506 IOWA DEPARTMENT OF AGRICULTURE 



unusually active the adjoining bees move away, leaving an open space in 

 which it can move freely. Two bees may often be seen tugging at each 

 other. In addition to the bees between the combs, placed as above de- 

 scribed, others are in empty cells of the comb on which the cluster is 

 always formed, always with their heads in. A verification of these state- 

 ments is contained in the following observations, and the experiment may 

 easily repeated by anyone: For the purpose of obtaining a colony with- 

 out combs for another experiment, a hive was opened December 15, 1913, 

 while the outside temperature was low enough to cause the formation of 

 a compact cluster. When the combs were separated the circle of bees in 

 the shell was clearly observed. When a comb from the center of the clus- 

 ter was shaken the active bees in the center of the circle dropped off 

 readily, and those in the outer shell which were somewhat sluggish were 

 removed with more difficulty. After this was done those occupying empty 

 cells in the center of the sphere backed out of the cells and were shaken 

 off. Finally those occupying cells in the border of the sphere backed out, 

 showing a well-marked circle on the combs. Evidently the bees in the 

 shell, whether in the cells or between the combs, are less active than 

 those in the interior of the cluster. Naturally such a manipulation as 

 this is not to be recommended, except for purposes of demonstration. 



It is clear from observations previously recorded that the highest tem- 

 peratures are those of points in the center of this shell, and this is to be 

 expected, as the heat is generated here. The outer shell constitutes an 

 ideal insulator for the conservation of the heat, since the bees arranged 

 so close together form small dead air spaces in their interlacing hairs, 

 especially those of the thorax, and afford still more insulation with their 

 bodies. The abdomens of the bees in the outer row are practically sep- 

 arate one from another, and must often be exposed to severe cold. That 

 this method of conserving heat is effective is shown by observations on 

 undisturbed colonies out of doors. For example, on January 14, 1914, there 

 was at 9 a. m. a difference of 68° F. between thermometers 14 (center of 

 the sphere) and 16 (outside the cluster) of Colony D, which were less 

 than 41/2 inches apart on the same level in the same space between combs, 

 and a difference of 75° F. between this couple and the bottom board 4i/i 

 inches below it. What this difference might sometimes be in colder cli- 

 mates may be imagined. Examples of this kind might be multiplied indefi- 

 nitely from the records of these experiments. 



The source of the heat of the cluster must, of course, be the oxidation of 

 the food consumed by the bees. The bee is classed as a cold-blooded ani- 

 mal, in that the temperature of the individual bee is practically that of 

 the surrounding medium. There is obviously, from the records just given, 

 no internal regulation of the temperature of the body, such as is found in 

 birds and mammals, for the temperature of a broodless cluster varies 

 greatly. From the observations made on the various colonies, especially 

 Colony C, it is clear that heat for the warming of the cluster is produced 

 by muscular activity. While, of course, some heat is doubtless liberated 

 by other life processes, this is practically negligible when bees are 

 quiet, as in Colony A, when above 57° F. That higher temperatures may 



