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Using Dry Ice To Keep Down Boston's Rat Population

Promising Tool In Keeping Down Boston's Rat Population Gets The Cold Shoulder

Rattus Norvegicus - The Common Urban Rat
Rattus Norvegicus - The Common Urban Rat
Emily Judem /WGBH News
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Using Dry Ice To Keep Down Boston's Rat Population

It’s a steamy summer day and John Stellberger is standing in a parking lot next to a reeking, oversized dumpster. He's staring at a series of fist-sized holes in the ground: rat burrows.

The dumpster is, in theory, closed — but barely; it's easy to see how an intrepid rat would gain access to the bounty inside. And for a rat, it's a bounty indeed.

"So they come out, they climb up, it smells of food," Stellberger said. "There's plenty of fresh stuff in here. They like fresh stuff, they don't like putrified stuff. Look at all the droppings."

Stellberger is founder and president of Environmental Health Services, a pest control company. He's an environmental health specialist — he does not use the word exterminator. He respects the animals he works with.

"They'll actually pull in plastic bags sometimes as a wind block in the winter, believe it or not, they make kind of a shield," said Stellberger. "I admire rats. They're complex, they're intelligent."

But part of Stelleberger's job is to kill rats. A few years ago, he stumbled on an innovative way to do that — one that's effective but also, he says, humane and environmentally safe.

Stellberger kneels over a rat burrow and starts pouring white chalk-shaped pellets into the hole from a plastic carton he took out of the back of his truck.

He's using dry ice — the same kind you might find in a a party supply store, or chilling a fancy cocktail.

Dry ice is just carbon dioxide in a solid form. Exposed to air it becomes CO2 gas, which is harmless on its own. But concentrated in a tiny confined space — like a rat burrow — it becomes lethal.

In other words, the rats asphyxiate.

Dry ice has been used for years as a means to humanely euthanize rodents used in laboratory research, and the American Veterinary Association endorses the method as being a more humane way to, if necessary, kill rodents.

Stellberger was an early pioneer in experimenting with using dry ice for wild, urban rats.

His work earned the blessing of self-described urban rodentologist extraordinaire Bobby Corrigan, who is probably the closest thing there is to a guru in the larger world of urban rodent control techniques.

"[It] basically replaces all the oxygen in the burrow," Corrigan explained. "The rats simply go into a kind of a sleep and they simply don't wake up."

Corrigan advises cities from Boston to Washington, D.C. to New York on rodent control techniques and is famous for his days-long rodent control "academies," in which he will instruct entire rodent and pest control divisions the best practices in smart rodent control techniques.

A couple of years ago, the city of Boston started employing dry ice to fight rats.

William Christopher, who heads the city's health and sanitation division, early on touted dry ice as a valuable tool in the city's efforts to control rat populations.

"We were actually one of the first to really start trying it, and it got really good notoriety," Christopher said "We promoted it, the concept of it, [and] other cities started using it."

Cities like Chicago, New York and Washington, D.C., began using dry ice too.

But then, in 2016, Christopher ran into a problem.

"One day we get a letter saying that we cannot use it," Christopher recalled, "because it does not exist on the insecticidal lists per the EPA."

The federal Environmental Protection Agency said that dry ice, despite being non-toxic and safe enough to put in a cocktail, was not an EPA-approved pesticide. So Boston and other cities had to stop using it.

That changed earlier this year, when a major scientific research company, Bell Labs, secured the first EPA-approved dry ice product — they call it "Rat Ice" — and now it's the only dry ice that's legal for cities like Boston to use on rodents.

Dry ice is, again, just solid carbon dioxide. And Rat Ice is just dry ice with an EPA-approved label.

"Basically it's not different than anything else," Stellberger said. "Just now, this layer of complications has been added ... We need to buy it from a local place that has become a recognized EPA establishment."

Stellberger had been purchasing his dry ice from a local vendor. Now, he says the only distributor selling EPA-approved dry ice is in Rockland, Massachusetts, about 20 miles away. And it costs about three times as much, he says.

Boston officials, meanwhile, have held off on using dry ice (or Rat Ice), hoping to negotiate an easier, less-expensive way of obtaining the material.

"It's a bit of a hassle. So I see where the city of Boston is coming from," Stellberger said. "But, you know, I'm just happy we can use it."

He's happy because, remember, he likes rats. If he has to kill them he wants to do it humanely. And he'd rather focus on teaching humans to be more responsible.

That is John Stellberger's larger mission.

As we pack up and Stellberger heads off to another site, he gets emotional as he talks about that mission, one he shares with rat expert Corrigan.

"I'd like to see some of this industry change to become kind of more preventive and more solution-based," Stellberger said, his voice catching a little.

"Our mission isn't to become pesticide sprayers, or just bait box checkers. ... Why do we have to kill things that we don't have to, you know?" he said. "We're better than that."

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