Hmm, regarding empty supers and heat, here's one I've been known to do
on the opposite end.  I had a hive that was getting a lot of bees hanging
out on the front of the hive during very hot weather (enough that my first
thought when I saw them was "oh no, a swarm!") and realized it had a lot
to do with hive temperature, as they would only do this when it was VERY
HOT and still weather.  So I put an empty shallow super on the top of
the hive (no frames) as a heat trap.  Voila!  No more clustering on the
front of the hive.  Yes, I took it off at the onset of cooler weather.
 
Jane B.  [[log in to unmask]]