I have posted a couple of pictures to show what "my bees" look like and a "stranger bee" that I have seen at the hive entrance. I am pretty sure these are robbers but I am curious if anyone can tell me the race of the bee or if it belongs to some "generic" race of ferile bees. In case it is not clear in the photos, the stranger bee has noticably less hair on its thorax and a crescent shapped bump on the thorax near the abdomen (I think all of the bees have one of these but it is more pronounced with the lack of hair). The abdomen is darker and shinier on the gold/amber parts and the black near the stinger is more solid instead of in several distinct bands.
There is usually a disturbance where one or two of "mine" are working over the stranger. At times I have seen one of the stranger bees carried and flown a considerable distance away from the hive (pretty impressive feat!). I first noticed them a month or so ago when it was pretty hot and dry and there were a good number of them at my hive. We got that in control by reducing the entrance and with the start of a fall flow but occasionally there are still one or two of these that show up.
I am not aware of any managed hives in the half mile or so surrounding my location but I know bees forage for much longer distances. Will they also rob in as large a radius as they forage or does robbing usually happen closer to home?