@dlowan,
Actually, queens aren't much bigger than wor ker bees....are you sure it wasn't a wasp or a hornet?
Swarms are different from mating flights.
Swarms happen when a hive divides and part of it goes to establish a new hive with a young queen.
And sorry, when I first posted I thought you asked about ants for some reason. Mated queen bees go somewhere they think will be a good spot, not underground.