A rat ventures into a trash can at the corner of 15th Street NW and Vermont Avenue NW in Washington. (Michael S. Williamson/The Washington Post)

The District for years has been plagued by a growing mischief in its midst. Rats — the four-legged, bewhiskered kind — have been spotted roaming the streets, scurrying across alleys and eating their way through trash cans.

On Monday, a rat made its way onto the White House lawn.

“I am standing in our @FoxNews standup location on the @WhiteHouse North Lawn and notice in my peripheral vision something moving at my left foot,” tweeted reporter John Roberts. “I assumed it was one of the ubiquitous WH squirrels. But no . . . it was a big brown rat.”

It was perhaps one of the boldest moves a rat had made since a rodent that became known as “Pizza Rat” was seen gorging on a slice in New York. (The original “Pizza Rat” may have been trained to be so bold by eccentric New York artist Zardulu, though other, equally hungry rats have been spotted in Manhattan since.)

Social media speculation over the rat’s identity and motives ensued. People wondered: Was it looking for a job? Fleeing a sinking ship?

Unlikely.

According to the District’s resident rat guru, Gerard Brown, a program manager at the D.C. Department of Health, it was probably one of many rats “flushed out” of its burrow by heavy weekend rain.

“Water doesn’t kill them or reduce them at all — rats can swim for as long as a week — but what it does do is make it difficult for them to find food,” Brown said. “That draws them out, too.”

Rat sightings correlate with a number of factors, Brown said: food sources, weather and population density.

Recently, Washington has had a perfect storm of all three, Brown said, with mild winters and booming development bringing more people, and trash, into the District.

On Jan. 1, an additional $906,000 the city allocated to help the Department of Health get a handle on the District’s rat problem will kick in. Brown said the money will be used to hire staff and equip exterminators with mobile devices that use geolocation data to track rat complaints in real time, among other things.

“Technology is evolving into rodent control,” he said.

Calls about rodents to the city’s 311 line reached an all-time high in 2017, according to data collected by The Washington Post, totaling 5,310. That is a 50 percent increase from 2016.

By the end of this year, the numbers will likely mirror those from 2017, Brown said.

Residents and visitors are encouraged to call 311 to report rat sightings so the city can keep track of which areas are most affected. Brown said the city has not received any reports of rats on the White House grounds in recent years.

The White House and its neighboring park, Lafayette Square, are maintained by the National Park Service, which conducts rodent sweeps weekly.

Park Service spokeswoman Jenny Anzelmo-Sarles said recent rat activity near the White House has not increased.

“Rats are very much an urban challenge,” she said. “We haven’t seen a change, or a need for immediate concern, around the White House.”

Over the past several months, calls complaining about rodents in the vicinity have been sporadic.

In mid-October, a call to 311 reported rats in the 1400 block of F Street NW, according to District records. About a month earlier, a caller identified rodents in the 1500 block of Pennsylvania Avenue NW, just feet from the White House’s front gate.

Last winter, open government advocate Alex Howard took video of a vulture feasting on a dead rat on the sidewalk just outside the White House grounds.

Brown said the city’s rat offensive, which includes sterilization and extermination, will kick off in Ward 1 next year and work its way through each ward in numerical succession.

Petworth, Columbia Heights and Capitol Hill are among the areas with the most rodent reports, according to city data. But that does not mean other areas have been spared, Brown said.

“Every human in D.C. comes within five feet of a rat every single day,” Brown said. “They just may not always know it.”