FIFTEENTH ANNUAL YEAR BOOK — PART VIII. 507 



be produced greatly increased muscular activity is required, and in Col- 

 ony C in cold weather bees in the center of the shell of insulating bees 

 were seen fanning vigorously and executing other movements, such as 

 shaking and rapid respiration. We thus have the paradoxical condition 

 that bees fan to heat the cluster in winter as well as to cool the hive in 

 summer. Observations of this kind were repeated beyond number, and 

 this theory of the method of heat production is entirely supported by the 

 repeated observation of a humming noise from the cluster during cold 

 weather. 



A few details of the observations on Colony C may be of interest. For 

 example, one bee was observed fanning vigorously for TY2 minutes (9.53 

 to 10.001/2 a. m., January 23), while the other bees kept a space cleared 

 for it. The temperature of the nearest thermometer rose %° F. during 

 this time. At 9.52 this thermometer was almost a degree cooler than at 

 the time of greatest heat during the fanning. The rapidity of fanning of 

 the wings varied, and toward the end of the time it became so slow that 

 the outline of the wings was distinguishable. After the excessive activity 

 this bee stood in the same place for a time. Rapid respiration may play a 

 more important part in heat production than at first appears. One bee 

 was observed to breathe 21 times in 14 seconds and then cease the rapid 

 respiration. On other occasions 50 or more bees would begin shaking 

 their bodies from side to side. 



THE EFFECT OF CHANGES IN EXTERNAL TEMPERATURE ON THE HEAT PRODUCTION. 



Another colony (Colony A) was used during the winter of 1912-13 to 

 determine the responses of a normal colony to changes in outer tempera- 

 ture. It also was located on the roof, where the bees were free to fly 

 when ever the weather permitted, and where it was exposed to rapid 

 changes in temperature. It was in a 10-frame Langstroth hive, the en- 

 trance being reduced to % inches deep and eight inches wide, and the 

 colony was not packed or given additional protection. In this hive we 

 placed nineteen electrical thermometers, three on the bottom board in a 

 row down the center, one in each upper corner and twelve among the 

 combs, distributed in such a way that the cluster could never get away 

 from all of them. Readings were made hourly from 9 a. m. to 4 p. m. 

 through the entire period of observation (September 26 to March 28), 

 except Sundays and holidays, and at intervals additional special series of 

 readings were made every 15 minutes (sometimes every 30 minutes) dur- 

 ing the night (5 p. m. to 8:45 a. m.) for periods of several days each. In 

 all 41,413 records were made of temperatures in Colony A. 



The reaction of the cluster in heat production, as induced by changes 

 in external temperature, is well shown by the records made from noon 

 November 13 to 2 p. m. November 15 (1912), when readings were made 

 hourly from 9 a. m. to 4 p. m. and every 15 minutes at night. From noon 

 on November 13 the outside temperature dropped slowly until 6 a. m., 

 November 15, and the weather was cloudy, so that the bees did not fly. 

 At noon on the 13th the outside temperature was about 69.2° F. and all 



