There has been considerable discussion among beekeepers as to the value
of placing packing material below the bottom boards of the hives. This
is usually provided by placing the hives on 2 by 4 inch supports or on
racks of 4-inch material. Those who have opposed this have pointed out
that "heat rises," overlooking the fact that while warm air attempts
to rise, if this is impossible other avenues of escape of warm-air
currents may be set up. Furthermore, and more important, they have
overlooked the important fact that heat escapes from the hive not only
by convection currents but by conduction and radiation as well. In an
extensive series of experiments performed by the writers it was found
that in hives packed at the top and sides most of the heat escapes
through the bottom boards; in fact, this was so noticeable that the
packing at the top and sides never served its full purpose so long as
heat was escaping rapidly at the bottoms. It may be stated, therefore,
that so long as the bottoms are unprotected there is little insulating
value in materials piled on the top and sides beyond about 2 inches.
This amount is insufficient for most parts of the United States,
therefore bottom packing should be considered as absolutely essential
wherever bees are packed.
To get the value of bottom packing it is absolutely essential that the
entrance be reduced, but it need not be closed. In a long series of
temperature readings on hives packed for several winters, the authors
were able to keep a temperature of 50° F. on the bottom boards of
packed hives directly behind the entrance openings. Those who have
condemned bottom packing have labored under the mistaken notion that it
is impossible to prevent currents of cold air through the entrance.
This is entirely possible if the entrances are adequately reduced. The
conclusion to be drawn from the experiments performed is that unless
the bottoms of hives are well packed, the beekeeper ought not to
imagine that he has packed his hives at all well.
[Illustration: Fig. 2.--The winter packing cases used in the Bureau
of Entomology apiary: _a_, Detail of tunnel to hives. In the
specifications given in this Bulletin (p. 9) provision is made for room
for a third hive body to be added in the spring.]