10 BULLETIN" 96, U. S. DEPARTMENT OF AGRICULTURE. 



failed to demonstrate it at the time. This same point is illustrated 

 by the figures presented in figure 6. Such conditions suggest the 

 complications which arise in attempting to correlate the colony tem- 

 perature with the consumption of honey. 



GENERAL PHENOMENA OF THE CLUSTER IN WINTER. 



During the winter the bees are relatively quiet; the cluster expands 

 and the bees fly only in the warmth of the warmest days. The heat 

 maintained in the cluster has a general relation to the prevailing 

 temperature of the air. 



This relation of the cluster temperature to air temperature is 

 especially evident in a comparison of the maximum and minimum 

 temperatures of the several thermometers of the hive with the tem- 

 perature at the outside thermometer, o. The daily maxima and 

 minima were practically synchronous for all of the thermometers 

 with the exception of c, which usually had its maximum when the 

 temperatures registered by the other thermometers were lowest. 

 Conversely, the minimum of c occurred when the outside thermometer 

 and the others in t]ie hive were at their highest points. This will be 

 explained in detail under a following caption. With the exception 

 of c, then, and for the particular conditions under which this colony 

 was kept, the minima occurred daily some time between 6 a. m. and 

 12 m., but usually about 8 or 9 o'clock. The maxima occurred daily 

 in the afternoon, usually between 2 and 4 o'clock. 



While c registered the highest in cold periods, the temperature 

 recorded by the other thermometers showed a similarity with the 

 prevailing temperature of the air. Thus, in periods of cold, as for 

 example in December, the thermometers in the hive as a whole 

 registered lower than they did in warm periods. In warm periods, 

 when the bees are able to expand the cluster and move about, the 

 maximum cluster temperature lacked but a few degrees of the 

 maximum summer temperature. This is repeatedly shown in 

 figure 7 ; and in March, on a warm day, the temperature reached the 

 extreme of 33.2° C. (91.76° F.). The temperature of the cluster did 

 not fall below 17° C. (62.6° F.), and usually the bees did not permit 

 the temperature of the cluster to fall below 20° C. (68° F.). 



The amplitude of the fluctuations between the maximum and 

 minimum temperatures showed a close relationship to the external 

 conditions. In the center of the cluster, for instance, c registered 

 much more constantly than the thermometers in the outside layer of 

 the cluster. The daily oscillations of c were usually not greater than 

 1 to 5 or 6 degrees Centigrade. On the contrary, in the case of the 

 other thermometers in the hive which were more affected by the rise 

 and fall of the temperature out of doors, the amplitude of the oscilla- 

 tions was as great as 3 to 20 degrees Centigrade. The center of the 

 cluster, therefore, shows more clearly the activities of the bees. The 



