What you saw may have been usurpation.
Here is an article from Dr Mangum about it. He saw it and photographed as it happened. He was able to market the new queen before she entered the hive ans was able to determin that the new q was the surviving q after it was all over, three days later. He talked about it at the bee college in Tampa last year.
Usurpation: when one colony takes over another
In the December 2010 issue of American Bee Journal, Dr. Wyatt A. Mangum describes the phenomenon of honey bee usurpation—the taking over of a healthy colony by a summer swarm. Mangum not only describes this unusual behavior in great detail, but provides photographs as well.
Until recently, usurpation sightings have been limited to Africanized bees taking over colonies of European honey bees in the southwestern United States. However, Mangum’s usurped hives are located in Virginia and the resulting colonies did not show any of the aggressive behaviors typical of Africanized colonies. Instead they were “normal” colonies with average European honey bee traits. According to Mangum, other occurrences of usurped hives have been recorded in nearby areas of Virginia and North Carolina.
According to the article, usurpation works like this:
A summer swarm invades an established colony.
Fighting between bees is evident.
The queen of the established colony is killed by the invading swarm.
The usurping queen eventually becomes accepted and begins laying eggs.
The summer swarm, which under normal circumstances could not survive the winter, overwinters on the stores collected by the usurped colony.
In the first usurpation that Mangum documents, the entire process—from the arrival of the swarm until the invasion was complete—took 18 minutes. If this is typical, the process may be more common than we realize. From the outside, at least, the invaded hive looked no different in the evening than it did the previous morning. On the inside, things were unsettled until the old queen was dead and the new one was accepted—a process which took three days.
Mangum cautions that it is extremely difficult to distinguish between a normal supersedure and a colony usurpation just by looking at the queen, so one should not jump to conclusions. However, the possibility of usurpation casts a different light on the survivability of summer swarms.