In the spring there is plenty of food for bees so their colonies grow rapidly and likely will get to the point where the whole colony can reproduce. It will split in two and the queen and more than half of the bees will leave as a swarm to find a new home. Meanwhile a new queen is being raised at the original location so that colony can continue.
The swarm that leaves doesn't know yet where it's going to live. These 15,000 or so bees will form a big cluster on a nearby branch while they send out scouts to find a new homesite. They have about 24 to 48 hours to find a home. A perfect home would be a hollow tree 30 feet in the air. Those are really hard to find so they will move into just about any enclosed space of appropriate size. This can include a garage wall or a wine barrel or even a cardboard box!
We prefer to rescue the swarm of honey bees while they are still in a cluster on the branch since it's easy and it gives them the best chance of survival.
Visit our YouTube channel to see some fascinating swarm rescues! https://youtube.com/@kingsburghoney2022