HYMENOPTERA 989 



Tribe CRABRONINI 



In the Crabronini the postscutellum and the base of the prcpodeum 

 are unarmed; the eyes are usually much widened below, their inner 

 margins strongly converging towards the clypeus; and 

 the longitudinal free part of vein M of the fore wings is 

 complete. The head is generally large and square when 

 viewed from above, and sometimes broader than the 

 thorax (Fig. 12 12). 



The different members of this tribe vary greatly in 

 their nesting habits. Some mine in the pith of such plants 

 as sirmac and elder; some bore in more solid wood; some 

 dig burrows in the ground; and others make use of any 

 suitable hole they can find, often the deserted burrow of 

 some other insect. These insects usually provision their nests with 

 flies. 



The North American Crabronini was monographed by Fox ('95). 



Tribe OXYBELINI 



The Oxybelini are easily distinguished from all other sphecoid 

 wasps by the two squamae projecting back from the metanotum and 

 by a median spine borne by the base of 

 the propodeimi (Fig. 12 13). The inner 

 margin of the eyes is convex, not converg- 

 ing toward the clypeus; and the longi- 

 tudinal free part of vein A I is lost or 

 present as a trace. 



These wasps nest in sand and provision 

 their nests with flies. 



Fig. 1213. — Metanotum and 'PTTT? ■RTTTTc: 



propodeum of Oxybelus: ^ ^^ £.ilil^ 



sq., squama; sp., spine. 



Superfamily Apoidea of Authors 



The bees constitute a very large group of insects, including besides 

 the well-known honey-bee and the bumblebees thousands of other 

 species, many of which can be observed visiting flowers on any pleasant 

 simmier day. Friese ('23) statesthat 12,000 species ofbees havebeen 

 described, of which 2,500 are from North America and estimates that 

 there are 20,000 living species in the world. 



The bees differ from all other Hymenoptera, except some members 

 of a small subfamily of vespoid wasps, the Masarinae, in that they 

 provision their nest with pollen and honey instead of with animal 

 food, as do other nest-building Hymenoptera. The honey is obtained 

 from flowers in the form of nectar, which is swallowed and trans- 

 ported to the nest in the crop. While in the crop the nectar undergoes 

 a chemical change, which is probably di:e to a mixture with it of a 

 ferment derived from the salivary glands, and becomes what is 

 known as honey. 



