Bee swarms can be kind of scary. If you see a swarm, don't worry.
The swarm is mostly harmless and is unlikely to attack unless they feel under attack, this can happen with a lawn mower or other power equipment. Never attempt to kill the bees in a swarm, Honey bees are very helpful to the environment. Swarms can relocate very quickly, this one moved within a few minutes. When you see a swarm, the original hive should be close nearby. Call a local beekeeper and if it's spring time, they'll usually come remove them for free, relocating them to a safe place. Spraying a mixture of flowers and sugar can calm the bees down without harming them. If you can't cut the branch off of the tree, or don't have any other method, you can shake them into a box, or bucket to transport elsewhere.
However, doing it this way will make most of the bees take flight. You will then have to repeat the process a few times as they return to the area. To make them stop returning to the area, spray vinegar on it to prevent them from sensing the Queens Pheromones. Make sure the boxes ect are completely sealed, if there's a way out they'll find it.
Swarming is the natural way that the hive reproduces itself. For honey bees to survive, they have to have a specific population in it's hive.
There can be tens of thousands of bees in a single swarm.
The hive prepares for the swarm many days in advance.
They stop feeding the original Queen and start making Queen Cups to create more queens.
Once the swarm leaves the original hive, they find an area to congregate to prepare to move, usually in a nearby tree.
Scout bees are then sent out to find the best location to build a new hive. These scout bees are usually very familiar with the surrounding area. If there isn't anything nearby, they will search for almost a mile. When the scouts return, they do a waggle dance to show their enthusiasm about the location they found.
Based on how hyperactive they are, the other Scout bees go to the location to see for themselves. When they return, they give their opinion of the location by how hard they shake it. This continues until it is clear which location the scouts prefer. Then the Queen and the entire swarm will move to the new location. The swarm will usually be gone in 1-3 days. If they don't, they can starve to death. If the Queen is lost for any reason on the flight to the new location, the entire hive will perish as they won't be able to create enough members to survive.
Utah Bee Removal Specialists: