TEMPERATURE OF THE HONEYBEE CLUSTER IN WINTER. 5 



then cooler than the outside air, due to the fact that it took some 

 time for the inside of the hive to warm up. At 4 p. m. the outside 

 temperature had dropped to 65.3° F., when it was lower than any 

 of the points within the cluster, which had in the meantime become 

 warmer. From this time until 6 p. m. the next day (14th) the tem- 

 perature within the cluster gradually dropped as the outer air cooled, 

 until the lowest one (No. 9) was 57° F. (Outside temperature, 

 48.2° F.) The generation of heat began at 6.15 p. m. at this point, 

 which was to one side of the cluster, and is to be attributed to the 

 movement of the bees in forming a definite cluster. At 6.30 p. m. 

 a rise in temperature was noticed on thermometer 19, at the other 

 side of the cluster. Until 10,15 p. m. the changes in temperature 

 are probably to be interpreted as incidental to the formation of a 

 compact cluster, and from this time until the next day at the close 

 of the series of readings the thermometers within the cluster showed 

 a considerably higher temperature than the outer air, or than the 

 thermometers outside the cluster. The maximum in this series 

 was reached at 3.15 a. m., November 15, when thermometer 12 in 

 the center of the cluster registered over 89.4° F. 



After the coldest outside temperature was reached and the outer 

 air began to get warmer (6.15 a. m., November 15), there was a 

 tendency for the cluster temperatures to drop. This is somewhat 

 noticeable in the case now being discussed, and is more clearly seen 

 in records obtained in other series. In general, after a period of 

 cold, when the outside temperature begins to rise, the cluster temper- 

 atures drop slowly to meet the outside temperature. The generation 

 of heat is reduced, or even discontinued, only to be increased when 

 the outside temperature again drops, or when it gets high enough to 

 induce greater activity, as in flight. It is found also by taking more 

 frequent readings when the cluster temperature is above about 69° F. 

 that it is less constant than when it is below this temperature, indi- 

 cating that at temperatures above this point the bees move about to 

 some extent, while between 57° and 69° they are quiet, unless flight is 

 desirable owing to a long confinement. 



This series of readings is supported by numerous records taken on 

 this and other colonies throughout the winter and, since all the ob- 

 servations tend to confirm what was first seen on the record pre- 

 sented here, the authors feel justified in presenting a definite state- 

 ment of the reactions of the cluster to outside temperatures. It may 

 be added that a careful study of the records of previous investigators 

 fails to show a similar statement on this subject. When a colony is 

 without brood, if the bees do not fly and are not disturbed and if the 

 temperature does not go too high, the bees generate practically no 

 heat until the coolest point among the bees reaches a temperature of 

 about 57° F. At temperatures above 57° F. a compact cluster is 

 not formed, but the bees are widely distributed over the combs. At 



