200 SCIENCE REMAKING THE WORLD 



sun, and whose individuals have no special social re- 

 lations with other individuals of the same kind. The 

 butterflies are good examples of these individualistic 

 insects. Their specialized associations are more with 

 the flowers than with other insects even of their same 

 kind. However, there are a few species of gregarious 

 butterflies whose individuals come together occasionally 

 in large swarms for some reason not well understood. 

 The familiar large reddish-brown monarch or milkweed 

 butterfly (anosia archippus) is such a gregarious butter- 

 fly. I have seen tall Monterey Pine trees on Point 

 Pinos near Monterey, California, simply covered by 

 thousands of these conspicuous butterflies, hanging to 

 the branches and to each other in long festoons. This 

 butterfly species has, too, the habit of migrating 

 occasionally in immense swarms. 



SOCIAL BEES. Such gregariousness is exhibited also 

 by certain mining bees which sometimes make their 

 nest-burrows, a single burrow for each mother bee, in 

 large numbers close together in some clay bank. Other 

 kinds of mining bees carry this nesting association a 

 step farther, in that several mother bees will combine to 

 dig a common vertical burrow and then each will build 

 a short side tunnel branching oflF from the common en- 

 trance tunnel for its own eggs and the stored food for 

 the larva which are to hatch from them later. 



The next step in this progress of the bees toward a 

 jsocial life, at least a family social life, is shown by the 

 bumble-bees. With all the bumble-bee species a few 

 fertilized fertile females or "queens," produced in the 

 autumn, go over the winter in concealment under 



