In my part of the world, swarm season is now. The air is full of ants, bees, and termites. Many of them are taking their nuptial flight and most are out scouting for a new home.
Backyard Bees will swarm when the hive becomes overcrowded and it is too warm inside for the entire colony to continue to coexist. The Queen will leave the hive with a group of worker bees and set up a new family.
This usually occurs in late spring/ early summer in most parts of the world.
Swarming is mainly a spring phenomenon, usually within a two- or three-week period depending on the locale, but occasional swarms can happen throughout the producing season. Secondary afterswarms may happen but are rare. Afterswarms are usually smaller and are accompanied by one or more virgin queens. Sometimes a beehive will swarm in succession until it is almost totally depleted of workers. Wikipedia: Honey Bee Swarming
You can tell that your honey bees are about to swarm if you see queen cups present and capped or an abundance of well-fed drones hanging around.
Bees will usually swarm to a tree, ledge, fence or box nearby while scouts go out looking for a new hive. A swarm will typically only stay in one spot for around 48 hours because they can only survive for around three days without eating again. A queen doesn’t get fed for a few days before the swarm so that she is in tip top shape to fly out. So, there is a sense of urgency for the bees to rehome their queen.