A pair of brown rats sniffs for mischief. Heiko Kiera/Shutterstock.com

An urban rodentologist explains how to defeat the sneaky vermin.

Dear CityLab: Rats are gross, for sure. But are they actually dangerous, or just disgusting?

In addition to possessing those spooky tails and beady little devil eyes, the vermin actually do pose a significant threat to your health and home. For starters, they can transmit 55 to 60 different pathogens, including Salmonella, E. coli, and the Ebola-like hantavirus.

Rats can also carry lice, mites, and the fleas that spread bubonic plague. They’re the “reservoir” for the disease, infectious disease specialist Michelle Barron from the University of Colorado Hospital explained to CBS News. Of course, outbreaks are rare—we’re not even remotely close to the epidemic scale seen during the Middle Ages—but a Denver-area teenager died from the bacterial infection earlier this month.

This map from the Centers for Disease Control and Prevention charts plague cases from 1970-2012. They’re largely clustered in the Southwest, where the bacteria is common in prairie dog colonies, Barron said.

CDC

And let’s not forget the dreaded rat bite. The critters have been known to attack babies and homeless people, when they’re attracted to food residue on or near people’s skin. Humans can get the aptly (and horrifically) named rat bite fever this way—or just by handling an infected rodent.

On the other hand, rat bites are fairly rare in cities, and the risk of disease is very low. “City rats are not becoming more ‘brazen’ towards dogs, cats, or people. When they get a little too close to people, it is usually because they don’t see the person very clearly and can’t tell the person from a tree or some other vertical object,” explained a pest control expert in an AMA-style chat hosted by the Washington, D.C. Department of Health.

If rats have settled in underneath your home, you’ll need to worry about the building’s structural integrity. Rats move a lot of dirt when they burrow, potentially causing the foundation to shift and crack. Urban rodentologist Robert Corrigan says he’s seen statues leaning in parks because of rat burrows beneath them.

Rats love chomping on wires, says Corrigan—which is bad news for your home’s gas and electrical setups. When the rodents chew through wires, they can cause short circuits, fires, and explosions. The critters’ powerful, constantly growing incisors allow them to feast on just about anything. The word rodent, after all, comes from the Latin rodere, meaning “to gnaw.”

Is my house overrun by rats?!

Don’t believe everything you read about high-profile infestations, like the ones reported at Brooklyn’s Barclays Center or at a Manhattan KFC/Taco Bell. Corrigan says that in many cases, someone will witness 8 to 12 rats running out of a space and perceive them as “hordes” of hundreds or thousands. A follow-up inspection often reveals far fewer rats; it’s just the ick factor causing us to overestimate the population. Rats “just don’t build up like that, in those numbers,” says Corrigan. “You’d have to be in a very unique situation.”

“If you see one, and you only see one again over the next couple days, chances are very good it’s one,” Corrigan adds. But if you spot rats of different sizes and ages, you might be dealing with a whole family of rats in your home.

What can I do to keep them away from me and my house?

Clean. “These animals need food,” says Corrigan. “There’s no mystery here.” A full-grown rat can eat more than three ounces of food in a night; younger ones eat about an ounce. If you eliminate their food sources, you should eliminate the problem.

Never leave food out in the open where rats can get at it. The New York City Department of Health also recommends that you keep trash in sealed containers, take garbage cans to the curb as close to pick-up time as possible, and wash the cans periodically. Gross fact: Rats eat feces, since it contains a lot of undigested food, so be sure to deposit dog poop in a separate bag in the trash can.

Seal off entry points. Rats are flexible enough to squeeze through half an inch of space. Install door sweeps, metal thresholds, and kick plates to make outside-facing doors flush with the ground. Check for cracks and holes in every area of your home, and seal the gaps with caulk, roofing cement, or (for large holes) metal screening. Corrigan recommends conducting regular walk-arounds so that you know your property inside and out.

If I do have a rat problem, how do I get rid of them?

First of all, don’t try to fix it yourself. Even if you’ve dealt with mice before, don’t expect that you can handle a rat problem on your own. “I’m not sure I would leave a rat job up to any homeowner,” says Corrigan. “They’re too wily, they’re too cunning.” If you own your home, call an exterminator. If you rent your place (and your landlord isn’t doing anything about the problem) or you see rats on another property, call 3-1-1 or your local DOH. Some cities, including New York and Chicago, allow you to file a rat complaint online.

Treatment starts with removing any food sources for rats. Then, pest professionals have two main tactics at their disposal: traps and rodenticides. Most rodenticides kill rats by causing internal bleeding, and Corrigan says they pose limited toxicological danger if used correctly. However, if you’re worried about rats dying in wall voids or other inaccessible areas, you’ll probably to have to stick to trapping.

Despite her stealthiness, Fluffy is no match for a rat.
(Axel Bueckert/Shutterstock.com)

If you want an exterminator to capture your unwanted houseguests alive and spirit them away to, say, a wooded area outside the city, that’ll cost you: Most pest professionals are paid by the hour. Plus, bear in mind that born-and-bred city rats might not fare well in the “wild”—and they may not get a “humane” death after all.

You can’t really just sic your pet on them either, says Corrigan. Some of the worst infestations he’s ever seen were under doghouses (remember, rats are drawn to feces). Rats can adapt to the presence of a pet, feeding while the dog is asleep. And contrary to popular belief, rats are not easy prey for cats. Corrigan says most cats have learned to view a full-grown rat as a force to be reckoned with. A 2009 study showed that cat predation had relatively little impact on the size of the rat population in Baltimore. Cats killed rats only occasionally, and primarily targeted the more manageable juveniles.

“The most humane method to control rodents is not to let them inside in the first place,” Corrigan says.

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