At first I thought termites, but then I wondered why they were congregating with so many ants. Thank heavens for the internet. I found that they're flying ants and their swarming is a common summertime occurrence. Spraying is out of the question - not with a bird nest full of babies on the deck. Update, a few hours later: They're all gone, very thankfully! I did nothing but put out a couple of ant baits...I think they just are off looking to establish new colonies. Those with wings are potential queens.