664 THE STUDY OF INSECTS. 



paper, although this was probably the first time in these 

 yellow-jackets' history that such a problem in architecture 

 had occurred. When these wasps wish to enlarge their 

 nest they tear away the inner layers of the envelope, add to 

 the sides of the comb, and put on new layers on the out- 

 side of the envelope. The yellow-jackets that build their 

 habitation in the ground excavate a hole which is enlarged 

 gradually as the colony grows. 



Superfamily APINA (A-pi'na). 

 The Bees. 



The bees can be distinguished from all other Hymenop- 

 tera by the form of the basal segment of the hind tarsi (Fig. 

 737, c). This segment is more or less dilated, flattened, and 

 generally hairy, and bears an apparatus for collecting and 

 carrying pollen. In the inquiline bees, however, this seg- 

 ment is narrower, and is not furnished with organs for col- 

 lecting and carrying pollen. 



Sometimes, in the case of those species that most closely 

 approach the wasps in structure, it is difficult to dis- 

 tinguish bees by a study of the tarsi alone. But 

 there is a microscopic character which is said to be 

 reliable even in these cases. It is said that the bees 

 differ from all other Hymenoptera in the form of the 

 hairs clothing the body, which, at least those of the 

 thorax, are branched or plumose (Fig. 793), while in 

 all other members of the order they are simple. 



The different species of bees exhibit great varia- 

 tions in habits: some are solitary, each female pro- 

 viding a nest for her young ; some are inquilines, 

 laying their eggs in the nests of other bees; and a 

 FlG- 793 ' few are social, of which the honey-bee is the most 

 familiar example. But in all the nest is provisioned with 

 pollen or honey, or both. In this respect the bees differ 



