One swarm covered the side-view mirror of a Volvo station wagon in a lot by the Hudson River, trapping a family of three inside. Another humming cluster the size of a watermelon bent a tree branch in front of a Chase Bank on the Lower East Side, attracting a crowd of gasping onlookers. And for several hours, thousands of bees carpeted a two-foot-tall red standpipe on the patio of a South Street Seaport restaurant, sending would-be outdoor diners elsewhere.

This spring in New York City, clumps of homeless bees have turned up, often in inconvenient public places, at nearly double the rate of past years. A warm winter followed by an early spring, experts say, has created optimal breeding conditions. That may have caught some beekeepers off guard, especially those who have taken up the practice in recent years.

When Happy Miller, the Seaport restaurant manager, saw tourists flailing their arms in a cloud of airborne black specks late last month, he closed the glass door and quietly panicked.

“Oh my God, what do I do?” he thought before calling 311, security guards and local news outfits. The television trucks, he said, were first to arrive. It took several hours before Officer Anthony Planakis, the New York Police Department’s unofficial beekeeper in residence, arrived with a metal swarm box and a vacuum to collect the 17,500 or so homeless creatures.