In my opinion this is one of the coolest things that bees do. Partially because a swarm is a highly visible and spectacular display of bee behavior. But mostly because free bees are awesome. Basically, swarming is where the queen bee leaves the colony and takes about half of the population with her. The queen flies away with half the colony and goes out into the world to find a new home.
Swarming is how a honey bee colony reproduces itself. Typically in the spring the queen bee will begin to dramatically increase the number of eggs laid. the number of eggs laid is directly correlated to the increase in resources being brought in from the outside world by the forager bees. Eventually the number of bees in the hive becomes so abundant that the colony begins the process of swarming. The genetics of the bee colony and the number of available resources will determine how likely a colony is to swarm.
Inside the hive the process of swarming begins with the formation of a new queen bee. The worker bees begin to create swarm cells where a new queen bee will be raised. Swarm cells are usually on the bottom of a brood frame pointing downward. These cells in the picture are actually emergency queen cells. Deep inside the larger queen cells are larva which are being fed an exclusive diet of royal jelly.
Eventually the swarm cells will become capped which is a sign that the colony is very close to swarming. Other signs as well will indicate that a colony is thinking about swarming. In the spring you will also see a huge increase in the number of drone cells. The drones are required to fertilize the new queen so we need plenty of them around.
Then eventually the day comes where the original queen will leave the hive. For several days the nurse bees have been restricting the diet of the queen and running her around the hive. The queen must be loose body mass for her upcoming flight. Usually the same day that the new queen will hatch the original queen leaves the hive. The queen will fly out and approximately half of the hive will leave and follow her on the journey.
The queen lands so that the colony can rest for a short period of time. The group of bees that left with the queen will surround her and form a huge scary looking ball of bees. A hanging swarm looks scary and intimidating but in reality they are very unlikely to sting and just need a place to organize. It is in this condition that the bees can be transported and moved into a new hive.
While hanging from a high tree branch or small shrub there are hundreds of scout bees looking for a new home. It can take hours or sometimes days for the scout bees and the colony to agree on a new home. It is during this period of transition where a bee keeper can quickly swoop in and give these bees a new home. The swarm is either shaken into a box or the tree branch can be cut. The bees are transported back to the bee yard in a box and the colony can be introduced into a new hive body.
For a bee colony, swarming is an incredibly dangerous and counter-intuitive behavior. In the spring the colony is a safe and productive environment. Hundreds of bees are hatching every day and resources are pouring in. The hive is functioning at it’s best and only getting more productive. Then suddenly the queen decides to leave and flies into the big dangerous outside world. Putting herself and the original colony in potential jeopardy. But this behavior is required for the genetic distribution of the species. Just as plants devise methods of dispersing seeds long distances, the honey bee evolved behavior to spread their genetics as well.