ung virgin queen has a limited time to mate. If she is unable to fly for several days because of bad weather and remains unmated, she will become a "drone layer." Drone-laying queens usually signal the death of the colony, because the workers have no fertilized (female) larvae from which to raise worker bees or a replacement queen. Supersedure may be forced by a beekeeper, for example by clipping off one of the queen's middle or posterior legs. This makes her unable to properly place her eggs at the bottom of the brood cell; the workers detect this and then rear replacement queens. When a new queen becomes available, the workers kill the reigning queen by "balling" her, clustering tightly around her. Death through balling is accomplished by surrounding the queen and raising her body temperature, causing her to overheat and die. Balling is often a problem for beekeepers attempting to introduce a replacement queen. If a queen suddenly dies, the workers will attempt to create an "emergency queen" by selecting several brood cells where a larva has just emerged which are then flooded with royal jelly. The worker bees then build larger queen cells over the normal-sized worker cells which protrude vertically from the face of the brood comb. Emergency queens are usu