Throughout the year, I've seen evidence of my hive having swarmed - namely queen cells which are hatched, and new queens which are unmarked. Each time I haven't seen any physical evidence of a swarm, e.g. when they are actually leaving the hive. At the Mass Bee field day one of the instructors said it's easy to miss the actual swarming event, as it can occur in a 5 minute timeframe.
This afternoon my wife called me at work, and mentioned she was outside and was looking up at a low flying helicopter. She just happened to notice a dark mass in the leaves of the tree waaaay up high, and sure enough, it was a swarm of bees! They were in a tree directly over where my hives sit.
Here are some pictures she took - some with the telephoto lens.
Just my luck, it was about 70 feet up in the air - too high to capture. I got home around 6:30 and expected the swarm to be gone, but it was still there.
She wasn't sure which hive threw the swarm - she seemed to notice one of the nucs (the Blue Nuc) having a lot of activity. So I suited up and took a look at that nuc. I pulled out the first frame, and there was the (marked) queen bee. So no, that hive didn't swarm. Besides, I didn't see any swarm/queen cells.
The only hives that I knew about having queen cells were the Brown Nuc and the Pink Hive. I opened up the Brown Nuc and saw that one of the queen cells had hatched - it had a nice opening where the queen had chewed open her own cell. There were a couple more cells unhatched also. But 1) I don't think the hive would swarm with a new queen right after hatching (since 2 days ago I saw the same queen cell capped), and 2) I don't think it's possible for a freshly hatched queen to fly right away. I thought they need to "harden" a little first. I'm not sure - I'll ask on the bee forums.
It could be that another of my hives had developed swarm cells - I wasn't necessarily 100% diligent in looking for them the last time I inspected. Anyway, I didn't feel like diving into the big hives tonight. I'll do some looking around the next time I do a big inspection.
Anyway, I have a nuc sitting on my chimney as a swarm trap. And since the swarm was still in the tree tonight, I set up a new empty hive on a table on my desk, with some old frames, and put a little lemongrass oil as a scent inducer. I've heard that swarms don't like to re-hive in/near their own bee yard, but it's worth a chance.
I'll update if the hive decides to take up residence in my equipment. It'd be a first!