I am a home beekeeper with 1 hive in the city.
 
September last year my bees were Ok.  In October after sunset and on until
midnight, many bees were attracted to the house, crashing into the windows,
appearing to be attracted to the inside (incandescent) lights.  In the AM
for about 10 days running, there were hundreds of dead bees below each
previously backlighted window.
 
By the end of November, the entire hive had crashed.  No evidence of
disease, no piles of dead bees in hive, no apparent problem with Varroa,
though previous history with other colonies in previous years at another
site.
 
Has anyone seen this or have any ideas on what was going on with this behavior?