Instructions
Examine the ants' bodies. Any ants with wings will probably be males or new queens. They are highly unlikely to be either workers or the queen of the colony.
Look at the comparative size of the ants. The queen is usually much bigger than the workers, sometimes several times their size.
Watch the ants' behavior. Soldier ants, while often big, take an active role outside the nest. The queen remains inside, where she is protected and is unlikely to move much, if at all, unless disturbed. The worker ants bring food to her while she continues laying eggs.