Boston’s rat infestation is being exacerbated by the Mass and Cass drug and homelessness crisis that has spread like wildfire into surrounding neighborhoods since the long-standing Atkinson Street encampment was removed by the city two years ago, according to a city councilor.

Councilor Ed Flynn joined the Boston Police Department and the Wu administration’s coordinated response team Friday for an eye-opening public safety walkthrough of South Boston’s Andrew Square neighborhood — where residents shared that rats are quite literally being fed by the city’s open-air drug market, due, in part, to homeless people and addicts rooting through and scattering trash.

“One woman talked at length about a homeless person constantly opening her garbage and throwing it on the sidewalk and on the street, and seeing huge rats as well,” Flynn told the Herald.

Homeless and drug-addicted people who used to frequent the long-standing Mass and Cass encampment but have spread out into surrounding neighborhoods since the city ordered the removal of Atkinson Street tents in late 2023, are also worsening the city’s rat infestation with their homemade grills, Flynn said.

The makeshift grills come in handy for homeless people living and sleeping in a particular area, but are like candy to the rats who soon become their cohabitants, as well as becoming the unwelcome neighbors of nearby residents.

“The cooking and discarded food led to considerable rats in the area, along with the trash thrown on the sidewalks,” Flynn said.

One South Boston resident who took part in Friday’s walkthrough but asked not to be named said part of the problem is the way trash removal is handled in parts of the city. Other factors attracting rats include human and dog waste, the resident said.

“The rat issue basically comes down to control of the trash, and that isn’t happening,” the resident said. “The City of Boston still allows for trash to be put out in a plastic bag the night before pickup, and sometimes that is not good, because either the rats get in it, the cats get in it, the raccoons, the people.”

Steve Fox, chair of the South End forum, said the same types of trash-driven rat issues are happening in the South End neighborhood, which has been hit hard by Mass and Cass spillover, but described a more antagonistic situation.

“We don’t have containerized trash,” Fox told the Herald. “We put our trash out on the sidewalk in plastic bags, and what we have been seeing is the willingness on the part of the people walking by to rip them open for no apparent reason.”

People aren’t searching for plastic bottles to cash in, and then closing up trash bags, as is typical for other downtrodden people who rummage through trash, Fox said. The type of behavior he’s seen of late is more malicious, he said.

“What we have seen at Mass and Cass is a willingness on the part of people who are just willing to rip the trash apart for no appar

ent reason, not looking for returnables, but to just seemingly cause destruction,” Fox said.

“In fact,” he said, “we’ve actually been hearing recently, among those who are professionals dealing with homelessness and addiction, that there’s some evidence that there are people who suffer from a mental illness or a mental deficit that suggests that they are willing to cause that kind of destruction as part of an overall mental syndrome.”

The destruction is a way for the afflicted to express their anger or hostility, Fox said of what his community group has heard from psychiatric professionals.

Whatever the reason, he said, the trash strewn by Mass and Cass inhabitants has attracted rats. People can put out their trash as early as 5 p.m. the night before pickup, which may not occur until 2 or 3 p.m., or up to 10 hours later.

Fox said the generosity of food banks, church groups and other charitable organizations also tends to backfire, unless the donations are tightly regulated. Food given to addicts and the homeless in need at and around Mass and Cass is often left discarded on the streets and sidewalks, which further attracts rodents.

While food donations have always been an issue for the neighborhood, Fox said the “craziness associated with ripping bags open and being destructive is new to the Mass and Cass environment,” and “we’re seeing more of it spread out over a wider area.”

“It’s typical of the major problem that we’re seeing,” Fox said. “This is just one manifestation of the larger problem that we’re seeing, which is a result of the city moving people off Atkinson Street. We are seeing dispersion — what we in the South End now call the Mass and Cass diaspora that has moved everybody into the inner neighborhoods of Roxbury and the South End.

“That has caused us no end of problems, and rats are just one dimension to that.”

Flynn, who represents South Boston and part of the South End, has renewed his push for the city to establish a standalone pest control office led by a rat czar, by way of an ordinance he filed with the City Council last week.

He cited a recent study from Tufts University that found rats in Boston are spreading leptospirosis, a bacterial disease that can be deadly to humans.

“Residents are extremely concerned about the escalating rat population in Boston, and it’s impacting every neighborhood across the city,” Flynn said.

Councilor-at-Large Erin Murphy, who took part in last week’s Andrew Square walkthrough, said she supports Flynn’s “renewed call for a rat czar to lead a more aggressive, citywide strategy.” She sees the city’s rat infestation as an unchecked “public health crisis.”

“As a lifelong Boston resident, I’ve never seen the rodent problem this bad,” Murphy said. “Neighbors across every neighborhood are saying the same thing — the rats are out of control.”

Kevin Conroy, who lives in South Boston with his wife, said rats have “pretty much destroyed our quality of life.” The couple’s backyard is so infested that they can’t have anyone over this summer and all their landscaping had to be removed.

“They’re fearless,” Conroy, 68, told the Herald. “I walked right up to them and they were just kind of ignoring me until I hit them with a shovel. … They’re everywhere. It’s just crazy.”

John Ulrich, assistant commissioner of the Boston inspectional services department’s environmental services division, said he treated Conroy’s property with carbon monoxide, along with other parts of that neighborhood, earlier this month.

Ulrich and Luke Hines, who has been designated as the point person for the city’s rodent action plan by the mayor’s office, spoke of efforts underway to better educate residents about proper trash removal and incorporate new technologies, including artificial “rodent sensor” intelligence and sewer traps via a pilot program with the Boston Water and Sewer Commission, to tackle the rat problem.

Hines said the city plans to stick with its multi-departmental approach, rather than create a standalone pest control office, as recommended by a city-commissioned report released last year by renowned urban rodentologist Dr. Bobby Corrigan.

The Wu administration Corrigan’s report is guiding its rat-control work moving forward.

The city’s “multi-faceted approach” is crucial, Hines said, “to really try to mitigate rodents as fast as possible and improve the quality

of life for all residents.”