However why did they swarm when they did?  Just get overcrowded
late in the
game, or is there a problem (mites?) that makes them act odd?
 
-Mike
 
I haven't found any sign of mites yet.  The colony started out in the
spring as a split.  It was doing quite well, by late august it had filled
two shallow supers. Interesting enough the day I went to pull the
honey was the day I found the swarm.  They took enough of the honey
with them that I didn't dare remove any of the remaining honey from
the old colony.