262 
Psyche 
[Vol. 94 
Formica schaufussi nests that were scouted on the same day. And in 
a preliminary field study, the removal of scouts on each of 3 days in 
the field resulted in the absence of slave raids. 
In this paper we report the results of longitudinal field studies on 
two colonies of the western slave-making ant Polyergus breviceps. 
In the first study, we discovered that scouts use a biphasic search 
strategy, consisting of an initial linear component, followed by 
random search within a limited sector. An additional finding was 
that scouts may use three different routes on the outbound run, 
return trip, and slave raid respectively. In the second study, in which 
we removed all scouts during a period of 19 days, we verified their 
importance for raid onset. 
Path of Scout 
Materials and methods 
All studies on scouts were conducted at the Southwestern 
Research Station, located 5 km west of Portal, Arizona. At an 
altitude of 1646 m, the ground in this habitat is covered with bunch 
grass and contains extensive leaf litter from alligator juniper, 
Arizona oak, and Chihuahua pine. The period for this study was 
July 10-30, 1986. To facilitate the detection of Polyergus breviceps 
scouts, one colony was enclosed by a circular, aluminum-flashing 
fence (15 cm high), using the Polyergus nest entrance as the center. 
The radius of the enclosure was 7 m, which insured that all ants 
reaching the fence were scouts (and not the circlers, which routinely 
emerge and mill around the nest entrance prior to raiding). To 
enable scouts to move in and out of the enclosure, the fence 
contained four gaps (15 cm wide) at 90-degree intervals, starting at 
the north end. Beginning at 1400 hr (MST), one person walked 
continuously around the circular fence. Scouts reaching the fence 
usually ran along the inside wall, and left the enclosure immediately 
upon encountering the nearest gap. Sometimes, a scout ran back 
and forth along the same small section of the fence’s inner wall. On 
these occasions, a garden trowel was placed in the scout’s path. When 
the scout moved onto the trowel, it was lifted and placed on the 
ground on the outer side of the fence. The path of each scout was 
marked by placing the stick end of cotton swabs (painted yellow and 
numbered sequentially) into the ground behind the scout, at 
approximately 1-m intervals. Because of the grass and leaf litter, this 
