154 
Psyche 
[Vol. 90 
Results 
There was a total of 19 quadrants. However, quadrant 1 was 
merged with quadrant 2 and quadrant 9 with quadrant 10 when an 
additional H. americanus nest was found in close proximity to a 
group of other H. americanus nests, but outside the original quad- 
rant boundary. Altogether, the quadrants contained 49 H. ameri- 
canus nests, 57 L. ambiguus nests, and 59 L. longispinosus nests (see 
Table 1). 
Our most common observation was “fusion” of all the H. ameri- 
canus nests in a quadrant. By “fusion”, we mean that eventually all 
the ants from two or more H. americanus nests peacefully moved 
into a single nest after exchanging adult nest-mates and brood 
among the different nests for varying lengths of time (Figure 1). This 
exchange was carried out exclusively by slaves. The ability of nests 
to fuse shows that there is no behavioral barrier to interactions and 
exchange of nestmates among nests and thus indicates either that all 
the ants are members of the same polydomous colony or that H. 
americanus is a unicolonial species with no behavioral barriers 
between its nests. Fusion of all the slave-maker nests was observed 
in quadrants (1 + 2), 5, 6, (9 + 10), 11, 12, 13, 16, 17, and 18, in 
which there was never more than one slave-maker queen. 
However, we did not always observe fusion among H. americanus 
nests: 
a. In the control quadrant where two H. americanus nests 
from different collection sites were arbitrarily set up near each 
other, the ants showed no tendency to fuse; and the slave makers 
from one nest successfully raided the other slave-maker nest. 
b. Quadrants 3 and 8 each contained two H. americanus 
queens living in different nests with slaves and a brood. In quad- 
rant 3, there was little behavioral interaction between the ants in 
the two nests. However, in quadrant 8, after the brood matured, 
the H. americanus workers in one nest raided the other slave- 
maker nest. 
c. In quadrant 4, there was little contact between the ants in 
the two H. americanus nests, but the small amount of contact 
observed was hostile. 
d. In quadrant 14, slaves and slave makers in two nests fused 
and then fought with the slaves and slave makers in a third nest. 
