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[Vol. 85 
host-species nests ranged from 0 to 17. This variablity in nest density 
is probably correlated with small-scale differences in the availability 
and suitability of natural nest sites. In addition, the history of slav- 
ery in a particular spot might affect nest density, since H. american- 
us colonies may destroy or drive away adjacent host-species 
colonies. 
Another kind of demographic variability involved the number of 
nests occupied by single colonies. Some H. americanus and some 
host-species colonies were initially polydomous. In the laboratory, 
some initially polydomous colonies moved into a single nest 
(became monodomous) before any significant interactions with 
members of other colonies occurred; but others remained polydom- 
ous during behavioral interactions with ants from other colonies 
(Del Rio Pesado & Alloway 1983). To raid host-species nests suc- 
cessfully, H. americanus colonies must deploy raiding parties con- 
taining several H. americanus workers. In successful polydomous 
H. americanus colonies, the slaves made this possible by carrying all 
or almost all the parasite workers to a single nest before raiding 
began. While so doing, the slaves sometimes (but not always) moved 
the entire H. americanus colony into one nest. In other polydomous 
slave-maker colonies where the slaves failed to assemble the parasite 
workers in this way, many slave-makers were killed during uncoor- 
dinated attacks on target nests. 
A third kind of demographic variability involved differing degrees 
of maturity among slave-maker colonies. When collected, some of 
our H. americanus colonies were incipient {i.e. initially contained 
only an H. americanus queen, some slaves, and a brood), while 
others already possessed slave-maker workers. Wesson (1939), study- 
ing ants from the east-central United States, found that H. ameri- 
canus began to raid only after the overwintered H. americanus 
brood had matured. In contrast, overwintered parasite workers in 
our colonies from southern Ontario began to raid before all their 
overwintered brood had matured. As young H. americanus workers 
eclosed, they augmented the raiding forces of mature colonies and 
initiated raiding in incipient colonies. Thus, mature colonies could 
start raiding earlier and had the potential to raid longer than incip- 
ient colonies. In both incipient and mature colonies, first-year H. 
americanus workers were involved in all phases of raiding {i.e. 
scouting, attacking target nests, and transporting captured brood). 
