360 APPLIED ENTOMOLOGY 



similar places, are generally called hornets, though there is really no 

 sharp distinction between them and yellow-jackets, in the usual use of 

 these names. The life of the colony in the case of these insects does not 

 differ from that of the forms described above which make only one 

 layer of cells with no outside wrappings (Polistes), but in the yellow- 

 jackets and hornets the colony increases much more rapidly and by fall 

 may number several hundred individuals. 



Taking the wasps as a whole, we find an interesting progressive 

 development in the different groups. As regards their habitations, we 

 may perhaps regard the holes dug in the ground as being the simplest, 

 followed by excavations of the pith of woody stems, the construction 

 of mud nests and finally along this line the formation of artistically 

 shaped urns, as progressive steps in architectural ability. The con- 

 struction of hexagonal cells of paper pulp, first in a single layer, then in 

 several layers surrounded by a paper wrapping and finally much more 

 substantially built to resist exposure to the weather above ground may 

 be regarded as continued progress in this line, the nest of the hornet 

 marking the climax of the series. 



Somewhat parallel to this is the nature of the food. The nests 

 in the ground, in plant stems, and in mud cells, are provisioned with 

 insects stored as food for the young of the forms constructing them: 

 in other words these wasps are parasitic insects. With tiie appearance of 

 cells of paper pulp the food changes to a mixture of insects killed and 

 partly chewed up, and of plant materials such as pollen. At this same 

 point also, a change from a solitary to a colonipJ life begins and as the 

 colony becomes larger the nest increases in size and strength. 



There is therefore a progressive development in the insects of these 

 Superfamilies, illustrated in nest structure, food, and the advance from 

 solitary life to that of a large colony. 



Superfamihj Apoidea (The Bees). — The bees familiar to everybody, 

 are the bumblebees and the honey bee, but these form a very small part 

 of the insects belonging in this superfamily. Many of the bees are 

 solitary in their habits; are rather small insects and little attention 

 is paid to them. They are important insects, however, valuable to man 

 as they visit flowers and cross pollinate the blossoms. 



The bees have the first segment of the hind tarsus somewhat enlarged 

 and flattened, and in those which carry pollen there, hairs are present 

 to aid in this. In addition, the hairs on the thorax are branched or 

 plumose while in the other Hymenoptera they are simple. 



Some of the bees are solitary (Fig. 382) and dig holes in the ground, 

 generally with side pockets in which pollen or pollen and honey are 



