358 THE STUDY OF INSECTS 



Ants are easily recognized by the well-known form of the body. The 

 most distinctive feature is the form of the pedicel of the abdomen; this 

 consists of either one or two segments, and these seg- 

 ments are either nodiform or bear an erect or inclined 

 scale (Fig. 602). 



When the pedicel of the abdomen consists of a single 



ric. 602. . . , r . ., . . . f 



segment it is known as the petiole; when it consists 01 two 

 segments the first segment is termed the petiole and the second segment 

 the postpetiole. The swollen portion of the abdomen behind the pedicel is 

 known as the gaster. 



Another striking characteristic of ants is that in the antennas of 

 females and workers and of the males of some species the basal joint, the 

 scape, is long and the antennas are abruptly elbowed at the extremity of 

 this joint. 



The ants are all social insects, there being no solitary species. Each 

 colony consists of three castes, the males, the female or queen, and the 

 workers. As with the social bees and the social wasps, the workers are 

 all modified females. With most ants the males and the queens are 

 winged and the workers wingless; the wings of queens, however, are de- 

 ciduous. In certain genera that live as parasites in the nests of other 

 ants the worker caste is wanting, and in some species the females are 

 wingless. 



With many ants the polymorphism is not restricted to the presence 

 of three uniform castes for one or more of the castes may be represented 

 by more than one form. Of the males there may be either an unusually 

 large form, or dwarfs, or ergatoid males, that is, males that resemble 

 workers in having no wings and in the structure of the antennas. The 

 queens exhibit a similar series of forms; those of unusually large stature; 

 dwarfs which are sometimes smaller than the largest workers; and er- 

 gatoid queens, which are a worker-like form, with ocelli, large eyes, and a 

 thorax more or less like that of the normal queens, but without wings. 

 In many species the workers are of two distinct sizes, the worker majors 

 and the worker minors. In colonies that are founded by an isolated 

 female the first brood of workers is of the worker minor form. With 

 many species a worker form exists in which the head and the mandibles 

 are very large, the soldier caste. 



Although all ants are social, great differences exist among them as to 

 the size of their colonies. In the more primitive species the fully de- 

 veloped colony consists of only a few dozen individuals with com- 

 paratively feeble caste development ; while in the more highly specialized 

 forms a colony may consist of hundreds of thousands of individuals and 

 exhibit an elaborate polymorphism. 



The different species of ants differ also in their nesting habits. By 

 far the greater number of species excavate their nests in the ground. 

 Certain species are often seen burrowing in paths or other open places; 

 but many more are to be found under small flat stones or other objects 

 lying on the ground. Some species, especially those in which the colonies 

 become large, build large mounds of the excavated material. These 

 mounds are very familiar objects in many parts of our country. 



While most species of ants nest in the soil, there are many that build 

 their nests in wood, in timbers, in the trunks of decaying trees, in or 

 under bark, or in hollow stems. Others, especially certain tropical spe- 



