-—What was it?-—
It was reproduction. A colony of bees was reproducing.
The way it is done is the original colony grows to the point it is prosperous and numerous. A decision is made and it then sets about developing a new queen. A special cell or cells is prepared and eggs are transferred and then given extreme care. The slightly larger cell and the very special care produces a new queen from an ordinary egg.
At some auspicious point, the old queen and those chosen or designated leave and fly off to establish a new colony. The time is determined by the maximum or near max spring bloom and lots of pollen and nectar. The new colony requires wax and sustenance.
At some point in anticipation of the move, scouts have been on the look out for the new digs. Typically there will not be agreement on where. So, the queen finds a convenient place to light and all the bees form a large mass on the tree branch or other place where she is. A decision will then be made as to where to go or which of the locations is most acceptable. The decision might be quick or it might take several days. Politics you know it’s hart to get agreement out of 30,000 bees. The whole swarm will then follow the queen into the new quarters and set about building a new home. It is after all a sexual thing and they are not as aggressive as they are guarding their established home.
My take was that your house was selected as the new home and then rejected and the swarm left to what was determined to be a better place. It is also possible and even likely that the queen selected your house as the swarm resting place while the decision was being made to move to.
As a beekeeper, I printed up a notice every spring and posted it at the volunteer fire department. “Call Bert if you need a swarm removed.” I captured many new swarms this way. You spray the mass heavily with sugar water and they become very docile. You can then brush them into a card board box for transport. At home,you then dump them all into a prepared hive. They immediately recognize their good fortune and go to work setting up house keeping.
Meanwhile back at the old colony when a new queen emerges, she quickly searches or possibly is directed to any other queen cells. She stings the other potential queens, killing them off. At some point she leaves and flies high followed by drones. One or several drones mates with her on this flight. She then returns and begins the never ending task of laying eggs.
Thus, the cycle of reproduction is complete. An individual, a new queen was produced and as a result a new colony was reproduced.
I kinda suspected. I had never captured a wild swarm and had a call in to a beekeeper friend who knows much more about such things. Looks like I missed a great opportunity.