THE POLYMORPHISM OF ANTS.* 



By William Morton Whkkler. 



There is a sense in which the term polymorphism is apphcable 

 to ah hving organisms, since no two of these are ever exactly 

 alike. But when employed in this sense, the term is merely a 

 synonym of "variation, " which is the more apt, since polymorph- 

 ism has an essentially morphological tinge, whereas variation em- 

 braces also the psychological, physiological, and ethological differ- 

 ences between organisms. In zoology the term polymorphism 

 is progressively restricted, first, to cases in which individuals of the 

 same species may be recognized as constituting two or more 

 groups, or castes, each of which has its own definite characters or 

 complexion. Second, the term is applied only to animals in 

 which these intraspecific groups coexist in space and time and do 

 not arise through metamorphosis or constitute successive genera- 

 tions. Cases of the latter description are referred to "alternation 

 of generations" and "seasonal polymorphism." And third, the 

 intraspecific groups which coincide with the two groups of repro- 

 ductive individuals in all gonochoristic, or separate-sexed 

 Metazoa are placed in the category of "sex" or "sexual dimor- 

 phism." There remain, therefore, as properly representing the 

 phenomena of polymorphism only those animals in which char- 

 acteristic intraspecific and intrasexual groups of individuals may 

 be recognized, or, in simpler language, those species in which one 

 or both of the sexes appear under two or more distinct forms. 



As thus restricted polymorphism is of rare occurrence in the 

 animal kingdom and may be said to occur only in colonial or 

 social species where it is commonly attributed to a physio- 

 logical division of labor. It attains its clearest expression in 

 the social insects, in some of which, like the termites, we find both 

 sexes equally polymorphic, while in others like the ants, social 

 bees, and wasps, the female alone, with rare exceptions, is dift'er. 



* Abstract of an address before the Entomological Society of America 

 Decemlier 28, 190G, and pul>lished in full in the Bulletin of the American Museum 

 of Natural History, Vol. XXIII, Article I, Jan. 15, 1907, pp. 1-93, pll. I-VI. 

 Only the more general considerations are embodied in this abstract ; for a detailed 

 account of the effects of Orasema, Lomechusa, Xenodusa and Mermis parasitism 

 in ants, the reader is referred to the complete work. 



39 



