346 Beekeeping 



the temperature, by abundant ventilation or by artificial 

 drying, as by the use of unslaked lime. These methods 

 may be applied in the bee cellar. It should be recalled that 

 an increase in the temperature of the atmosphere increases 

 the capacity of the atmosphere for water vapor and thereby 

 decreases the relative humidity. 1 



Bees need water in winter but they get enough in their 

 food provided the temperature does not get so high that 

 the relative humidity of the outer air is too low. The 

 optimum relative humidity has not been determined and, 

 in fact, virtually no observations have been made on the 

 relative humidity of the atmosphere of the hive or bee cellar. 

 Probably the great diversity of opinion as to the best tempera- 

 ture for the bee cellar is due to the unrecorded differences 

 in the relative humidity of the various cellars observed. 



Effects of ventilation. 



Ventilation of the hive and of the bee cellar depends upon 

 the currents of air caused by the differences in temperature 

 in two points, since bees do not mechanically ventilate 

 the hive in winter. The movements of air serve not only 

 to remove carbon dioxid and bring in oxygen but, probably 

 more important, they carry out the surplus water vapor. 

 Abundant ventilation is beneficial and becomes harmful 

 only if the temperature is too greatly reduced thereby. It 

 has been determined that bees survive in an atmosphere 

 which contains an unusually high percentage of carbon dioxid 

 but it is not wise to err on that side. 



Source of heat and effects of changes of temperature. 



It has been determined by Demuth and the author 2 that 

 bees generate heat in winter by muscular activity and that 



1 The beekeeper interested in cellar wintering will do well to consult 

 Marvin, 1912, Psychrometric tables, Weather Bureau Publication 235 

 and other works dealing with the relation of relative humidity to tempera- 

 ture. 



2 Phillips and Demuth, 1914. The temperature of the honey bee cluster 

 in winter. U. S. Dept. of Agric., Bulletin 93. 



