32 THE SOCIAL LIFE OF ANIMALS 



they die more readily, and frequently they repro- 

 duce less rapidly than if living in uncrowded popu- 

 lations. 



All the older works in natural history taught 

 fairly clearly that crowded groups, to have real sur- 

 vival values, must be sufficiently well organized to 

 contribute to group safety by warning of danger or 

 by defense in case of attack. (3) If, in addition, these 

 groups are organized on a basis of division of labor, 

 such as occurs in the highly social colonies of ants 

 or termites, with specialized reproductives, workers 

 and soldiers, or according to the patterns found in 

 human society, then the survival values of groups 

 are readily seen. 



Yet for some reason, under natural conditions and 

 with very many sorts of animals, crowding in all 

 degrees does occur and apparently always has oc- 

 curred. Conceded that animals do not always act for 

 their own best interests, still they must do so to a 

 certain degree or be exterminated in the long run. 

 The advantages of the long-established habit of a 

 species may not be obviously apparent, but it is not 

 safe to say offhand that advantages do not exist. 



There are the dense crowds of certain animals, 

 ladybird beetles (Plate la), for example, that with 

 the approach of winter collect in restricted and fa- 

 vorable places where they hibernate together. Ap- 



