The reason is simple: People feed them. Monkeys are the living representatives of the cherished Hindu god Hanuman, and Hindu tradition calls for feeding monkeys on Tuesdays and Saturdays.

Dr. Tyagi expressed impatience with residents who feed the monkeys one day, then complain to the city when the monkeys steal their clothes on another day.

Dr. Tyagi’s agency has asked the city’s wildlife agency for help, but wildlife officials claim that the monkeys — a scourge of the city for years as urbanization has encroached on their original habitat — are no longer wild and are thus not their responsibility.

“This problem will never be solved” as long as Hindus feed monkeys regularly, said R. M. Shukla, the city’s chief wildlife warden. “We’ve issued many ads asking people not to feed monkeys in public places.”

In 2007, a Delhi deputy mayor died when he fell from his terrace after being attacked by monkeys, a widely publicized episode that spurred the city to step up its efforts to move monkeys to safer environments. Yet such attacks continue. This month a 14-year-old girl was seriously injured when she fell from the roof of a five-story residential building after monkeys pursued her.

“Monkeys do commonly bite people, and their bite wounds can be extensive,” Anthony S. Fauci , director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md., wrote in an e-mail. “They are smart enough to often attack the face of the person.”

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While monkey bites can lead to rabies or a fatal form of the herpes virus, documented cases are “close to nonexistent,” Dr. Fauci wrote. Skin bacterial infections from bites are common, however. They are treatable with antibiotics .

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Stories abound in Delhi of monkeys’ entering homes, ripping out wiring, stealing clothes and biting those who surprise them. They treat the Indian Parliament building as a playground, have invaded the prime minister’s office and Defense Ministry, sometimes ride buses and subway trains, and chase diplomats from their well-tended gardens .

Roopi Saran, a Delhi resident, has seen monkeys steal candy from the hands of her children. And tribes of monkeys often take over her yard, preventing her and her children from venturing outside.

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“So we sit inside our house like caged animals, like we’re the ones in the zoo and they’re the owners outside looking at us,” Ms. Saran said.

With the city’s trapping program a failure, some residents are getting a bigger monkey, a langur, to urinate around their homes. The acrid smell of the urine scares the smaller rhesus monkeys away for weeks. But the odor is no bouquet for humans, either, and as soon as it disappears, the rhesus monkeys return.

Amar Singh, a langur handler, was sitting across the street recently from one of his langurs in Delhi’s diplomatic neighborhood while his monkey systematically stripped the leaves off a tree in the yard of well-tended home. The langur, a large monkey with a black face dramatically framed by white fur, was tied to a pole with a six-foot leash. Mr. Singh cautioned against getting anywhere near the animal because “a langur’s slap is so hard, it can send its target back by five feet.”

Mr. Singh said that he had 65 langurs urinating on prominent homes and buildings throughout Delhi. He and his partners feed and walk each monkey during the day, but they remain tied to their posts overnight. He charges about $200 a month.

Dr. Tyagi said langurs simply pushed rhesus monkeys to ransack adjoining homes. The city started out seven years ago paying monkey catchers $5 for every rhesus monkey they caught. It raised the price to $9 four years ago, and now pays $12.

“Despite offering this rate, there are few monkey catchers,” he said.

Years of trapping, using cages baited with fruit and nuts, have taught the monkeys to avoid the traps. For a time, the city hired highly professional trapping teams from the south of India, but even they have stopped coming to Delhi, Dr. Tyagi said. Himachal Pradesh, a northern Indian state, issued permits to kill monkeys that destroyed crops, but the practice spurred protests and is not being considered in Delhi.

Trapped monkeys are brought to a sanctuary in the south of Delhi, but residents who live near the sanctuary say their lives have been ruined by the influx. Monkeys easily scale the sanctuary’s walls and often find their way back to Delhi’s central neighborhoods.

Kali, who lives in a small hut near the sanctuary and goes by only one name, said her young daughter and niece had both been bitten twice, requiring trips to the hospital and expensive vaccinations . After being attacked while bathing, she now asks her husband to stand guard when she washes. And for a poor family like hers, the monkeys are a constant threat in more ways than one.

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“I give them my leftovers like roti,” she said. “But then they ran away with my onions.”