SOLITARY AND SOCIAL BEES 



nest and less capable of reproduction, so that a worker caste 

 was produced. The stages of this history are much less well- 

 known in bees than in wasps, since fewer of the primitive 

 types of colony have survived. Social bees seem to have 

 started their evolution a longer time ago and to have pro- 

 gressed further, and the simpler types of colony have now 

 largely become extinct. 



Nevertheless, one of the more primitive types, the genus 

 Halictus, does still exist and is represented by a vast number 

 of species all over the world. Thirty-six are found in Britain 

 and a much larger number in the United States. For reasons 

 which will appear in a moment the fact that they are social 

 was quite unsuspected until about 1923, and many of the 

 details of their organisation are still little understood. One 

 of the chief difficulties in their study has been the large number 

 of species, many of them very alike, especially in the female 

 sex. Many species will often nest together in one bank of 

 earth, and in any ordinary locality in southern England one 

 may expect to find at least sixteen species. Another trouble 

 is the variety of their behaviour, not only when different 

 species are compared but within a single species either in 

 different parts of Europe or in different years. 



Some species are really solitary. Thus in Halictus xantho- 

 pus both males and females may be found flying together in 

 the home counties during the spring or early summer. Each 

 female after fertilisation enters winter quarters in a hole in 

 the ground. Early next spring she excavates a nest and raises 

 a brood of males and females. The males die soon after 

 mating, while the young females hibernate. Thus there is 

 one generation a year and it flies early. In the same species, 

 in Germany, both males and females may be found flying in 

 the autumn. Probably here there are two complete genera- 

 tions in the year, the females of the second one surviving 



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