FIFTEENTH ANNUAL YEAR BOOK— PART VIII. 505 



THE SOURCE OF HEAT IN THE COLONY. 



It is a well-known fact that bees generate heat during cold weather, so 

 that the temperature of the cluster never drops very low. The lowest 

 temperature that we have found is 57° F. In order to see what the bees 

 do during this period of heat production, we devised a special outfit so 

 that we could see the inside of the cluster. A colony in winter forms a 

 compact, approximately spherical cluster and on the outside of the cluster 

 there is nothing that one can see that suggests the heavy heat production 

 that must take place. However, a narrow hive was provided, with double 

 glass sides and top, with an air space between the sheets of glass to act 

 as an insulation. The stores were then so arranged that the only place 

 available for the cluster was next to the glass on one side. In the outside 

 space were placed a number of the electrical thermometers which we used 

 and which are briefly described in Bulletin No. 93 of the Department of 

 Agriculture, to which those interested are referred. In the space pro- 

 vided there was not room for a spherical cluster, so the bees formed a 

 hemisphere, the equator of which was against the glass. This showed as 

 a circle of bees on the glass, exposing to view the center of the cluster. 



It was then clearly demonstrated that the cluster is not uniformly com- 

 pact. The cluster consists, between the combs and sometimes above and 

 below them, of an outer shell of bees packed close together, with their 

 heads toward the center. The thickness of this ring varies with the 

 weather being thicker when the outer temperature is warm and when 

 less heat production is needed, and becoming thinner with the increase in 

 heat production. This is because when more heat is produced more beees 

 are needed for this work, leaving less for the outer rim. 



In order to expose this colony (Colony C) to rapid changes in tempera- 

 ture, the hive was placed on the roof of the building, and while one per- 

 son watched the bees another read the temperatures in the room below 

 where the instruments were located. A telephone was installed, so that 

 the two persons could be in constant communication, head pieces being 

 used, so that the hands of both observers were free. The observations 

 made on the roof were then given over the telephone and all records were 

 made below. This colony was of course in the light, but the normal clus- 

 ter was nevertheless observed. The colony was disturbed as little as pos- 

 sible during the observations to eliminate abnormal conditions. 



The nearly spherical cluster of bees consists, between the combs and 

 sometimes above or below them, of an outer shell of bees close together, 

 with their heads toward the center. This ring may be several layers thick. 

 The position with the heads inward is typical, except when condensed 

 moisture drops on the cluster, as it often does in cool weather, when the 

 bees at the top turn so that their heads are upward. The bees in this 

 outer shell are quiet, except for an occasional shifting of position. Inside 

 this rather definite shell the bees between the combs are not so close 

 together, nor are they headed in any one way. Considerable movement, 

 such as walking, moving the abdomen from side to side, and rapid faa^ 

 ning of the wings, takes place inside the sphere, and when a bee becomes 



