io86 LIFE : OUTLINES OF GENERAL BIOLOGY 



in mind that of the 10,000 or so known species of bees, less than 

 500 are social, and these are all included in five genera. That 

 leaves 9,500 different kinds of solitary bees, differing from one 

 another in their tongues and hairs, nests and cells, and in their 

 relations to the flowers they visit and the family they rear. 



Among the solitary bees we may begin with those species in which 

 the mothers usually die after egg-laying and providing food for 

 their prospective young ones. They rarely survive to see the fruit 

 of their labours. Many make nests quite apart from their kindred, 

 but there are often anticipations of something else. Thus there may 

 be gregarious nesting; there may be mutual aid against attack; 

 two or more females may use a common hole of refuge. These are 

 straws that show how the evolutionary wind once blew. How sugges- 

 tive is a case where several females occupy separate nests, but make 

 a common entrance tunnel — a sort of "common stair"! Even more 

 significant are a few species in which the mother guards the eggs, 

 and may even survive to see the offspring emerge. In some kinds of 

 Halictus the fertilised females survive the winter and give rise to 

 a generation of daughters in the spring. These are parthenogenetic, 

 but their eggs develop into males and females in the autumn. The 

 males die after fertilising the females, which hibernate as we have 

 said. If the parthenogenetic daughters, produced in the spring, 

 remained at home to help their mother, there would be a step 

 towards a society. This step is actually taken in some very interesting 

 South African bees belonging to the genus AUodape, where the 

 daughters help their mother in provisioning and actually feeding 

 the next brood. Thus arises the co-operative family! 



But we must confess that a continuous story cannot be told at 

 present, for Prof. W. M. Wheeler points out, in his Social Life 

 among the Insects (1922), that the rudimentary societies of certain 

 species of Halictus and Allodape cannot be regarded as the actual 

 precursors of the social bees. They are interesting as stages, but 

 they are not on the direct line of social evolution. The ancestors of 

 the social bees remain unknown, though it cannot be doubted that 

 they were, or perhaps are, among the solitary bees. There are three 

 groups of social bees, the humble-bees (Bombinae), the stingless bees 

 (Meliponinae), and the honey-bees (Apinae). The first are the most 

 primitive, the last the most specialised, while the Meliponines (with 

 vestigial stings), that nest in hollow trees in warm countries, are 

 strange combinations of the primitive and the specialised. They 

 form permanent societies, but they make rather imperfect combs. 

 They are the only social bees that are linked back to the solitary 

 bees by the habit of rearing the brood of aU three castes (queens, 

 workers, and drones) in closed cells, never opened till the young 

 winged bee creeps out. 



The humble-bees of the Northern Hemisphere are of pecuhar 



