What Are Sewer Rats? Meet the Norway Rat That Isn’t from Norway

When most people hear the word “sewer rat,” their skin starts to crawl—and for good reason. These creatures are more than just urban legends or cartoon villains. They’re real, they’re smart, and they’re thriving in cities across the United States. But there’s a lot more to sewer rats than meets the eye.

Let’s dig into the truth about these unwelcome underground residents: what they are, where they came from, and why they’re an increasingly serious problem in modern American cities.

What Is a Sewer Rat, Really?

The term sewer rat usually refers to the Norway rat (Rattus norvegicus), a species known for its impressive adaptability and close association with human environments. Despite their misleading name, Norway rats are not actually from Norway. Scientists believe they originated in northern China or Mongolia, spreading across the globe via shipping routes in the 18th century. The name “Norway rat” likely stems from a mistaken belief in the 1700s that they migrated to England from Norway—hence the misnomer stuck.

How Did They Get to North America?

Norway rats hitched rides on European trading ships during the Age of Exploration and colonization. As commerce expanded, so did the rats—making their way across oceans in cargo holds and settling into port cities. By the 1770s, Norway rats had established themselves in North America, pushing out the smaller and less aggressive black rat (also known as the roof rat).

Today, they’re found in nearly every U.S. city, particularly where dense human populations and waste create a perfect breeding ground.

Where in the U.S. Are They Found?

You may have the misconception that sewer rats are only found in older large cities like Chicago or New York. The fact is virtually every major U.S. city has a rat problem, but some are infamously worse than others. Cities with older infrastructure and high population densities are especially vulnerable. Notorious hotspots include:

Denver
Phoenix
Portland
Washington, D.C.
Seattle
Boston
Baltimore
Louisville

If your city is on Orkins annual “rattiest cities” list sewer rats are there!! Breeding in the sewer systems which provides the perfect nesting and foraging environment.

Yes, They Can Swim—and Even Come Up Toilets

One of the most disturbing facts about sewer rats is that they’re excellent swimmers. They can:

Hold their breath for up to 3 minutes
Tread water for up to three days
Squeeze through pipes as small as a quarter

This means rats can easily navigate city sewer systems, enter a structure through plumbing, and emerge through a toilet. They also exploit deteriorating, improperly installed, and damaged plumbing to get inside homes and businesses. It’s the stuff of nightmares, but for city dwellers, it’s an all-too-real occurrence.

Want to learn more? Check out our article on how rats swim up through toilets — you won’t believe what they’re capable of.

Why the Problem Is Only Getting Worse

Several factors are contributing to the growing population of sewer rats:

Urban Sprawl: As cities grow and more waste is generated, rats have more access to food and shelter.
Aging Infrastructure: Cracked sewer lines, abandoned buildings, and poorly maintained city systems create ideal rat habitats.
Climate Change: Warmer winters in many U.S. cities allow rats to breed year-round, accelerating population growth.
Human Behavior: Improper garbage disposal, outdoor dining, and lax pest control make urban areas more rat-friendly than ever.
Pandemic Effects: During COVID-19 lockdowns, rats lost access to restaurant waste and began aggressively invading residential areas. Many colonies grew bolder and more resilient.

What Can Be Done?

Cities are ramping up efforts to control rat populations with mixed success. Tactics include:

Pest control providers using new tools and technologies like The Sewer Assassin.
Using AI-powered smart traps
Upgrading waste management systems
Performing exclusions, sealing buildings, and repairing plumbing to prevent entry

But ultimately, the battle against sewer rats depends on long-term investment in infrastructure, public awareness, and consistent sanitation practices.

Don’t Ignore the Signs — Sewer Rats Are Closer Than You Think

Sewer rats may be part of the urban ecosystem, but their growing presence isn’t just gross—it’s a public health concern. These animals can carry diseases, damage personal property, and undermine city infrastructure. Understanding their behavior and origins is the first step toward controlling their spread.

So, the next time you hear scratching in the walls or see something suspicious in the toilet—remember, it might just be the infamous Norway rat, thriving in a city near you.