I just found this fantastic photograph of a queen cup and I wanted to share it with you. These cups are built by the bees on the surface of the comb. The bees select a regular cell as a base and then enlarge it. If the queen lays an egg in one of these cups it can be expanded into a long peanut-shaped queen cell. Otherwise, it goes unattended.
The bees may build one or dozens of these throughout the hive, the number being dependent on the bees’ genetics. After a while, the bees may tear down an empty cup and use the wax elsewhere, or they may just leave it alone.
Although most queen cups remain empty, some will be used to raise supersedure queens (queens reared to replace the existing queen) or swarm cells if the colony is preparing to swarm. Supersedure cells are generally built on the face of the comb while swarm cells are usually placed along the bottom edge of the comb.