SOCIAL LIFE 239 



Among many ants of the same species the workers of a 

 community differ among themselves so that two or more 

 definite types or castes are recognisable. These are usually 

 adapted for performing special functions in the social life 

 so that the communities practise a " division of labour." 

 For example, there may be workers with abnormally large 

 heads armed with powerful mandibles ; such in some 

 societies are the so-called '' soldiers," '' policemen or 

 defenders of the colony," while in certain harvesting or 

 hunting ants their work is " to crush seed or the hard parts 

 of insects so that the softer parts may be exposed and eaten 

 by the smaller individuals." Among the well-known 

 " leaf- cutting ants " of the American tropics (Atta and 

 allied genera), whose object in collecting and dividing the 

 leaves was first detected by T. Belt (1874) as the provision 

 of a soil on which to raise in the underground chambers of 

 their nests the fungi on which they feed, there are in many 

 species large-headed workers which carry out the spectacular 

 raiding expeditions in the forests and bear away the leaves 

 into the nests, where smaller workers with heads of normal 

 form act as ** mushroom- gardeners " in the deeply situated 

 cavities where the food of the community is actually grown. 

 A striking feature noticeable in most ant communities is 

 the close correspondence between the modifications of the 

 workers and the nature of the food. Among the 

 " legionary " or " driver " ants — which include the African 

 and Oriental Dorylus (Fig. 61) and Anomma, and the tropical 

 American Eciton and allies — the communities range over 

 the country often in huge swarms attacking insects, spiders 

 and sometimes even large vertebrates which furnish their 

 food. The workers are blind, guided on their forays 

 through their senses of touch and smell, varying greatly in 

 size, the larger castes with great broad heads, armed with 

 long trenchant mandibles. The picturesque account of 

 T. S. Savage (1847) ^^^ been confirmed by later observers. 

 He described " an arch for the protection of the [smaller] 

 workers constructed of the bodies of their largest class," 

 whose '* widely extended jaws, long slender wings and 



