What signals are these ants detecting? It sure looks like they hear, smell, or feel something... something big!
citronella ants are subterranean farmers... farming aphids and mealybugs down there in their hidden world. Here is a photo of a tiny yellow ant sipping a droplet of honeydew from one of its "cows".
Whatever triggers the swarming of these yellow ants, it's a yearly thing for them to send off their winged ants to start other new ant colonies.
Notice that some kind of communication is happening among all those ants.
Incidentally, these boys aren't sluggards, but there is still wisdom to be had by considering the ways of the ant. In the context of this event, I suppose one thing they could learn is... that there is a right time to leave home and start a new one (I might add "Hopefully, not far away").
BTW, this "flight of the queens" took place in the same sand volleyball court where I took some pictures of ground-nesting solitary wasps with their nests and prey.