266 
Psyche 
[Vol. 94 
Table 1. Comparison of slave-raid frequency with and without removal of scouts 
Date 
No. of Scouts 
Scouts Removed 
Slave Raid 
7/02 
8 
+ 
- 
7/05 
7 
+ 
- 
7/06 
3 
+ 
- 
7/09 
1 
+ 
- 
7/10 
5 
+ 
- 
7/11 
1 
+ 
- 
7/12 
15 
+ 
+ 
7/13 
24 
+ 
- 
7/15 
21 
+ 
- 
7/17 
13 
+ 
- 
7/20 
16 
+ 
+ 
7/21 
- 
+ 
7/22 
- 
+ 
7/23 
- 
+ 
7/24 
- 
+ 
7/25 
- 
++ 
7/27 
- 
- 
7/28 
- 
+ 
7/29 
- 
- 
7/30 
- 
+ 
7/31 
- - 
- 
8/01 
- 
+ 
8/04 
- 
+ 
++ denotes two raids on same day 
Discussion 
Polyergus breviceps is similar to other obligatory parasites in that 
workers do not search for food. Nevertheless, the location of target 
nests by scouts can be thought of as indirect foraging, because much 
of the raided Formica brood is fed to the Polyergus workers and 
queen by their resident slaves. It is therefore not surprising that the 
searching pattern of Polyergus scouts illustrated in Figure 1 is 
almost identical to that described for the ant Cat agly phis bicolor, 
which forages alone for dead arthropods (Harkness and Maroudas 
1985). In this desert-dwelling species, foragers also move away from 
the nest in a linear path, followed by random searching throughout 
a particular sector. Cataglyphis can measure angular directions 
from the pattern of polarized light (Wehner and Menzel 1969), so it 
could forage in a straight line until it found food, and then return to 
