390 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



Another characteristic accompaniment of the swarm raid is the loud 

 and variable buzzing of the scattered crowd of flies of various species, 

 some types hovering, circling, or darting just ahead of the advancing 

 fringe of the swarm, others over the swarm itself or over the fan of 

 columns behind. To the general hum are added irregular short notes 

 of higher pitch as individuals or small groups of flies swoop down 

 suddenly here and there upon some probable victim of the ants which 

 has suddenly burst into view. These flies cannot be feeding to any 

 extent, for they rise again instantly. Very probably they are ovi- 

 positing on the prey, with their eggs subsequently carried along 

 incidentally into the bivouac where those unconsumed with the booty 

 may develop along with the Eciton brood. Now and then, in a labora- 

 tory nest containing hurchelli workers and larvae, I have observed 

 maggots that may be the young of these flies. It is probable that 

 their entire life cycle is intimately intermeshed with that of the 

 Eciton. 



No part of the more prosaic clatter, but impressive solo effects, are 

 the occasional calls of antbirds. One first catches from a distance the 

 beautiful crescendo of the bicolored antbird, then closer to the scene 

 of action the characteristic low twittering notes of the antwren and 

 other common frequenters of the raid. For locating swarm raids 

 these are most useful clues as a rule, since the birds ordinarily are to 

 be heard at or near the scene of action from the time of first morning 

 light when the raid begins. However, the calls are not an infallible 

 clue to the raids by any means, for in the respective mating seasons of 

 the different species, they may be heard almost anywhere in the forest 

 except around the Eciton swarm raid. In collaboration with our 

 investigation of 1948, Dr. Kobert Jolmson carried out an intensive 

 behavior study of the antbirds attending hurcheTli swarms (John- 

 son, 1954) . The birds do not feed upon the ants except accidentally — 

 rather they feed on the flushed-out insects which are snatched up by 

 them in quick flight from nearby perches. In between these captures 

 the birds utter a characteristic call. Their music and actions are an 

 inseparable part of this forest phenomenon. 



Burchelli raids have the characteristic form represented by an ex- 

 ample in figure 2. In the morning, from shortly after its beginning 

 at dawn, the size of the mass increases through a steady stream of 

 recruits from the bivouac entering along the consolidation trail 

 through the fan of columns to the swarm. By midmorning (in the 

 nomadic phase), with the swarm perhaps 90 meters or more from 

 the bivouac and more than 15 meters wide, outgoing traffic has de- 

 creased and the principal trail is dominated by a thick procession of 

 returning ants, mainly booty-laden, moving toward the bivouac. The 

 haul — forest invertebrates of many descriptions, fragments of arthro- 



