264 AN INTRODUCTION TO ZOOLOGY 



the flower. Certain observations apparently prove that smell 

 and not color is the dominant factor (217), whereas other ob- 

 servations have resulted in the conclusion that insects, such as 

 bees and butterflies, that show a high degree of adaptation to 

 flowers, prefer red, purple, and blue, and that insects poorly 

 adapted to flowers favor yellow and white (213). Perhaps the 

 safest view to adopt at present is that color, odor, and structural 

 characters are all important factors influencing the visits of bees 

 and other insects to flowers (204, 208). 



d. The Social Life of Bees 



Certain species of ants, bees, and wasps exhibit, as in the case 

 of the honeybee, remarkable social organizations. How this 

 has come about is a problem not yet solved, but practically all 

 stages, from a solitary habit to a complex community, are illus- 

 trated by various members of the family Apidae (199, 207). 



(1) A SOLITARY BEE. The leaf-cutter, Megachile acuta, is 

 a solitary, long-tongued bee. In building her nest she digs a 

 tunnel, usually in decayed wood, and excavates thimble-shaped 

 cavities in the bottom of it. These cavities are lined with pieces 

 of leaves, generally cut from a rose bush. In the bottom, the 

 bee places a quantity of pollen and nectar, upon which she lays 

 an egg. She then plugs the entrance with pieces of leaves, and 

 flies away. The young that hatch from her eggs live upon the 

 stored food. 



(2) A SOLITARY BEE THAT WATCHES ITS YOUNG. The car- 

 penter bee, Ceratina dupla, makes her nest by digging the pith 

 from the center of a dead twig of sumach or other plant. After 

 a long tunnel is excavated she begins at the bottom and constructs 

 a series of chambers with partitions composed of pith. At the 

 bottom of each chamber she places a mass of pollen and lays 

 an egg. She then waits for her offspring to emerge. " The 

 lower one hatches first; and, after it has attained its growth, it 

 tears down the partition above it, and then waits patiently for 

 the one above to do the same. Finally, after the last one in the 



