I've been watching my 3 weakest hives closely, all very late season swarms, hoping they would pull in enough stores for the upcoming winter. Thinking / hoping I was helping them accomplish this, I've been feeding them using boardman feeders stuck right in the hive entrance. Several of you warned me about the danger of robbing this type feeding could cause. Well today I have seen that happen first hand. I was installing my mouse guards on my hives as part of my winter prep and entrance reducers on the 3 hives I've been feeding. As I got to my 3rd hive, I noticed an unusual amount of activity with pollen being brought in and many more of the ladies coming in without anything obvious. I installed the mouse guard without any problem and moved to hive #4. The first thing I noticed, and what hinted that something was wrong, was several yellow jackets flying around the entrance and in fact landing and going inside. I killed several that landed on the boardman feeder while watching the large amount of bees going in but without any pollen of any kind. It finally hit me that this hive was being robbed! Last Thursday this hive weighed, in my guesstimate, about 30 pounds. When I lifted it this afternoon, it may have weighed half that. I took the top and inner cover off and the deed is almost done. Very little of anything is left as far as stores or nectar / honey / sugar water. I stepped away from hive #4 and looked back toward hive #3, the sunlight was just right to see the bees leaving hive #3 and flying directly to hive # 4 and vice versa. I went on to hive #5 and # 6 and installed the mouse guard or entrance reducer without anything out of the normal observed. I stood and watched the bees fly between hive #3 and # 4 for sometime. I tried to take pictures and videos but looking into the sun none of them are usable. Bummer about that but I will never forget that scene. Lesson learned but the bees made the decision for me. I was going to combine the hives after frost so they have saved me the trouble of doing so, kinda anyway.