One point of view:

Which bees go with the swarm and which stay behind is a question that has long exercised the minds of beekeepers. First it was thought that the old go and the young stay. This was shown to be wrong. Then it was thought that the young bees go and the old stay, as this would explain why the bees of the swarm do not return to the old site, not having flown from it sufficiently to be familiar with it. This now has been shown to be wrong too. Separation of the bees capable of homing from the non-homers does not give the division that actually occurs in swarming. 

Moreover, it has been shown that reorientation to a new hive position can be induced in any bees by confining them there for a time. At present it looks as if the selection is a random one, at least in the case of swarms from crowded colonies. Absconding swarms, reproductive swarms and stocks deprived of hives and combs all behave in an identical manner once they have 'decided' to swarm. With the colony deprived of its combs the decision is made for it. Absconding swarms and colonies deprived of hives and combs consist of all the bees that can fly. This shows that there is nothing very distinctive about the bees that go with a swarm. 

The proportion of bees that leaves as a swarm appears to depend on three things : the degree of crowding, the size of the colony and the amount worker brood and number of queen cells. The more crowding, the higher is the proportion of bees that leave with the swarm. In fact in colonies artificially crowded to an extent not normally met with, as many as nine tenths of the bees may be found swarm. The effect of the size of the colony is, perhaps unexpected. Although big swarms come from big colonies, it is from the little colonies that greatest proportion of bees go with the swarm.

Swarming of Bees Bulletin No. 206 H.M.S.O. Bulletins Ministry of Agriculture, Fisheries and Food

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