Because there was a swarm in WC’s next-door neighbor’s backyard.
This swarm of honeybees turned up yesterday in a big cloud of bees. They overnighted in this giant clump, presumably with their queen in the center. They hung around until about 1:30 PM, and then left, headed northwest in a very impressive cloud.
It’s normal behavior, when a queen and some of the workers split off from an existing hive. But it’s the first time WC has seen it, let alone in his backyard.