Marking a queen bee for identification - GIF

[Frank S]

Must have a keen eye to spot a queen bee in that roiling mass. I couldn't see much difference.

Just look for a bee with shorter wings longer abdomen and longer legs and you will have the queen, if a queen gets too old or happens to die in a healthy hive the workers can feed a larva with honey that has extra nutrition in it, I think it is called royal honey when the new queen is formed, she gets special treatment until maturity.
Not all hives are successful in re-queening their hive, So the beekeeper has several methods to ensure a new queen can hatch. I'm not a beekeeper but I know a few who often split hives nad help the bees to create new queens beofore splitting the hives.