THE IMPORTANCE OF SOCIAL LIFE 75 



Definite grouping is often shown although no organiza- 

 tion is apparent. Lady beetles assemble in huge masses in 

 the fall, sometimes completely covering rocks or logs or 

 holes in the ground. The advantage may be in the gain in 

 warmth, for even cold-blooded animals show some slight de- 

 gree of temperature above the surroundings. The advantage 

 of grouping cannot, however, explain the way the collections 

 start. Are they started accidentally, or by leadership, or by 

 some directing chemistry? We do not know. The process 

 does, however, bring about grouping of members of one 

 species. Schools of fishes form in some species, and there 

 does not seem to be any particular advantage. Chemical 

 studies of the water around and in such schools has never 

 revealed any differences, and the fish change direction as 

 a body very erratically. It seems that some of the fish that 

 form schools join in the grouping simply because other fish 

 of their kind are there, for companionship. Enormous swarms 

 of insects with incredible powers of destruction have more 

 than once endangered the very existence of man's societies. 

 Male midges in great numbers dance in swarms, perhaps 

 awaiting their females. Some solitary bees gather at night in 

 groups for males only. There are butterfly species which 

 meet night after night in the same place. Alale robins in the 

 off-season form large flocks. Some birds migrate in large 

 groupings, some in smaller, as in the V-shaped flights of 

 geese. The cases are innumerable, and for many one can 

 show little, if any, advantage. The assumption of natural, 

 innate tendencies toward social groups is decidedly permis- 

 sible. 



The lemmings of Norway are the classical example of an 

 unexplained mass behavior in mammals. These mouse-like 

 animals migrate periodically in hordes, eating their way 

 across the country, crossing rivers, and finally plunging into 

 the sea to their death. They live in the mountains of Nor- 

 way, near the timberline, where they ordinarily produce 

 one or two litters each summer, a rate that maintains a 



