Brian Weitz shops at Eastern Market and frequents other places on Capitol Hill. The Animal Collective member says he enjoys the area. “During the week, everyone goes to work and I have the neighborhood to myself.” (Astrid Riecken/For The Washington Post)

Two avocados. Dozen eggs. A bag of dates. Brian Weitz slips these groceries into a canvas tote emblazoned with teal bubble letters: ALL TOMORROW’S PARTIES CURATED BY ANIMAL COLLECTIVE.

Slung over his shoulder, it’s a souvenir from a music festival that his band helped organize in England last year. He’s in one of the most critically adored groups on either side of the ocean, but Weitz walks the aisles of Eastern Market unrecognized. He remembers being spotted here by a kid on vacation from Texas, once. That’s about it.

“We’re big in a very small bubble,” Weitz says. “But, yeah, I like the anonymity.”

And that anonymity is surprising, considering the blowout success of Animal Collective’s “Merriweather Post Pavilion.” Named after the leafy Maryland amphitheater that the band will headline Tuesday night, “Merriweather” was a triumphal gob of hallucinogenic pop music, crowned the best album of 2009 by Pitchfork, Spin and the Village Voice’s Pazz & Jop critics’ poll.

Acclaim riled the curiosity of the band’s already-ravenous admirers. Who’s behind this wondrous stuff? But Weitz, who first moved to Washington in 2004 to work on Capitol Hill, has tried to keep a certain distance, insisting that he and his bandmates are mere dudes.

“We’re just normal people,” he says, sporting the plaid shirt, jeans and sneakers to back that claim up. “But, at a certain point, you can’t hide who you are. Or the fact that I watch sports.”

Later, he’ll be watching “Project Runway” with his wife after a dinner of spinach pasta. (Homemade, hence the eggs.) It’s an easy walk back to his house near H Street NE, and en route, the 33-year-old ambles through Eastern Market’s North Hall, where dozens of toddlers have been released from their strollers for a weekly children’s music concert called Boogie Babes. Weitz says he likes to take his 2-year-old here sometimes.

The scene is chaotic, noisy and gleeful, not unlike an Animal Collective show.

Beginnings in Baltimore

When the band headlined Merriweather Post Pavilion for the first time last summer, the euphoria seemed two-fold. Facepainted hordes danced on the lawn, while the band members onstage played a dream-come-true gig. They grew up catching concerts here in the mid-’90s.

Around that same time, Weitz, Dave Portner and Josh Dibb first started crossing paths in the hallways of the Park School of Baltimore, an arts-friendly private school where Grateful Dead tie-dye was kosher with the dress code. Dibb introduced his pals to the band’s fourth member, Noah Lennox, during junior year.

By the summer of 2000, the core of the band had relocated to New York and began quietly jamming in a tiny Manhattan apartment. Weitz was studying at Columbia University, where he would earn a degree in environmental biology, and later, a master’s in public administration in environmental science and policy.

“It set you up for a career in the EPA or a government agency doing environmental policy work,” says Weitz of his graduate studies. “My goal was to do lobbying for conservation organizations.”

By 2004, Animal Collective’s reputation was bubbling, but the band members still needed day jobs. Other guys in the group earned their wages as record store clerks and art handlers. Weitz moved to the District for a fellowship working for the Senate subcommittee on oceans, fisheries and the Coast Guard, whose ranking Democratic member at the time was Massachusetts’s Sen. John F. Kerry.

Weitz would tour with the band when Congress was in recess. When he got home, he kept quiet about it.

“There were already articles in the New York Times about us dropping acid and stuff like that. I didn’t really want anybody Googling me. I was really, really paranoid about it, actually,” Weitz says. “I just didn’t want to lose the job. Kerry was running for president. He was the head of the subcommittee. I didn’t assume I’d be important enough for anybody to point me out, but . . . I don’t think the tolerance for taking LSD is too high on Capitol Hill.”

Even with his teenage psychotropic experiments long behind him, Weitz still didn’t want to jeopardize a career that had barely started. But when the fellowship ended in 2005, he dashed off to Seattle to record the Animal Collective album “Feels.” Then the band was offered a spring tour of colleges. Then some summer festival slots in Europe.

“It just never stopped,” Weitz says. “I’d ask myself, ‘What am I going back to? To put on a coat and tie? I’m 25. I don’t have a kid. I might as well just do this.’”

Based on friendship

Weitz stayed in Washington but hasn’t returned to the Hill. Animal Collective’s popularity continued to billow, peaking with the rapturous response to “Merriweather,” which the Village Voice described as so: “The people who liked ‘MPP’ liked it because it’s a musically progressive record with a generous outlook on life. (It really is that simple.)”

But life became more complex for a band that still seems uncomfortable with attention.

“Animal Collective — it was always based on our friendship,” Weitz says. “We’re not super social people. I don’t really go out that much. A lot of the guys in the band get social anxiety. We’re just kind of shy, and we’ve always been sort of a little insular unit.”

They’ve always used stage names. Occasionally, they perform in costume. Lennox is better known as Panda Bear. Portner is Avey Tare. Dibb goes by Deakin. Weitz was nicknamed Geologist by a friend who mistook what he was studying at Columbia. Onstage, he wears a miner’s headlamp.

“We always wanted our music to seem a bit mysterious and a bit detached from reality,” Weitz says. “To put on masks and have these names, it’s this loss of ego. . . . If we sort of turn off who we are in everyday life, we’ll feel totally uninhibited.”

Which might be why Animal Collective concerts have always playfully pushed toward delirium. There’s lots of instinctive improvisation and plenty of mush-mouthed singalongs, all anchored in puddles of sweet electronic goop. Portner and Lennox do most of the singing these days, while Dibb plays guitar and Weitz holds the fort behind a fleet of keyboards and samplers.

When they aren’t on tour, the band is spread across the planet. Lennox lives in Lisbon, Portner just moved to Los Angeles and Dibb resides in Baltimore, where the quartet recently convened to record their new album, “Centipede Hz,” a thicket of prickly digital textures pointed in the opposite direction of “Merriweather’s” gooey, feel-great melodies.

“We sort of cut ourselves off from people telling us what they want to hear from us,” Weitz says. “It’s always been more fun that way.”

And that casual/uncompromising approach has earned the band a devoted flock. Weitz describes Animal Collective’s most ardent followers as “really passionate,” which might be a polite way of saying “borderline obsessive.” They’ve drunk-dialed Weitz’s cellphone on New Year’s Eve. Others have shown up at parents’ houses. One hacked Weitz’s e-mail account.

But most interactions have been harmless, even sweet. Weitz remembers the shock of his first encounter with an excited fan. He was buying bagels in Brooklyn when the clerk blurted out a question about Animal Collective’s next gig.

Years later, Weitz was at a Williamsburg bar where Chris Taylor, bassist for the band Grizzly Bear, approached him: “ ‘I don’t know if you remember me, man, but I was working at this bagel place . . .’ ”

Engaging in his ’hood

One of the baristas at Peregrine Espresso, off Pennsylvania Avenue SE, is an Animal Collective fan, but he isn’t working today. Along with the teenage Texas tourist, Weitz says these are the only two people who have approached him on the streets of Washington.

“I love Capitol Hill,” Weitz says, drinking iced coffee on Peregrine’s front patio. “During the week, everyone goes to work and I have the neighborhood to myself.”

He didn’t always love it. After a Philadelphia childhood (he’s loyal to the Flyers), a Baltimore adolescence and his studies in New York, Weitz says he’s struggled to find his footing in the transience of Washington.

“I just decided if I’m going to be here, I should stop complaining about it and engage,” Weitz says. So he bought a house and signed on as investor in Toki Underground, the ramen shop on H Street NE.

“He’s just very polite, quiet and to himself,” says Erik Bruner-Yang, chef and owner of Toki. “But when he does say something, you should pay attention. . . . He understands the balance between doing what you love and trying to be able to make a living.”

Lately, maintaining that balance means afternoons holed up at home, working as Animal Collective’s manager, blasting out tour itineraries to fans on Facebook. Weitz says the gig is probably temporary — he doesn’t like it. “ ‘Hey, we’re gonna be in Seattle next Tuesday. Buy tickets,’ ” he says. “That feels weird.”

Also weird: The now-and-then happy hours and volunteer sessions he attends on the Hill, trying to stay up on the issues in case he ever decides to go back.

“When I have checked back in to do some volunteer work, it’s like, ‘Oh, my God. It’s 10 years later — the same debates about the same stuff,’ ” Weitz says. “On one hand, that shows that you need people fighting the good fight. But the personal sense of accomplishment you get from doing a show or doing a record, it’s addictive.”

For now, he’s fine with leaving the policy-wrangling to others while he strolls the desolate daytime streets of Capitol Hill.

“They play us in there sometimes,” he says out in front of Peregrine, nodding toward the cafe as he finishes a crumbling pastry. “One day, I was in here with my wife and I said something like, ‘Man, whoever is singing right now is such a Panda Bear rip-off.’ She started laughing and was like, ‘Are you serious? This is you guys!’”

He sips his iced coffee dregs.

“But I don’t listen to our music that much.”

Animal Collective performs at Merriweather Post Pavilion on Tuesday. “Centipede Hz” is out now.