In modern removable frame hives the nursery area is in the
brood chamber, which beekeepers prefer to be in the bottom box. In the late winter and early spring as the brood cycle begins, the queen starts to lay eggs within the
winter cluster in proximity to available honey stores. Honey bees tend to greatly expand the brood chamber as the season progresses. The relative location of the brood chamber within the beehive may also change as bee keepers add more boxes or as wild bees build fresh comb into available cavities. Some beekeepers ensure that the
queen will not go into the upper boxes (called
supers or
honey supers) by placing a screen called a
queen excluder between the boxes. The screen has precisely measured open spaces through which a
worker bee can pass, but not a queen. Some beekeepers do not use excluders, but try to keep the queen within the intended brood area by keeping a honey barrier of capped honey, which the queen is reluctant to cross, above the brood. In feral hives the honey bees tend to put the brood at bottom center of the cavity, and honey to the sides and above the brood, so beekeepers are trying to follow the natural tendency of the bees. In the mid to late spring, just before a bee hive would naturally split by
swarming,
beekeepers often remove frames of brood, with adhering bees, to make up new starter hives, called "nucs" or
nucleus colonies. In areas where the
climate is mild, one frame may be sufficient to start a new colony, with an added queen. But usually two to three frames are used, together with a frame that is predominantly honey. This ensures that there will be enough adult bees to provide the brood the adequate temperature and sufficient feed if there are a few rainy days when bees cannot gather nectar. If there are not enough adult bees to warm the combs, the brood may die from cold temperature overnight (aptly called "chilled brood"). ==Brood development==