After going through the hive, and taking photos, I sent all the photos to John Babb. He and I discussed this, back and forth, via email. He is convinced that, even though it was late in the season, the colony swarmed.
All the evidence of a swarm was there: multiple swarm cells, one cell that looked like the queen emerged from the bottom of the cell, the other swarm cells torn open on the side where the first emerging queen most likely destroyed them, and an amount of dead bees consistent with what would be left after a swarm (there certainly weren’t enough dead bees to represent the entire hive – I even thought for a while that they might have actually absconded).
So the new queen either was not able to successfully mate that late in the fall, or she failed to return from her mating flight, or she got injured, or she failed in some other way.
John noted that, even though it was late in the season, we had very warm temperatures in September and October. He said:
“[Swarming] would be my thought. I looked and saw that Sept thru Oct, 2015, Salida had 53 low to 81 high. The bees would still be in the expansion & honey mode not knowing that the next month would be colder. I can see why they would swarm and it was too late to make another queen if the first new queen failed. If you had 2 hives you could have combined the queenless hive with the good hive.
Perhaps we should take a few swarm cells, incubate them and keep a queen in a NUC for an emergency? This should provide some material for conservation. Should we bank a queen or 2?
Should we inspect our hives weekly in the fall or would every 2 weeks be good to catch a late swarm?
I took photos on October 16th that show a large amount of brood in the hive. [Shown in a previous post on that date.] And, at that point, there were still quite a few drones. So, John’s comment that “the bees would still be in the expansion & honey mode” (due to the warm temperatures) seems to be corroborated by the photos I took in mid October.
After this experience, I’m determined to keep a couple of bait hives in my yard throughout the 2016 season. Doing that, I hope to not only catch any other swarms in the area but also any of my own bees that swarm.