290 ANIMAL LIFE 



Towards the end of summer the colony, which at 

 its richest and most prosperous phase contained 

 from 300 to 400 individuals, shrinks to a third of 

 that population. In autumn the drones and workers 

 completely die out, and of the queens, a few hidden 

 in crevices are all that are left of summer's host. 

 Boys, mice, shrews, and a host of parasites ravish the 

 nests, and the moulds complete the work of destruction. 

 The bumble-bees, therefore, have not solved the crucial 

 problem of insect life, namely, how to extend longevity 

 and lessen the ravages of winter. But in the care 

 of their young they have made immense advance 

 over the solitary bees. The conversion of the first 

 brood into workers that systematically remain attached 

 to their birthplace or move together to a new site, 

 is the foundation of the caste system. Wax is made 

 use of for the first time, though carelessly and in 

 a more or less irregular pot-shape. Reservoirs for 

 honey are constructed. Ventilation is improved, and 

 a distinction made between the nutrition of the first- 

 formed workers and of the later drones and queens. 



In all these methods the social bumble-bees have 

 improved on the solitary, banded Halictm, as did this 

 on the simple Andrena and short-lived Prosopis ; 

 and the line of improvement is for the most part just 

 that which the hive-bee has brought to such a high 

 degree. 



In this evolution we have referred more than once 

 to the impetus given by exceptionally good seasons 

 or surroundings, and have pointed out that it was in 



