When a bee colony loses a queen -- say, she's accidentally killed -- the worker bees notice the absence of a chemical she produces called a "pheromone." In response to the absence of the queen's scent, the workers begin a process of "emergency queen rearing." They start building queen-size rearing chambers for about ten to twenty young female larvae. The process of royal succession is similar if the queen is dying of old age. As she ages, the queen produces less pheromones. The decline in pheromone concentration signals the workers to start building queen-size cells. The queen herself lays the eggs of her potential successors into these cells. Ordinarily, these eggs would hatch into female larvae who would grow up as workers. But since they're inside special larger, vertically-oriented cells, the workers know to feed these princesses a special food called "royal jelly." This diet creates a fertile queen rather than a sterile worker. The first queen to emerge from her cell as an adult will sting the other developing queens to death in their cells before they hatch. If two should emerge at the same time, then the rival queens will have a battle to the death.

If no eggs or larva are available to be raised as queens, the total absence of pheromones will cause some of the workers (all are female) to lay eggs. Since the workers never mated, all they can lay is male (drone) eggs. All the drones can do is mate; they do no work, so the hive will still die as the workers die off. But the drones at least have a chance of mating with other queens from other hives to continue the hive's genes, even though the drone's home hive is doomed. If this is a beekeeper's hive, sometimes the hive can be re-queened by the keeper with a new queen from elsewhere. But it's a tricky process, and does not happen in nature.