Consider the rat—specifically the Norway rat, which doesn’t come from Norway. It is brownish gray and as long as 16 inches. During its year-long lifespan a female can produce up to five litters of seven babies, although litters can be as large as 14. It has excellent sight and hearing and an acute sense of smell. It can swim across the Charles River.

It thrives in cities all over the world. Here it lives in burrows in the Boston Common or wherever it can find suitable soil near people. Some of Boston’s best addresses are the most infested. Rats carry salmonella and rabies. About 50,000 Americans are bitten yearly by rats.

Rats can live in your house, as several did recently on Hancock and Myrtle streets on Beacon Hill. Andrew Christoffels, who works at Charles St. Supply, heard from the residents that the rats were in the toilet.

I’m betting you don’t want them in your house. The city helped the Beacon Hill residents with their problems, said John Meaney,  director of the city’s Environmental Services.

Many Boston residents, however, are at risk from rats moving in. We live in old buildings with holes in the foundations and improperly sealed pipes.

Rats can crawl through a hole about the size of a quarter, said Missy Henriksen, vice president of public affairs for the National Pest Management Association near Washington, D.C. NPMA estimates there is at least one rat in every American city for every person in that city, she said, although no one has an exact count. She said her association held its annual meeting last fall in Boston, and Meaney spoke to the group.

Henriksen said Meaney and his team appear to be doing a good job tackling Boston’s rat problem. Eight inspectors are licensed to carry out rat control, said Meaney. The number of people who know Chris and Pedro by their first names indicates how many neighbors have regular dealings with those downtown rat guys. But they could do with help.

Rats need food, water and shelter. Boston residents readily provide the food. You know who you are.

You’re the one who sets your trash bag with food in it on the sidewalk the night before pickup. Rats get in, and the bag starts moving. Food splays onto the street, and that attracts more rats.

Restaurants exacerbate the problem if they are careless with their food disposal and don’t keep their barrels clean. But recent new regulations have improved restaurants’ behavior.

Anne Pistorio, who lives in the North End, is a reluctant and disgusted expert on rats. She walks twice a day and sees them everywhere. Pedro’s diligence, she said, has made a difference in her neighborhood at reducing the rat population.

But it’s not only restaurants and the sorry food disposal practices of residents. “Dog waste is to rats what fuel is to fire,” Pistorio said. She estimates there are about 1,000 dogs in the North End and too few owners pick up after their dogs, leaving rats to feast on the feces. Yuch.

The mild winter we had last year didn’t help reduce the population. The growing popularity and proliferation of food trucks worries her.

If you have rats, it’s hard to tackle them on your own. Meaney said new pesticide regulations have made it harder for homeowners to bait burrows. And it’s true: my local hardware store no longer carries rat poison. So the city or a private pest control company is your best bet now.

If it makes you feel better, some cities have it worse. Baltimore had an explosion of rats in the past few years. Washington, D.C. had a kerfluffle last year over a new wildlife law sponsored by a city councilwoman that seemed to imply that rats couldn’t be killed, but instead had to be relocated. Virginia and Maryland said, “No way.”

As problematic as some Bostonians have found rats to be this year, there may be good news. This winter we’ve had a few zero-degree days. Some rats who haven’t found there way into someplace warm, like your basement, will die. Meaney said that Big Dig construction replaced sewers so there are fewer holes in downtown Boston where rats can enter. His crew constantly monitors popular rat locations.

Meaney said rat calls are slightly down, Henriksen confirms the situation might be better. Pest control is a 6½ billion dollar industry, she said, but from year 2010 to 2011, revenue for rodent control declined about four percent.

Trash is key. Meaney said the rat population in Beacon Hill and the North End would decline if trash pickups were reduced to two days a week, a schedule both neighborhoods are reviewing. He believes if people were required to place trash out only on the morning of pickup, rats would go elsewhere to find food.

Meanwhile, he said, call the hot line at 617-635-4896 with rat sightings. Pay attention to where the rat goes—into a catch basin, a yard, toward a food supply? To be successful at getting them he said, “You have to think like a rat.”