152 
Psyche 
[Vol. 88 
goal of the present study was to reduce callow stimulation and 
thereby delay the onset of the nomadic phase, overfeeding com- 
menced late in the statary period. For the first colony, emigrations 
were delayed approximately 6 days. In the second overfed colony, 
we were able to virtually eliminate the nomadic phase, together with 
all associated patterns of raiding and emigration behavior. 
Methods and Procedures 
This study was conducted during July and August, 1980, in a 
desert-grassland habitat, 8 km east of Portal, Arizona. The site was 
chosen because the pavement-like substrate and patchy vegetation 
provided us with an excellent view of the ants’ raiding and 
emigration activities. Surface soil temperatures averaged 50° C at 
1500 hr (MST) and 17° C at 0200 hr throughout the summer 
(Mirenda et al. 1980). As a result of the severe daytime temperatures 
and aridity, colonies of N. nigrescens were usually active on the 
surface only between 1900-0500 hr. 
Colonies were located by walking through the study area with 
gasoline lanterns or miner’s cap lamps. Colony no. 1 was found on 
July 11, at the end of a nomadic phase, and observed nightly 
throughout its next statary period. During the subsequent nomadic 
phase, the colony was estimated to contain approximately 80,000 
adults and 50,000 larvae. Colony no. 2 was collected on July 14, 
during its last nomadic emigration, and maintained in the labora- 
tory (see Topoff et al. 1980b for details of the rearing procedure) 
until the pupal brood was fully pigmented. Prior to release in the 
field, the colony was culled to contain 4,000 adults and 4,000 pupae. 
By the next nomadic phase, approximately 4,500 larvae were also 
present in the colony. This small colony size was chosen for two 
reasons: (1) to increase our ability to appreciably overfeed the 
colony; and (2) a laboratory colony of comparable size had 
previously been released without food supplementation, as part of a 
study designed to show that laboratory rearing and population 
reduction do not alter qualitative aspects of nomadic behavior. This 
colony could therefore serve as a convenient control for our 
artificially-fed colony. 
Food for both experimental colonies consisted of adult and brood 
individuals of the myrmicine ant Novomessor cockerelli, and 
workers of the termite genus Gnathamitermes. To collect Novo- 
