THE SOCIAL INSECTS 



the winter to renew the cycle in the following spring. In 

 the more favourable climate of southern Europe the males 

 may not only appear in the autumn but also hibernate and 

 appear again in the spring. By these conditions the same males 

 and females may fly both in the autumn and in the spring. 

 Other species, such as the common British Halictus morio, 

 seem to have more than one generation of males and females 

 during the summer, but almost invariably only the females 

 of the last generation survive the winter. In this species, the 

 seasonal picture is as follows: 



Spring Summer Autumn Winter 



Female Male and female Male and female Female 



DEVELOPMENT OF A WORKER CASTE 



Life histories of the type hitherto described are solitary, 

 but in some other species the spring female may survive 

 long enough to be found in the nest at the time when the 

 summer females, her daughters, are emerging. Though the 

 mother and offspring do not in this case co-operate in nest- 

 construction, there is here the first hint of social behaviour, 

 since the presence of the mother in the nest must give her 

 young some protection throughout their development. 

 Another group of species, including in Britain Halictus 

 calceatus and several very similar ones, have a real social 

 organisation. Males and females are found in the late summer 

 and autumn, but only the fertilised females hibernate to be- 

 come the spring females of the following year. The spring 

 females, either alone or working in small groups (up to three 

 females), construct a nest and produce offspring which are 

 all female. This brood of females may or may not be extern- 

 ally different from the spring-mother, but in any case they 

 are unfertilised ; their ovaries develop only to a limited 



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