ARMY ANTS — SCHNEIRLA 381 



The German term "Wanderameisen" emphasizes the roaming life 

 which the ecitons lead. The branching columns of species like Eciton 

 (E.) hanmtum and Eciton (H.) crassicome and the swarm or column 

 of Eciton (E.) burcheUi and Eciton {Labidus) yraedator are fre- 

 quently encomitered in the forests of the Island, and one may be sure 

 the ants issue from a temporary colony "bivouac" somewhere in the 

 general vicinity. But finding colony headquarters is never an easy 

 matter. Without observing the correct clues one may follow the 

 column in the wrong direction, away from the home site, a mistake 

 easily made in the afternoon particularly. Even if by dint of sharp 

 eyesight, some agility, and some luck we are able to follow the column 

 in the correct direction, it is possible mider certain conditions to 

 pass the actual bivouac without noting any signs of its presence. 

 The ordinary task of column-following is made interestingly more 

 difficult by the fact that each species — the golden-yellow haniatum^ 

 the darkish-brown 'burcheUi^ the reddish-black praedator^ and others — 

 in its own way is color-camouflaged and merges readily with ground 

 colors in the typically dim light of the forest. The course usually 

 is a rough one: through tangled masses of vines with prickly palms 

 as occasional hazards, wild pineapple thickets and a variety of natural 

 mazes formed around fallen trees, up and down steep ravine banks 

 and across elevated bridges formed by lianas, the army ants go readily 

 but not always the human investigator. The main center of raiding 

 and hence the base columns run most frequently through the heaviest 

 growth. There the living prey is most plentiful, and so it is there 

 the advance raiders turn most readily in response to movement and 

 odors from their insect booty, and it is there the human investigator 

 must go if he would follow them. 



We find Eciton colonies by hiking the trails to intersect the raiding 

 lines, then by tracking down the colony base by following the columns. 

 This means that the trail system of the Island has been an indispen- 

 sable asset to searching for and studying Eciton colonies in a system- 

 atic way. Almost without exception even our short-term studies of 

 ecitons must begin with the bivouac, and almost the only way to find 

 this home site is to follow in the raiding columns. In other parts of the 

 Tropics, where trails and roads tend to run outside the forest by human 

 preference, one follows the stream beds in survey work, and the going 

 is considerably slower. In a one-man investigation of 6 months on the 

 Island in the dry season of 1946 (Schneirla, 1949), I worked with 

 30 colonies of hamatum and nearly 20 of hurchelli^ studying two 

 colonies continuously for more than 4 months, and other colonies 

 over shorter intervals— a schedule hardly feasible in a forest other 

 than that of Barro Colorado Island lacking a central system of trails. 

 The techniques of finding and working with army ants depend upon 

 these basic paths first of all. 



