A colony of bees consists of three castes of bee:
a queen bee, which is normally the only breeding female in the colony;
a large number of female worker bees, typically 30,000–50,000 in number;
a number of male drones, ranging from thousands in a strong hive in spring to very few during dearth or cold season.
Drones are the largest bees in the hive (except for the queen), at almost twice the size of a worker bee. Note in the picture that they have much larger eyes than the workers have, presumably to better locate the queen during the mating flight. They do not work, do not forage for pollen or nectar, are unable to sting, and have no other known function than to mate with new queens and fertilize them on their mating flights. A bee colony generally starts to raise drones a few weeks before building queen cells so they can supersede a failing queen or prepare for swarming. When queen-raising for the season is over, bees in colder climates drive drones out of the hive to die, biting and tearing their legs and wings.
YouTube | Bees in the garden - Catching a swarm of bees at Casa Vacanze Podere Santa Pia