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Psyche 
[Vol. 85 
experimental arenas containing an arbitrarily selected host-species 
target nest. Under these circumstances, H. americanus raids begin 
when one or more slave-maker workers leave the parasite nest to 
explore the arena. Whenever such a “scout” discovers the entrance 
to the target nest, it returns to its own nest and recruits a raiding 
party. After dispersing the adult residents of the target nest, the 
raiders carry the captured brood back to the slave-maker nest 
(Alloway 1979). 
Recently, it was discovered that H. americanus, L. amhiguus, L. 
longispinosus and probably L. curvispinosus form facultatively 
polydomous colonies (Alloway ef al. 1982; Del Rio Pesado & Allo- 
way 1983). Colonies of the three host species are also facultatively 
polygynous (Alloway c/ 1982). However, H. americanus co\on\ts 
apparently never contain more than one inseminated egg-laying 
queen (Buschinger & Alloway 1977). 
In the present paper, we augment previous findings by presenting 
behavioral observations of H. americanus and its slaves interacting 
with ants from other H. americanus colonies and from unenslaved 
host-species colonies. These observations supplement previous find- 
ings for three reasons: 
1. The interactions observed were among ants from colonies col- 
lected adjacent to one another in nature. 
2. The ants were observed for several weeks. 
3. Ants from small and “weak”, as well as populous and “strong”, 
H. americanus and host-species colonies were observed. 
Materials and Methods 
Nests of H. americanus, L. amhiguus, and L. longispinosus were 
collected on the Erindale Campus of the University of Toronto, in 
Mississauga, Ontario. Since we wanted to observe the behavior of 
ants from parasite nests occurring close together in nature, we 
looked for places where there were at least two H. americanus nests 
within less than 2 m of each other. Whenever such a spot was found, 
we laid out a 2 m by 2 m quadrant centering on the parasite nests 
and then collected, numbered, and mapped the location of all H. 
americanus and host-species nests in the quadrant. Altogether, 19 
quandrants were collected; but two pairs of adjacent quadrants were 
combined to permit observation of large groups of H. americanus 
