HYMENOPTERA 977 



species, are small black bees, with pale, usually yellow, marks. They 

 are the least specialized of the bees. The body is almost bare, but an 

 examination with a microscope will reveal the presence on the thorax 

 of a few of the plumose hairs characteristic of bees; the labiimi is 

 short and broad and shallowly emarginate at the apex (Fig. 12 17) 

 and the hind legs of the females are not furnished with pollen brushes. 



The numerous species of this genus build nests in the stems of 

 pithy plants, or in burrows in the ground, or in crevices in walls. 

 I have found them in dead branches of simiac. In some cases, at 

 least, the burrow used was an old burrow made by some other pith- 

 mining bee or wasp. After the burrow is made or selected, the walls 

 of it are coated with a glistening substance, probably silk, which is 

 sometimes dense enough to form a distinct membrane. Then a cell 

 is formed at the bottom of the burrow of the same material ; and at 

 the bottom of the cell a denser circular disk is spun, which makes a 

 quite firm partition, the edges of which extend slightly up the sides 

 of the cell. 



The cell is provisioned with a semi-liquid paste consisting largely 

 of honey but containing also some pollen. It is said that when collect- 

 ing provisions for its nest the bee swallows both pollen and nectar, 

 brushing the pollen to the mouth by aid of the front legs. 



Usually several cells are made, one above another, in the burrow; 

 although the walls of the cells are quite delicate, the cells are firmly 

 separated by the dense silken partition at the bottom of each. 



Subfamily COLLETIN^ 



In this subfamily the labium is short, and deeply emarginate at 

 the apex; (Fig. 12 18), The body, especially the head and thorax, is 

 more or less densely clothed with hair; and in the female the hind 

 legs are furnished with pollen-brushes. Our most common repre- 

 sentatives belong to the genus Colletes. 



Colletes. — In most species of this genus the abdomen is marked 

 with pubsecent white bands. All of the species, the habits of which 

 have been described, burrow in soil, either that which is level or in 

 banks, or sometimes in the interstices of walls. In favorable situ- 

 ations, some of the species are gregarious, many individuals digging 

 their tunnels in a limited area. Sharp ('99) in writing of Colletes 

 states : "They have a manner of nesting peculiar to themselves ; they 

 dig cylindrical burrows in the earth, line them with a sort of slime, 

 that dries to a substance like gold-beater's skin, and then by partitions 

 arrange the burrow as six to ten separate cells, each of which is filled 

 with food that is more liquid than usual in bees." 



Professor J. B. Smith ('01) in his account of Colletes compdcta 

 states that this species digs a burrow which extends from 18 to 28 

 inches down; from this, lateral branches from two to six inches in 

 length are made, at the end of each of which a cell is formed. The 

 bee begins making cells from the bottom of the burrow and works up, 

 never making more than four and rarely more than two cell-bearing 



