226 INSECTS. 



and each ring of the abdomen fringed with grey or 

 whitish hairs. 



The Colletes are gregarious, and form large colonies. 

 They burrow in the softer parts of walls or in sand- 

 banks. The burrows, or tubular cells, are from eight to 

 ten inches long, and the extremity is plastered inside 

 with a thin coating of some substance the nature of 

 which is not fully ascertained, though it is supposed to 

 be a secretion of the insect. In substance it resembles 

 fine goldbeater's skin, and it seems to be laid on in a 

 soft or fluid state by the little trowel-like tongue. 



The burrow being completed, an egg and a store of 

 food composed of pollen and honey is deposited, and a 

 cell is formed by sealing up the portion of tube filled 

 with a flat wall of tbe same substance as that which lines 

 the sides. A second and concave wall is then built and a 

 second cell filled and furnished in the same way, till a series 

 of thimble-shaped cells are formed. It is believed that the 

 little mother is not always satisfied with a single burrow. 

 The wings of Colletes have three submarginal cells. The 

 species are from one-eighth to a quarter of an inch long. 



The genus Prosopis differs from Colletes in its 

 solitary habits as well as in appearance. Nearly naked, 

 and without apparent means of collecting pollen, it 

 has been supposed to be parasitic upon some indus- 

 trious Bee ; but while Mr. Smith's researches go to esta- 

 blish as fact that no species of the Andrenid is parasitic, 

 it is now known that Prosopis forms cells (plastered, as 

 by Colletes) in the stems of the bramble, rose, or other 

 plants, which they render tubular by excavating the soft 

 pith, and in which they make cells resembling those of 

 the former genus. 



The species of Prosopis are black, generally with 



