1983] 
Pesacio & A I Iowa y — Harpagoxenus aniericanus 
157 
aniericanus workers, 54 L. longispinosus slaves and 53 L. ambiguus 
slaves. The average distance between H. aniericanus nests in nest 
groups apparently comprising a single colony was 43.5 cm, with a 
range of 1 1 to 159 cm. The average distance between H. aniericanus 
nests among which there were aggressive interactions was 61.36 cm, 
with a range of 19 to 180 cm. 
In the H. aniericanus nests, L. longispinosus slaves outnumbered 
L. ambiguus slaves by a ratio of almost 4:1, the total number of 
slaves being 803 (79.5%) for L. longispinosus and 207 (20.5%) for L. 
ambiguus. All the H. americanus colonies contained L. longispino- 
sus slaves, and 9 colonies contained slaves of both species. However, 
none of the H. americanus colonies used in this study had only L. 
ambiguus slaves, although such colonies are occasionally found in 
the Toronto region (Alloway unpublished data). Nevertheless, 7 of 
the quadrants studied contained no nests of free-living L. longispino- 
sus, and one of the quadrants in which there were L. ambiguus 
slaves contained no nests of free-living L. ambiguus (see Table 1). 
Unenslaved nests of L. longispinosus were on average somewhat 
more populous than the unenslaved nests of L. ambiguus, the mean 
number of workers per nest being 25.6 for L. longispinosus and 16.8 
for L. ambiguus. 
Discussion 
Our observations indicate that many Harpagoxenus americanus 
colonies are polydomus. This conclusion is based primarily on 
observations of peaceful interactions and of nest fusion among nests 
collected close together in nature, contrasted with observations that 
ants from different H. americanus nests do not always interact 
peacefully. The fighting and raiding observed indicate that H. ameri- 
canus does not possess a unicolonial population structure. Thus, 
peaceful exchange of nestmates and nest fusions, when they occur, 
signify the existence of polydomous colonies. However, polydomy 
in H. americanus is not obligatory. New colonies are monodomous, 
becoming polydomous as they grow. Finally, our observations of 
partial fusions suggest that nests in polydomus colonies may gradu- 
ally become autonomous, perhaps due to cessation of regular con- 
tact between nests. Under these circumstances, new queenless 
“secondary colonies,” similar to those envisaged by Wesson (1939), 
could be formed. 
