TRAIL FOLLOWING AND ITS DEVELOPMENT IN 
THE NEOTROPICAL ARMY ANT GENUS ECITON 
(HYMENOPTERA: FORMICIDAE: DORYLINAE) 
By Howard Topoff, Katherine Lawson 
and Patricia Richards 1 
Introduction 
Results of numerous field studies on the neotropical army ants 
Eciton hamatum (Fabricius) and E. burchelli (Westwood) have 
shown that newly eclosed callow workers do not participate in 
adult activities such as raiding until they have matured in the col- 
ony environment for several days after the onset of the nomadic 
phase. Nevertheless, the callows of both species do emigrate along 
with the colony, beginning on the very first nomadic day (Schneirla, 
1971). We have offered several hypotheses to account for the be- 
havioral deficit of the callows. One hypothesis proposes that the 
sensitivity of the callows to their colony’s chemical trail is too low 
for them to be able to follow along it during the day’s raid. By 
late afternoon, however, the strength of the trail may be sufficiently 
increased (as it is constantly reinforced by tens of thousands of ants 
running back and forth over it) so that the callows are able to par- 
ticipate in the emigration. This paper presents the results of a study 
designed to compare the performance of callow and mature adult 
workers of E. hamatum and E. burchelli on their own colony’s trail. 
Methods 
This study was conducted on Barro Colorado Island, Panama 
Canal Zone. Features of the Island that make it suitable for army 
ant research have been described by Rettenmeyer ( 1963). 
Field methods consisted of daily patrols of the Island’s numerous 
trails to locate statary colonies. The first indication that a colony 
was about to enter a new nomadic phase was the appearance of empty 
pupal cases on the ground near the bivouac, and the presence of 
lightly-pigmented callow workers inside of the nest. The first nomad- 
ic day was defined as the day on which the first emigration of the 
entire colony took place. 
Callow and mature adult ants were collected by collapsing a sec- 
department of Psychology, Hunter College of the City University of 
New York, and Department of Animal Behavior, The American Museum 
of Natural History, New York, N.Y. 10024. 
Manuscript received by the editor November 20, 1972 
357 
