90 
Beekeeping 
temperature is about 60° F., the bees do not cluster com¬ 
pactly and do not fly from the hive, even on bright days, 
but remain inactive on the combs. In this condition they 
are less active than at any other time in the cycle of the 
colony and approach most nearly to a condition of hiberna¬ 
tion. During the warmer days there is no need of a tight 
cluster, for the function of the cluster is the conservation of 
the heat generated within. When the temperature is suffi¬ 
ciently high the bees generate no heat but, whenever the 
temperature of the air immediately surrounding the bees 
drops below 57° F. (the lowest temperature which normal 
bees ever experience in the hive), they form a definite cluster. 
As the outside temperature continues to fall, the cluster 
becomes more and more compact and the temperature of 
the inside of the cluster increases rapidly. After the genera¬ 
tion of heat is begun, the temperature within the cluster 
soon reaches a point higher than that reached before heat 
generation was necessary. Within certain limits, the tem¬ 
perature of the cluster increases as the outside temperature 
drops and, as the outer temperature again rises, heat gen¬ 
eration is reduced or discontinued while the temperature of 
the cluster drifts to meet the rising outside temperature. 
Heat generation is renewed if the outer temperature again 
drops, even though the temperature of the cluster and that 
of the outer air have not yet been equalized. This pro¬ 
duces a peculiar inverse relationship between the outer 
and cluster temperatures. It is of particular practical 
importance that, within certain definite limits, the bees are 
not compelled to produce heat. 
Conservation of heat. 
The cluster consists of a hollow sphere of bees several 
layers thick, those between the combs with their thoraces 
in contact and abdomens extending outward. The cells 
within the cluster are also filled with bees. The hair on 
the thorax assists in making this living shell an excellent 
non-conductor of heat, so effective in fact that a point in- 
