When is there more than one queen in a hive? Or is it always “There can be only one!”?
One queen at a time is the norm. More than one queen can be seen by the beekeeper if the workers have raised a replacement queen for the existing one, usually because they sense the older queen is failing. Sometimes in the spring, mother and daughter are both in the hive and laying but later in the season, the mother has disappeared.
In a different situation, when honey bees are swarming to start a new colony, the original queen leaves before the new queens in cells emerge, unless the swarm flight is delayed by inclement weather. Sometimes after the original queen has left with half or more of the colony, the remaining workers do not allow the first new queen emerged to kill the other new queens still in their cells or as soon as they emerge. So, until each queen leaves with a smaller swarm, there is temporarily more than one queen in the hive.