THE SOCIAL INSECTS 



looking like a small comb, may be dug up by the entomolo- 

 gist, the comb has not been built up, cell by cell, as in a 

 wasps' nest. Rather the superfluous earth has been removed, 

 and a group of six to twelve cylindrical cells has been isolated 

 in a small underground chamber. The earth is strengthened 

 by a coating of saliva. In Halictus the cells are composed of 

 that earth which the bees have not carried out of the nest, 

 whereas in a social wasp the cells are built of new material 

 which has been brought into the underground chamber. The 

 nearest human analogy is seen when a dug-out is compared 

 with a house. 



The great number of species of Halictus, many of which 

 are extremely similar to one another, suggest that the group 

 has evolved recently and is probably still evolving. It cannot 

 therefore be regarded as ancestral to the other social bees, 

 since these have a long history of social life. But Halictus 

 may be regarded as illustrating how social organisations in 

 bees may have originated. In them, the process has not yet 

 evolved very far. 



Rudimentary social behaviour approaching that of Halictus 

 occurs in some other bees of groups which are mostly solitary. 

 Such are the South African species of Allodope which build 

 nests in hollow plant stems. There are no proper cells and 

 the brood lies in a rather disorderly mass with the different 

 stages mixed together. The colony is begun by a single 

 female, but later her daughters help in obtaining food for 

 the brood. So much was established by Dr. H. Brauns, for 

 long a successful observer of African insects. Clearly this 

 example needs much more detailed study before it is fully 

 understood. 



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