Just had the same thing happen to my hive!!! Lots of dead worker bees, think it was a case of robbing. I think I may have caught it early enough to stop the complete desturction of my hive. I blocked the entrance this morning and left only a small gap to allow the workers to exit. This afternoon there were lots of Drones trying to enter the hive but the entrance was to small to allow them inside. They just covered the outside of the hive and then slowly they all flew away or just droped to the ground and died. Not to sure what to do next?