HYMENOPTERA 



973 



The distinctive characteristics of bees that have been recognized 

 are chiefly those that are correlated with the habit of collecting pollen 

 and nectar for provisioning their nests. These consist in specializa- 

 tions of the form and arrangement of some of the hairs, fitting them 

 for collecting and carrying pollen; in the dilation of the metatarsus 

 of the hind legs, which forms a part of the pollen-collecting apparatus ; 

 and in varying degrees of specialization of the maxillae and labium to 

 form a proboscis fitted for extracting nectar from flowers. 



These characteristics are easily recognized in the higher bees, but 

 in the most generalized bees (Prosopis) they are feebly developed, 

 and too as male bees do not collect and carry pollen to nests they do 

 not possess organs for this purpose; this is also true of both sexes 

 of the parasitic bees, the females of which have acquired the habit 



Fig. 1 2 14. — Hairs of various bees: a-f, of bumblebees; g-j, of Melissodes sp.; k-n, 

 of Megachile sp. (After John B. Smith.) 



of laying their eggs in the nests of other bees, and consequently, have 

 become degenerate so far as their pollen-collecting apparatus is con- 

 cerned. 



A characteristic of bees found in only a few other Hymenoptera 

 is the presence, especially on the thorax, of plumose hairs. Many 

 forms of these hairs exist ; some of them are represented in Figure 1 2 1 4 . 

 In this figure there is also represented (Fig. 12 14, n) another type of 

 hair which is spirally grooved; this type is found in the pollen brush 

 of leaf-cutter bees, Megachilidse. It has been suggested that the 

 plimiose hairs serve to hold the grains of pollen that become en- 

 tangled among them when a bee visits a flower; but they occur in 

 males and in parasitic bees neither of which gathers pollen; they 

 are lacking, however, in some parasitic bees. 



