I've seen a tree that had three large (~8in/20cm) balls of bees hanging off of branches. My grandfather (a beekeeper) said the queen had likely stopped at each spot to consider it for a hive (leaving pheromones), then moved on, and the swarm landed at each place. He was greatly entertained at the idea that the bees on the outside were trying to get to the queen (who wasn't there) and the bees on the inside had figured that out but couldn't leave because of the bees on the outside.
That said, my grandfather was a beekeeper and a father is a beekeeper and I'm a little uncertain about how much of their hobby is built on communal agreement, anecdotes, and personal experience as opposed to scientific data. (The same can be said about our profession though - what was the last good study on code readability you read vs the opinions on code readability you have?)