[Illustration: Fig. 1.--Map of the United States showing regions where cellar wintering is practicable, based on the average temperature of January. From data furnished by the United States Weather Bureau.]
The placing of bees in a cellar is only another way of putting insulation about the hives, the only difference being that in the cellar all of the hives are protected alike and the protection is placed about the apiary instead of around hives in groups or singly. It follows that the principles which apply to successful outdoor wintering apply equally to the protection of the bees in the cellar. It is urged, therefore, that before attempting to winter bees in the cellar, the beekeeper study the bulletins[1] of the department in which these principles are set forth.
[1] Department Bulletin 93, The Temperature of the Honeybee Cluster In Winter. Farmers' Bulletin 695, Outdoor Wintering of Bees.
Before deciding whether or not the bees are to be wintered in a cellar, several factors should be considered, the chief of these being (1) the winter climate, (2) the kind of winter stores, and (3) the location of the apiary as regards wind protection.
In any locality where the average temperature of the winter months falls below 25° F. (zone 1) cellar wintering may be practiced with profit, and in localities where the average temperature of these months falls as low as 15° F. (zone 2) cellar wintering is much to be preferred. Figure 1 shows the boundaries of these zones for the United States for the month of January, which may be taken as typical of the winter months. It will be noted that these zones do not follow parallels of latitude. As was pointed out in the bulletin of the department on outdoor wintering,[2] it is quite possible to protect bees in zone 1 sufficiently to winter them outdoors, but if a proper cellar is provided, if conditions within the cellar are correct, and if the stores are good and the colonies are strong, just as good results may be obtained from cellar wintering.
[2] Farmers' Bulletin 1012, Preparation of Bees for Outdoor Wintering.
In zone 1 the average temperature of the outside air during the mouth of January is 25° F., or lower in the more northern parts of the zone. This means that in colonies wintered outdoors the bees are compelled to overcome this degree of cold at all times during the coldest part of the winter. If they are so well packed that the heat which they generate is lost slowly, they are able to generate sufficient heat to make the interior of the hive warm enough to allow them to break their cluster as is necessary. In zone 2, however, the bees will be compelled to generate heat sufficient to overcome the more severe cold of that zone, and this calls for the expenditure by the bees of so much more food and vitality that it is more economical to put them in a good cellar during the months of the most severe cold, and cellar wintering is therefore preferable.