.

“They were just destroying bait,” Madere said. “Now, the dropoff has been dramatic. Talking to citizens now, they are just seeing dead ones.”

This story was originally published April 21, 2020 at 11:43 AM with the headline "Will cannibalism produce mutant super-rats after COVID-19? Here’s what experts say."