Though I had read that bees will sometimes "beard" on the outside of their hive in hot weather, I'd never seen it in person.
But it was well into the 90s in L.A. today, and when I got home (after 6pm), I found that our super-achiever hive was in full-on bearding mode.
I hope this doesn't mean they're getting ready to swarm. They still have lots of room in the top box, and we even removed a couple of frames of brood over the last few weeks. We shall see.
UPDATE (the next day):
On Kirk's advice, we opened up more room in the hive by moving some honey frames upwards and adding a fourth box. There's plenty of brood, so it looks like the queen is happily working away.
This afternoon there was far less bearding, despite the day being hotter. Thanks, Kirk!