ARMY ANTS — SCHNEIRLA 393 



bivouac first divides into limb columns, which in turn divide and re- 

 divide into branch coluimis, these finally into twig columns. The twig 

 columns end in small scurrying groups of foragers. 



The other main trail systems are similar, each with its base trail, 

 its branching and rebranching secondary trails. They differ only in 

 secondary details concerning the routes and distances, how much out- 

 going traffic pours into each, and how much booty is returned. All 

 these differences may influence which of these principal routes is to be 

 taken in the eventual emigration of the evening. 



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I. 



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Figure 3. — Left, raiding and emigration in the nomadic phase: B-1, Wednesday's bivouac 

 and emigration route to B-2, from which a complex 3-system raid developed on Thursday. 

 Thursday evening the colony emigrated about 350 meters to the new place, B-3, from 

 which a similar raid developed on Friday, and so on for 16 days, until the phase ended 

 with the enclosure of the larval brood. Right, sketch of a raid in the statary phase, when 

 the colony has an enclosed brood (passing through the pupal state) and is bivouacked in 

 a hollow log or tree. Raids are much smaller than in the nomadic phase. The statary 

 phase lasts 20 days and ends with the emergence of the pupal brood as new workers. 



The small groups of ants in the outskirts are the pioneers, first to 

 extend the raid into new territory, first to rush back, exciting ants in 

 the rear, when booty is found. Occasionally each such group divides, 

 as when it grows oversize or a natural obstacle is met, and a forking 

 of the trail results. In the train of each of these "pushing parties" 

 there is a two-way column joining its path with older routes in the 

 rear and eventually with the bivouac, and thus all parts of the system 

 are connected. 



The Ecifon raid travels on scent trails made by the ants them- 

 selves — the basis of orientation in all Eciton raiding. The existence 

 of a chemical trail on the path followed by every column may be 



