Bees may appear to be psychic in that they know what they are all up to within the bee colony. This communication is achieved through what is called ‘trophallaxis’. How this process works is through pheromones, as all bees produce pheromones and they pass them on whilst feeding. Bees feed each other, which is kind of cool I think, and as they feed each other they communicate. The whole bee colony is built around a queen bee and she produces special queen bee pheromones; which attracts the worker bees to her.
In winter, during the cooler months, the colony has contracted in size. The drone bees, in areas with severe winters, have been forced out of the hive during the preceding autumn. It is thought that they do this to conserve food within the colony. When the weather begins to warm up the bee colony will expand again by producing more worker bees. The queen is very busy laying all those eggs and eventually she will produce new drone bees.
The expanded colony or hive has become so large now that not all of the bees can access the queen. Her queen pheromone signal is not reaching those worker bees and so for them there is now no queen in the hive. This appears to be a psychic phenomena but is down to the pheromones. These worker bees are then compelled to create a new queen bee. This act will lead to the swarming of bees. The interesting thing is that the queen is essentially produced from the same egg as a worker bee. The difference, however, is that potential queens are fed ‘royal jelly’. Once the new queen bee has been created, she takes flight to mate with drones and get that valuable sperm inside her.
There can only be one queen bee in a colony and so the old queen will leave before the new queen emerges. She takes off with part of the bee colony and prior to their departure they all fill up on nectar. So, it this exodus of bees surrounding the old queen that we perceive as swarming bees. They fly in a clumped mass because all the worker bees are gathered around their queen. The queen is not a great flyer, probably due to her size and main function of laying eggs. Therefore, she needs to rest during the journey to find a new suitable spot to establish the colony. Thus, you get swarming bees settling on tree branches or some other structure.