THE SOCIAL INSECTS 



have a special caste of large workers with enormous heads. 

 These are supposed to act as seed-crushers, making the food 

 available for the smaller ants who do all the collecting. 



LEAF-CUTTING ANTS 



The most elaborate agricultural operations are undertaken 

 by the leaf-cutting ants. These grow special fungi on frag- 

 ments of leaves or flowers which they carry into their nests 

 and store in underground chambers. Leaf-cutting ants are 

 found in America, from Texas to Patagonia, but are most 

 numerous in the tropics of South America. There are many 

 species, and there is a considerable range in structure and 

 behaviour. It will suffice here to describe the largest and most 

 specialised type, which belongs to the genus Atta. 



In most parts of South America nothing is more familiar 

 than the processions of the leaf-cutter or parasol ants. Each 

 worker is carrying a fragment of leaf or flower, held upright 

 over its head, " like Sunday-school children carrying ban- 

 ners " as the Rev. McCook remarked in one of the early 

 accounts of their habits. In many districts they are a serious 

 menace to agriculture, since they strip all the leaves of 

 plantations, often seeming to prefer the non-native vegetation 

 grown by the farmer. The colonies are of very large size, 

 with well-beaten paths radiating in all directions from the 

 nest. The nest consists of large irregular mounds of earth 

 several feet high and 20 or 30 feet across. The entrances are 

 as large as rat-holes, and there often seem to be long under- 

 ground passage-ways leading to points more than 100 feet 

 from the nest. The underground part of the nest extends 

 downwards for 10 feet or more, and contains a large number 

 of fungus-chambers connected by wide galleries. The 

 chambers are quite large, perhaps a foot or more high and 

 1-4 feet wide. They may be connected to the surface by 



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