508 IOWA DEPARTMENT OF AGRICULTURE 



the points within the hive were 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 mean- 

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

 the temperature wthin 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 move- 

 ment 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 ther- 

 mometers 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 tem- 

 perature begins to rise, the cluster temperatures drop slowly to meet the 

 outside temperature. The generation of heat is reduced, or even discon- 

 tinued, 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 tempera- 

 ture is above about 69° F. that it is less constant than when it is below 

 this temperature, indicating that 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 observations 

 tend to confirm what was first seen on the record presented here, we feel 

 justified in presenting a definite statement 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 bee« 

 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 the lower critical temperature, which is for the present stated as 57° F., 

 the bees begin to form a compact cluster, and if the temperature of the 

 air surrounding them continues to drop they begin to generate heat 

 within the cluster, often reaching temperatures considerably higher than 

 those at which they were formerly quiet and satisfied. It is evident. 



