HYMENOPTERA 939 



polymorphic than the sexual forms. 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. And with the honey-ants in some of the workers, the 

 repletes, the gaster is a large spherical sac, being distended by the 

 crop which is used as a reservoir for storing honey-dew to be used 

 later by the colony . 



Although all ants are social, great differences exist among them 

 as to the size of their colonies. In the more primitive species the 

 fully developed colony consists of only a few dozen individuals with 

 comparatively 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 exca- 

 vated material. These mounds are very familiar objects in many 

 parts of our country. 



A striking difference between the nests of ants and those of wasps 

 and bees is that the ants do not construct premanent cells for their 

 brood. The eggs, larvae and pupse are stored in chambers of the nest 

 and are moved from one to another in order to take advantage of 

 the changes in temperature and moisture. Thus the brood may be 

 brought near the surface of the nest during the warmer portion of the 

 day and removed to deeper chambers at nightfall. 



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 species, build in cavities of living plants; and still others, as 

 Cremasto gaster, build carton nests. 



Large swarms of winged ants are often seen. These are composed 

 of recently matured males and females that have emerged at the same 

 time from many different nests, probably from all of the nests of the 

 particular species involved that exist in the immediate region, and in 

 which young queens and males have been developed. The object of 

 these flights is mating, and they render probable the pairing of males 

 and females from different nests, thus preventing too close inter- 

 breeding. The factors that determine the occurrence of the nuptial 

 flights from all the nests of a species in one locality at the same time 

 are not understood. In the case of those species in which the female 

 is wingless, the mating must take place either in the nest or on the 

 groimd outside. 



