HYMENOPTERA 995 



laterals from one upright. How many such burrows an individual 

 female may make was not determined. 



Family ANDRENID^ 

 The Andrenids 



The family includes those solitary nest-building bees and their 

 parasitic 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. 



HalictMs. — 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 



Fig. 1 22 1. — Diagram of part of a nest of Halictus. 



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 (Fig. 1221) 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. In each of these cells that is closed will be found either a 

 mass of pollen and nectar with an egg upon it or a larv^a feeding on 

 the food stored for it. 



The most striking feature of these nests is the fact that several 

 bees use the corridor as a passage way to the cells they are building 

 and provisioning. But this corridor is not a public one; it is con- 

 stricted at its outer end and is guarded by a sentinel whose head 

 nearly fills the opening. When a bee comes that has a right to enter 

 the sentinel backs into the wider part of the corridor and allows it 



