HYMENOPTERA 979 



to pass and immediately thereafter resumes its guarding position 

 with its head closing the opening of the corridor. 



The explanation of this association of several bees, in a single 

 nest was worked out by Fabre. He found that in the spring each 

 female Haltctus that has survived the winter makes a nest and rears 

 a brood. Then the old bee and the young ones together clean out 

 the nest, enlarge it, and use it as a carefully guarded apartment house, 

 each bee having her own group of cells. 



Halictus {Augochlora) . — A detailed account of the habits of one 

 species of this subgenus, A. humerdlis, was given by Professor J. B. 

 Smith ('oi). This species is a mining bee which digs very deep 

 burrows. Certain other species of this genus have very different 

 nesting habits. These burrow in decomposing sap-wood beneath 

 the bark of trees and make their cells of bits of decayed wood agglu- 

 tinated together. 



Anthophora. — The genus Anthophora is widely distributed and 

 includes many species, more than eighty have been described from 

 North America alone; but the habits of only a few of these have 

 been described. 



The nests of those American species the habits of which are well 

 known are usually built in steeply inclined or perpendicular banks of 

 earth, preferably in those of compact clay; they are also excavated 

 in the clumps of clay held between the roots of stumps in stump- 

 fences. In the West a favorite nesting place of these bees is in the 

 walls of sun-dried bricks of the adobe houses. Like Halictus and 

 Andrena, the bees of this genus are gregarious, hundreds of individuals 

 building their nests close together in the same bank of earth. 



A striking feature of these nests is the presence of a cylindrical 

 tube of clay extending outward and downward from the entrance of 

 the tunnel (Fig. 1222). This tube is rough on the outside but smooth 

 within. It is composed of small pellets of earth compacted together. 

 These pellets when brought out from the tunnel are wet and easily 

 molded into the desired form, but soon become dry and firm. The 

 wetness of the pellets of clay brought out from the tunnel in a hard dry 

 bank is explained by the fact that these bees when nest-building go 

 to some place where water can be had and after lapping up a supply 

 of it fly to their nest. This water is obviously used for softening the 

 hard clay (Frison '22). 



The tunnel extends into the bank a variable distance and leads 

 to a cluster of oval cells. The layer of earth forming the wall of a cell 

 is made firm by some cementing substance; this is shown by the fact 

 that when a lump of earth containing nests is broken apart the cells 

 retain their form and may be readily separated from the earth sur- 

 roiinding them. Nininger ('20) in his notes on the life-history of 

 Anthophora stanfordidna state: "At the bottom of a tunnel five to 

 seven inches deep, the bee excavated an oval chamber about three- 

 fourths inch in diameter by one inch deep, and then built up within 

 this a nest-cell to fit, made of pellets of clay and worked smooth on 

 the inner side, after which it was coated with a thin layer of water- 

 proofing which seemed to be a salivary secretion." 



