Beekeeper Christie Ray arrived at the scene and was stunned. She knew a swarm of honeybees had escaped after a truck overturned on a Texas road, but nothing prepared her for what she saw.

About 20 million bees were flying in groups so large they resembled dark clouds. So many sat on a tree branch that it broke. The air smelled like honey, beeswax and bananas, the odor bees release when they sting.