Queen Excluder
Lexikon
The queen excluder is a grid made of metal or plastic that is placed between the brood chamber and the honey super.
The queen excluder is a grid made of metal or plastic that is placed between the brood chamber and the honey super. Its slots are sized so that the comparatively slender worker bees can crawl through unhindered and carry nectar upward, while the much larger queen and the broader drones cannot fit through. This keeps the brood confined to the brood chamber. The excluder is not a mandatory part of a hive but a tool: there are management styles with a queen excluder and without one.
The practical benefit is that the honeycombs stay free of brood. This considerably simplifies the harvest, since full honeycombs containing areas of brood must not be extracted. Anyone working without a queen excluder must therefore check every single comb for this when harvesting. A second advantage only shows up later in the year: comb that has never held brood is markedly less vulnerable to wax moths and stores without any trouble.
Two typical mistakes happen when fitting the excluder. First, some beekeepers put the grid on without being sure where the queen currently is. If she is above it, she gets shut into the honey super and keeps laying there. So look for the queen before fitting the excluder, or otherwise make sure she is below it. Second, drones that are still in the honey super when the excluder is fitted can no longer get out of the hive.
A queen excluder is no substitute for space. If the bees do not take to the honey super, this is often because the colony is still too weak for the expansion. The LWG names as countermeasures temporarily removing the queen excluder and moving full combs from the brood chamber up into the super, so the bees accept the new space. If a further honey super is placed directly on top of the brood chamber, it needs either the excluder or enough free space in the brood chamber, otherwise the bees will end up brooding in the honeycombs against the beekeeper's wishes.