HYMENOPTERA 375 



The different species of bees exhibit great differences in habits; some 

 are solitary, each female providing a nest for her young; some are para- 

 sitic, the females laying their eggs in the nests of other bees and the 

 larvae feeding on the provisions stored by their hosts; and some are 

 social, living in colonies consisting of many individuals. 



The nests of solitary bees, like those of the digger-wasps, are of many 

 forms. The mining-bees dig tunnels in the ground; the mason-bees build 

 nests of mortar-like material; the carpenter-bees make tunnels in the 

 stems of pithy plants or bore in solid wood; and some bees make nests of 

 comminuted vegetable matter. The distinctive characteristic of the 

 nests of bees is the fact that they are always provisioned with honey and 

 pollen. In many cases closely allied species of bees differ in their nesting 

 habits; for example, different species of the genus Osmia build very 

 different kinds of nests. 



The social bees are the honey-bees, the bumblebees, and the stingless 

 honey-bees of the Tropics. In all of these, as with the social wasps and 

 the ants, there is in addition to the males and the egg-laying females a 

 worker caste ; with all other bees there are only two forms, the males and 

 the females. 



Family Andrenid^e 



The Andrenids 



The family includes those solitary nest-building bees and their para- 

 sitic allies in which the tongue is either short or long but is pointed at the 

 apex, and in which the pollen-brushes of the nest-building females are borne 

 by the hind legs. To this family belong a large portion of the species and 

 genera of our bees. Space can be taken here to discuss only a few of these. 



Halictus. — Among the more common of our mining bees are those of 

 the genus Halictus. This is a large genus including very many species, 

 among which are the smallest of our bees. The nests of some species are 

 excavated in level ground; other species dig tunnels in the vertical sides 

 of banks. These bees are often gregarious, hundreds of nests being built 

 near together in the side of a bank. 



If these nests be studied in midsummer, each will be found to consist 

 of a burrow extending into the bank and, along the sides of this main 

 burrow or corridor, smaller short burrows each leading to a cell, the sides 

 of which are lined with a thin coating of firm clay (Fig. 626). In each of 



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Fig. 626. — Diagram of part of a nest of Halictus. 



