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, 
1 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 
