The sight is one that beekeepers say is understandably intimidating to the ordinary person out for a walk: a sliver of sky suddenly darkening amid the collective roar of thousands of honeybees before they cluster on branches or bushes.
In Britain, the behavior, known as swarming, typically takes place from May to July and is a natural process in which a honeybee colony splits in half and leaves with a queen bee in search of a new home. But the country is currently experiencing a greater numbers of sightings for this time of year, most likely thanks to unseasonably warm weather that followed a cold, wet spell.
As a result, beekeepers and pest-control workers who catch the swarms are reporting a surge in calls for their help as members of the public spot the clusters in backyards, in chimneys and even on barriers along city streets.
“We’re fully booked for the next four weeks,” said Rob Davies, a pest controller in Shropshire, in central England, who specializes in dismantling and rebuilding structures like chimneys to rescue honeybees, adding that he was getting “ridiculous” volumes of people calling for assistance.
Some of the bee rescuers are even having to order new equipment to keep up with the demand.
Although it is difficult to determine an exact figure for the current level of swarms, the British Beekeepers Association, which has almost 30,000 members, said that many were seeing more swarms than usual. Traffic for the association’s swarm removal site is up 19 percent compared with this time last year, said Ian Campbell, a spokesman.
“It’s their form of reproduction on a mass scale,” Mr. Campbell said of the honeybees. “But this year, it’s seemed to come a bit earlier. It’s seemed to come in force.”
Francis Ratnieks, a professor of apiculture at the University of Sussex, said that a recent stretch of sunny, drier days in Britain had created optimal conditions for honeybee colonies to split off.
“It probably means that we’re having half-decent weather for once,” he said.
Alan Deeley, a beekeeper in Warwickshire in England’s West Midlands, said the weather of preceding months was also a likely factor. Honeybee populations were strengthened last year by a long, hot and dry summer, he said, and then a period of cold, wet springtime weather that dragged through April meant that many beekeepers did not inspect their hives as frequently, for fear of exposing their bees to the cold.
“They were getting constrained in the hive, and that is a trigger for them to swarm,” Mr. Deeley said of the bees.
He said that he had received at least twice as many calls reporting swarms this year, and that beekeepers can sometimes stop a colony from swarming, including by increasing a hive’s capacity.
The bees have been drawing plenty of notice.
In Lancaster, a city in northwestern England, one swarm gained attention last week when it took a break on a metal pole on a stretch of sidewalk outside a real-estate agency’s office. (One commenter on a Facebook post pointing it out joked that they must have simply been browsing for a new home.)
On the island of Guernsey, a crown dependency that neighbors Britain in the English Channel, the swarms have been so numerous that Debbie Cox, the secretary of the local beekeepers association, recently ran out of the usual equipment and resorted to using a cardboard box to pick up a melon-size swarm that had nestled in a backyard apple tree.
“It’s almost like the bees all over the country have all decided this year they’re all going to swarm,” she said, adding the group had already received about 30 calls this season, compared with half a dozen last season.
Although honeybees are docile rather than aggressive when swarming, beekeepers say that people should still keep their distance if they spot a sizable cluster.
The insects are pollinators that perform a crucial role for biodiversity and agriculture, and concerns over declines in honeybee populations arose last decade because of the effects of pesticides and destructive mites, along with factors like fungi and viruses. Other bee species, including bumblebees, have also experienced ecological threats.
But the number of globally managed honeybee colonies has increased in the past 50 years, according to a longitudinal study published in the journal Nature last year, and beekeeping has boomed as a hobby in many places. Some beekeepers in Britain speculated that an uptick in hobbyist beekeepers was a factor in the recent increase in swarms.
And given that it is the start of the usual season for honeybee swarming, Professor Ratnieks said that if there was a surge, it was no particular reason for concern. “It’s just part of spring,” he said, “like birds building their nest.”
“If there is a lot of swarming, it really means the bees are doing well,” he added.