Across the city, delis and bodegas are a familiar and vital part of the streetscape, modest places where customers can pick up necessities, a container of milk, a can of soup, a loaf of bread.

Amid the goods found in the stores, there is one thing that many owners and employees say they cannot do without: their cats. And it goes beyond cuddly companionship. These cats are workers, tireless and enthusiastic hunters of unwanted vermin, and they typically do a far better job than exterminators and poisons.

When a bodega cat is on the prowl, workers say, rats and mice vanish.

That is the case at a narrow corner store in Williamsburg, Brooklyn, where a gray long-haired tabby named Halloween goes on regular patrols when she is not lounging on a plaid bed tucked behind dusty rows of Schweppes ginger ale and empty cardboard boxes.

“In the morning she is lazy, it is her nap time,” said Urszula Jawor, 49, the deli’s manager, a Polish immigrant who smiled with motherly pride at Halloween, adding that the cat was named for the day she wandered in off the street and claimed the Bedford Avenue store as her home.