26 INSECT ARTIZANS AND THEIR WORK 



from the underground cells where they have lain 

 dormant through the winter. There is this differ- 

 ence in the habits of Halictus and Andrena, that 

 certain work is done by Halictus in common. A 

 number of females unite in excavating the shaft, 

 and then each one builds her own set of cells 

 unaided. Instead of each cell being a separate 

 chamber opening out of the shaft at different 

 levels, the cells of one worker form a mass in a 

 common vault — an enlargement of one part of 

 the shaft which, however, is continued far below 

 the level of the vaults. The object of this down- 

 ward extension is probably the better drainage of 

 the vault. The entrance shaft is only wide enough 

 for one bee to pass in or out at one time, but as 

 several workers are engaged, this would lead to 

 much loss of time and confusion if special provision 

 were not made. This takes the form of an enlarge- 

 ment of the width not far from the entrance, and 

 allows two bees going in opposite directions to pass 

 each other. Some species make branch corridors 

 from which the vaults of each worker open. The 

 cells are oval and lined within by a coat of liquid 

 silk or varnish. The winged bees emerge from 

 these cells in September ; but the males are all 

 killed by the autumn frosts, whilst the females 

 continue to live underground through the winter, 

 emerging from their mine-shafts in spring and 

 setting to work at once to enlarge the colony or 

 to start new ones. Their mining operations are 

 pursued at night, especially in moonlight. 



