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[Vol. 90 
e. In quadrant 19, both the slaves and the slave makers from 
different nests fought whenever they met; and the slave makers in 
one nest mounted an incomplete raid against the other slave- 
maker nest. 
These observations indicate that H. americanus is not a unicolo- 
nial species. Aggressive behavioral barriers preventing the exchange 
of nestmates and nest fusion exist between some H. americanus 
nests. This fact strengthens the conclusion that exchange of nest- 
mates and brood and nest fusion, when they do occur, are indicative 
of the existence of a polydomous colony. 
Somewhat peculiar partial fusions were observed in quadrants 7 
and 15. In both quadrants, the slaves peacefully moved into a single 
nest. In quadrant 7, the slave makers from the two nests fought. In 
quadrant 15 where there were 5 H. americanus nests, some of the 
slaves attacked slave makers which had been living in other nests 
prior to the fusion. These partial fusions may represent situations in 
which lack of contact between nests had begun to produce auton- 
omy between nests. 
Once the raiding season was over, we observed the formation of 
secondary nests in quadrants 1 and 6. In both quadrants, some of 
the ants which had been occupying a single nest moved into a 
second nest. In both cases, exchange of nestmates and brood con- 
tinued for two weeks, when observations ended. 
In 7 quadrants, we were unable to find an H. americanus queen, 
despite our efforts to collect each nest completely and to search 
beyond quadrant boundaries for additional slave-maker nests belong- 
ing to these nest groups (see Table 1). However, in each of these 
cases, all the maturing H. americanus adults were males, a fact 
which indicates that these particular nests had not been receiving 
female brood from a primary nest and is consistent with the suppo- 
sition (Buschinger & Alloway 1977) that thelytoky does not occur in 
H. americanus. 
The total number of adults of various species in all nests studied is 
summarized in Table 1. The total number of H. americanus workers 
was 1 15, with the average slave-maker nest containing about 2 H. 
americanus workers. The largest number of slave makers in a single 
nest at the time of the original census was 13; and the largest number 
of nests in a single apparently polydomus H. americanus colony was 
6 in quadrant (9 + 10). Altogether, this colony contained 19 H. 
