Much has been written about so called 'late swarms' that get reported every year for as long as I care to remember. Before it was all about "I say she say" sort of an affair and not many of the beeks would believe what I have been writing/telling them for years.
As of late, this occurrence was observed and later studied, so now the scientific community agrees and supports what was before only anecdotal evidence at best...
Bees, for one reason or another, usualy only known to them, know that their survival through winter is in question and they collectively decide to leave the hive and join up with another (usualy with mutual consent, as it were) Cause for such a move can be loss of queen, new virgin queen, sickness of one sort or another, bad smell in the hive, unpleasant medicines, mouse pee and all bunch of other things that could disturb the hive to such a degree that they see no other way but to abscond.
Absconding, such as it in reality is has been noticed by very few beeks and in most part only swarms are seen. So called swarms are reported, discussed with peers and nothing further is done about it. Departing bees usualy enter the new home within minutes and nobody is the wiser.
In the countries of Europe, where bees are kept in bee-houses and hives are tightly stacked side by side and 3 rows high, such exodus is more often than not done on foot and at night. They simply depart, walk over to the new hive and enter. No fighting and no fuss is evident or reported. That is why I say that all affair, strange as it may seem to us, goes largely unnoticed.
Strange but true my friends. . .