972 



AN INTRODUCTION TO ENTOMOLOGY 



Tribe CRABRONINI 



In the Crabronini the postscutellum and the base of the propodeiun 

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

 marjj;ins 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 svmiac 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). 



Fig. 1212. 

 — Crabro. 



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 propodeum (Fig. 12 13). The inner 

 margin of the e^-es is convex, not converg- 

 ing toward the clypeus; and the longi- 

 tudinal free part of vein M is lost or 

 present as a trace. 



These wasps nest in sand and provision 

 their nests with flies. 



Fig. 1 2 13. — Metanotum and 

 propodeum of Oxybelus: 

 sq., squama; sp., spine. 



THE BEES 



Superfamily Apoidea of Authors 



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

 the well-known honey-bee and the bimiblebees thousands of ot-ier 

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

 summer day. Friese ('23) states that 12,000 species of bees have been 

 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 H^'menoptera, except some members 

 of a small subfamily of vespoid wasps, the Masarince, 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 due to a mixture with it of a 

 ferment derived from the salivary glands, and becomes what is 

 known as honey. 



