6 BULLETIN 93, U. S. DEPARTMENT OF AGRICULTURE. 



the lower critical temperature, -which is for the present stated as 

 57° F., the bees begin to form a compact cluster, and if the tempera- 

 ture of the air surrounding them continues to drop they begin to gen- 

 erate heat within the cluster, often reaching temperatures consider- 

 ably higher than those at which they were formerly quiet and satis- 

 fied. It is evident, therefore, that the temperature within the cluster 

 is far from being uniform in winter, as has been, in a sense, assumed 

 among practical beekeepers. At the temperature at which other in- 

 sects 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 of a colony of undisturbed broodless 

 bees is above 57° F. and below about 69° F. the bees are quiet and 

 their temperature drifts with the outer temperature; at lower tem- 

 peratures they form a compact cluster, and the temperature within it 

 is raised by heat generated by the bees. 



The authors desire to state that while the lower critical point, 

 57° F., appears rather well established, the observations 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 win- 

 ter causes a marked increase in heat production and constitutes a 

 condition which may become one of the most disastrous that can be- 

 fall a confined colony. This will be discussed at a later time. 



When the heat production of the colony is explained, we are able 

 to understand to some extent the divergence 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 abnormal, due to disturbance, the chief difficulty in under- 

 standing the phenomena which take place is due to insufficient ob- 

 servations. For example, if between noon November 13 and 2 p. m. 

 November 15 only a half dozen temperature records had been made 

 for the cluster (and perhaps without finding the warmest part of it) 

 and the outside air, it would have been impossible to determine the 

 limits of heat production. Most observers have been satisfied with 

 a few observations, and seemingly everyone who has inserted a ther- 

 mometer in a hive has felt called upon to publish the results, thereby 

 only confusing the problem. 



THE EFFECT OF CONFINEMENT AND THE ACCUMULATION OF 



FECES. 



Before beginning a discussion of the effect of confinement and the 

 accumulation of feces, it may be recalled that during the active 

 summer season the length of life of worker bees is in a sense deter- 



