THE BEE-KEEPERS' REVIEW 



24; 



be seen from the accompanying 

 (fig. 1) that at noon on the 13th 

 the outside temperature was about 

 69.2° F. and all 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 with- 

 in the cluster, which had in the 

 meantime become warmer. From 

 this time until 6 p. m. the next 

 day ( 14thj the temperature with- 

 in the cluster gradually dropped 

 as the cuter air cooled, until the 

 lowest one (No. 9) was 5 7° 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 de- 

 finite 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 inci- 

 dental to the formation of a com- 

 pact cluster, and from this time un- 

 til the next day at the close of the 

 series of readings the thermome- 

 ters within the cluster showed a 

 considerably higher temperature 

 than the outer air, or than the 

 thermcmeters 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 tem- 

 perature was reached and the outer 

 air began to get warmer (6:15 a. 

 m., November 15), there was a ten- 

 dency 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 gen- 

 eral after a period of cold, when 

 the outside temperature begins to 

 rise, the cluster temperatures drop 

 slowly to meet the outside temper- 

 ature. 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 great- 

 er activity, as in flight. It is found 

 also by taking more frequent read- 

 ings when the cluster temperature 



is above about 69° F. that it is 

 less constant than when it is be- 

 low this temperature, indicating 

 that at temperatures above this 

 point the bets move about to some 

 extent, while between 57° tnd 69° 

 they are quiet, unless flight is 

 desirable owing to a long confine- 

 ment. 



This series of readings is sup- 

 ported by numerous records taken 

 on this and other colonies through- 

 out the winter and, since all the 

 observations tend to confirm what 

 was first seen on the record pre- 

 sented here, the authors feel just- 

 ified 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 investi- 

 gators fails to show a similar 

 statement on this subject. When a 

 colony is without brood, if the 

 bees do not fly and are not dis- 

 turbed and if the temperature does 

 not go too high, the bees generate 

 practically no heat until the cool- 

 est point among the bees reaches 

 a temperature of about 57° F. At 

 temperatures above 57° F. a com- 

 pact cluster is not formed, but the 

 bees are widely distributed over 

 the combs. At the lower critical 

 temperature, which is for the pres- 

 ent stated as 57° F., the bees be- 

 gin to form a compact cluster, and 

 if the temperature of the air sur- 

 rounding them continues to drop 

 they begin to generate heat v>ithin 

 the cluster, often reaching temper- 

 atures considerably higher than 

 those at which they were former- 

 ly quiet and satisfied. It is evident 

 therefore, that the temperature 

 within the cluster is far from be- 

 ing uniform in winter, as has been, 

 in a sense, assumed among practi- 

 cal beekeepers At the temperature 

 at which other insects become less 

 active (begin hibernation) the 

 honeybee becomes more active and 

 generates heat, in some cases until 

 the temperature within the cluster 

 is as high as that of the brood nest 

 in summer. To sum up, when the 

 temperature cf a colony of undis- 

 turbed broodless bees is above 57° 

 P. and below about 69° F. the bees 

 are quiet and their temperature 

 drifts with the outer temperature; 

 at lower temperatures they form 

 a compact cluster, and the temper- 

 ature within it is raised by heat 



