HYMEN OPT ERA 



373 



Wasps of the genus Bembex. — These are stout-bodied wasps, usually 

 black with greenish or greenish-yellow bands. They burrow in the sand 

 and provision their nests with flies. Some species at least practise pro- 

 gressive provisioning. After excavating its burrow and making a cell, 

 the wasp captures a fly and stings it to death, then places it on the floor 

 of the cell and attaches an egg to it. After the larva has hatched, the 

 mother collects flies from day to day, feeding the larva till it is ready to 

 change to a pupa, closing the nest behind her each time she leaves it. 



A common and well-known related wasp in the South is Sticta Carolina 

 which is called the " horse guard." This is a large species which hunts 

 about horses in order to capture flies. 



THE BEES 



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 summer 

 day. An authority 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 Hymenoptera, except a few vespoid 

 wasps, 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 

 transported to the nest in the crop. While in the crop the nectar undei- 

 goes a chemical change, which is probably 

 due to a mixture with it of a ferment de- 

 rived from the salivary glands, and becomes 

 what is known as honey. 



A characteristic of bees found in only a 

 few other Hymenoptera is the presence, espe- 

 cially on the thorax, of plumose hairs. 

 Many forms of these hairs exist; some of 

 them are represented in Figure 621. It has 

 been suggested that the plumose 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 gather pollen ; 

 they are lacking, however, in some parasitic 

 bees. 



Female bees, excepting those of the genus 

 Prosopis and of the parasitic bees, are fur- 

 nished with pollen-brushes or scopes, for collecting and transporting pol- 

 len. In most bees these consist of brushes of hairs borne by the hind legs, 

 but in the Megachilidae the brush is on the ventral side of the ab- 

 domen. 



In some bees the pollen brushes are restricted to the tibia and the 

 metatarsus of the hind legs, in others they are borne on these two seg- 

 ments and on the femur, trochanter and coxa as well (Fig. 622). With 

 the queens and workers of the nest-building bumblebees and with the 

 workers of the honey-bee the pollen-carrying apparatus is very highly 



a b 



f 



Fig. 621. — Hairs of bumblebees. 

 (After John B. Smith.) 



