52 



FIFTEENTH ANNUAL REPORT OF THE 



Dr. E. F. Phillips, in. charge Bee Culture Investigations, Washington, D. C. 



distinct fail into these two classes, ex- 

 cept for some that are usually given 

 which the authors do not believe to be 

 operative. 



Excessive Heat-Generation. 



At hive temperatures between about 

 57° and 69° F., a normal broodless 

 colony of bees does not form a cluster, 

 but the bees remain inactive on the 

 combs. When the temperature of the 

 air immediately surrounding the bees 

 (not the temperature of the air outside 

 the hive) falls to 57° F., or lower, they 

 form a cluster and those in the center 

 begin to generate heat by muscular ac- 

 tivity, while those in the outer portion 

 serve as insulators by crowding elose 

 together, usually with their heads 

 toward the center of the cluster. The 

 innermost portion, rapidly acquires a 

 temperature considerably higher than 

 that of the air about the bees before 

 clustering was necessary, often going 

 to 90° F. in normal colonies and higher 



in abnormal ones. The number of bees 

 engaged in heat production increases 

 as the outer temperature falls and the 

 insulating zone is consequently de- 

 creased in thickness but becomes more 

 compact. The entire cluster becomes 

 smaller as the outer temperature falls. 

 If bees can be kept in an environment 

 such that the temperature of the air 

 irnmediately surrounding them is 57° 

 F. or- slightly above, they are saved 

 mvch unnecessary and unprofitable 

 labor. To the theoretical objection 

 that bees need exercise, it is necessary 

 only to state that the authors have so 

 wintered bees in a cellar aS" well as out- 

 doors with wonderfully successful re- 

 sults. If bees are kept in a cellar under 

 the best conditions the results are ex- 

 cellent, but it~is,not proposed to dis- 

 cuss this more complicated phase of 

 the subject here. If wintered outside 

 in a packing case with abundant insu- 

 lation, any heat generated escapes 

 slowly and the temperature of the air 



