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nests that were scouted on the previous raid day. Our present field 
study with P. breviceps confirms the importance of scouting in the 
natural habitat. Because all scouts collected were returned to their 
nest in late afternoon, the colony’s “interpretation” might have been 
that these scouts were simply unsuccessful in locating a colony of 
Formica. If this were the case, an adaptive colony response would 
be to send out more scouts on successive days. Note (in Table 1) that 
the number of scouts from July 7-July 1 1 ranged between 1 and 8, 
but that 15-25 scouts were collected between July 12 and July 20. It 
is plausible to hypothesize that the magnitude of scouting can be 
varied according to the colony’s requirements, but a more rigorous, 
statistical analysis must await a larger sample size. 
The data from July 12 and 20 also show that raids can be organ- 
ized even when scouting has not taken place for at least one week, 
but we do not know how recruitment takes place when this occurs. 
When groups of Polyergus are led by same-day scouts, the raid 
typically mimics the biphasic nature of scouting. Thus, the raid 
starts with a relatively linear movement away from the nest, during 
which the swarm advances without stopping. This is followed by the 
second phase in which the ants periodically stop advancing, fan out 
in all directions, and search under rocks and leaf litter (Topoff et al. 
1984). It will be interesting in future field studies to observe how 
slave raids proceed when not organized by same-day scouts. Under 
such circumstances, the linear phase of raiding might be eliminated, 
so that the Polyergus swarm is forced to advance in a more deliber- 
ate manner, with more numerous searching stops even close to the 
nest. Finally, formicine ants such as Formica rufa exhibit site alle- 
giance, a process that is based upon individual memory of spatially- 
organized visual cues (Rosengren and Fortelius 1986). Using 
individually-marked Polyergus , we now plan to determine whether 
each scout has a particular compass direction and sector in which it 
regularly searches for Formica colonies. 
Summary 
Slave raids by Polyergus breviceps are initiated by one or more 
scouts which locate target colonies of Formica gnava, and recruit 
nestmates to participate in group raids. Field studies in southeastern 
Arizona showed that scouting comprises two distinct phases. The 
first is a linear movement away from the nest, during which no 
