360 
Psyche 
[December 
Discussion 
It is clear that the absence of callow army ants from raiding 
trails during the first few days of the nomadic phase can not be ex- 
plained on the basis of their inability to follow the chemical trail of 
their colony. Nevertheless, there are significant differences in trail- 
following performance between callow and mature adult ants, espe- 
cially in their speed of running along the trail. If the callows did 
attempt to participate in raiding activities, their deficit in locomotory 
ability could make them very inefficient predators. This, together 
with the observation that callow army ants placed in raiding columns 
are behaviorally disorganized (Schneirla, 1971) makes it likely that 
it is adaptive to the colony for the callows not to participate in raid- 
ing until they have matured. However, the fact that the behavior 
of the callows is adaptive to the colony still does not explain the 
mechanism that keeps them inside of the nest. 
Although there is relatively little data on the behavior of the cal- 
low workers in the nest immediately after their eclosion, Schneirla 
(1952) reported that they feed voraciously. Rettenmeyer (1963) 
also observed callows feeding on booty, but pointed out the difficulty 
of estimating the quantity of food consumed or the duration of the 
active feeding periods. If the callows are preoccupied in feeding 
intensively during the first few days after their emergence from the 
pupal stage of development, this could account for their absence 
from raiding columns. 
Another hypothesis stems from the observation that callow workers 
tend to cluster tightly together, both in the bivouac and in emigra- 
tion columns (Rettenmeyer, 1963; Schneirla, 1938). This intense 
clustering may result from an extreme sensitivity of the callows to 
chemical and tactual stimuli. Inside the bivouac the intensity of 
tactual stimulation is high, as a result of the continual contact among 
callows and other ants. The nest is also saturated with trail sub- 
stance and other chemical stimuli (which arise from the workers, 
the queen, and even the booty). Accordingly, whenever a callow 
leaves the bivouac the intensity of stimuli impinging upon it decreases 
abruptly. Outside the nest the amount of tactual stimulation is de- 
creased as the adult ants fan out along the trail. The intensity of 
chemical stimuli is also decreased, as volatile chemicals diffuse and 
as the concentration of trail chemicals decreases from a dense sphere 
surrounding the ants inside the nest to only a narrow trail leading 
away from the nest. As a result, callows attempting to leave the 
nest would experience a sudden decrease in chemotactual stimulation, 
with the result that they would become disoriented. This, in turn, 
