1981] Topoff, Rothstein, Pujdak, & Dahlstrom — Army Ants 155 
colony to begin raiding earlier than usual. Thus, although we 
arrived at the site by 1800 hr, a long (60 m) emigration was already 
in progress. Given the large size of the colony, we decided to 
terminate food-augmentation. The colony remained nomadic for 
the next nine days, during which time it emigrated on six nights. 
In order to determine whether we had been successful in delaying 
the onset of the nomadic phase, three independent types of evidence 
were analyzed: (1) phase length: (2) callow pigmentation; and (3) 
larval size. Collectively, our data indicate that the nomadic phase 
was indeed delayed for 4-8 days. 
Phase Length: Because the colony was temporally anchored, July 
13 can be considered the first statary day, August 5 the first nomadic 
day. Thus, the statary interval becomes 23 days (Table 1). Accord- 
ing to Mirenda and Topoff (1980), the range of statary-phase 
duration for N. nigrescens in the same study area is 15-19 days, with 
a modal length of 16 days. This suggests that the minimum delay in 
nomadic onset for our colony was 4 days. If we use instead Mirenda 
and Topoffs modal duration, the delay is calculated as 7 days. 
Callow pigmentation: Newly eclosed callows of N. nigrescens are 
yellow and acquire adult-like pigmentation between 7-12 days. 
Several hundred callows were collected from the colony during its 
first emigration on August 5, and compared with preserved samples 
collected daily from nomadic colonies in previous years. Although 
this form of visual comparison can not always pinpoint the exact 
post-eclosion day, callows from the artificially-fed colony were 
substantially more pigmented than those typically collected from 
other colonies on the first nomadic night. Our comparison between 
these callows and previously preserved specimens indicated a post- 
eclosion age of between 5-8 days. 
Larval size: Several hundred larvae were collected by aspiration 
from the first emigration. By visual inspection, we separated the 10 
largest and 10 smallest larvae and measured them with the aid of a 
dissecting microscope fitted with an ocular micrometer. The mean 
length of the large group was 4.0 mm (range = 3. 8-4. 2 mm), as 
compared with a mean of 1.5 mm (range = 1.3- 1.7 mm) for the 
small group. When these data are compared with Mirenda and 
Topoffs (1980) graph of larval growth versus nomadic day, they 
correspond to a range of nomadic days between 4-6. 
The nightly patterns of activity for colony no. 2 and for the 
control colony are summarized in Table 2. For this small colony, we 
