ILLINOIS STATE BEE-KEEPERS' ASSOCIATION 



71 



(Outside temperature, 48.20F.) 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 ther- 

 mometer 19, at the other gide of the 

 cluster. Until 10.15 p. m. the changes 

 in temperature are probably to be in- 

 terpreted 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 consider- 

 ably 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., No- 

 vember 15th, when thermometer 12 in 

 the center of the cluster registered over 

 S9.4op. 



After the coMest outside temperature 

 was reached and the outer air began 

 to get warmer (6.15 a. m., November 

 15), there was a tendency for the clus- 

 ter 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 temperatures 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, indicating that at tem- 

 peratures above this point the bees 

 move about to some extent, while be- 

 tween 57° and 69° they are quiet, un- 

 less 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 previ- 

 ous investigators fails to show a simi- 

 lar 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 

 570F. At temperatures above oTop. a 

 compact cluster is not formed, but the 

 bees are widely distributed over the 

 combs. At the lower critical tempera- 

 ture, which is for the present stated as 

 57 °F., the bees begin to form a com- 

 pact cluster, and if the temperature 

 of the air surrounding them continues 

 to drop they begin to generate heat 

 within the cluster, often reaching tem- 

 peratures considerably higher than 

 those at which they were formerly 

 quiet and satisfied. It is evident, 

 therefore, that the temperature within 

 the cluster is far from being uniform 

 in winter, as has been, in a sense, as- 

 sumed among bractical bee-keepers. 

 At the temperature at which other in- 

 sects become less active (begin hiber- 

 nation) 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, wtien 

 the temperature of a colony of undis- 

 turbed broodless bees is above 57°F. 

 and below 69 °F. the bees are quiet and 

 their temperature drifts with the outer 

 temperature; at lower temperatures 

 they form a compact cluster, and the 

 temperature within it is raised by heat 

 generated by the bees. 



We desire to state that while the 

 lower critical point, 57°F., appears 

 rather well established, the observa- 

 tions up to the present do not justify 

 too definite a statement concerning the 

 upper limit of. quiescence. It must be 

 emphasized that these conditions do 

 not apply when the colony has brood. 

 The rearing of brood in winter causes 

 a marked increase in heat production 

 and constitutes a condition which may 

 become one of the most disastrous that 

 can befall a confined colony. 



When the heat production of the 

 colony is explained, we are able to 

 understand to some extent the diver- 

 gence in the records obtained by other 

 observers. It has, of course, long been 

 known that bees generate heat, and it 

 has been pointed out that during cold 

 weather the temperature of the cluster 

 is often higher than during warmer 

 weather. While the temperatures 

 previously recorded are in most cases 



