A proper beekeeper will answer better than me, but if they are visibly all feeding then I think you have just got a lot of bees. A swarm hangs together in a pulsating mass, very difficult to distinguish individuals except the dozen or so joining or leaving. We had one in July, about the size of a rugby ball, a local keeper came and collected the swarm by knocking the mass off into a box. Fascinating but rather creepy.