1983] 
Allow ay & Del Rio Pesado — Harpagoxenus 
433 
ences between populations, may account for differences between the 
present results and those of Wesson (1939). 
A number of our observations pertain to limits on the success of 
slave-raiding in polydomous parasite colonies. Individual H. ameri- 
canus workers can rarely capture brood and are sometimes killed by 
target-colony workers. Yet, groups of 4 or 5 H. americanus workers 
can successfully raid almost any target nest. Thus, H. americanus 
colonies need to deploy their raiders in raiding parties containing 
several parasite workers. However, polydomy sometimes prevents 
such deployment. The slave-makers rely on their slaves to carry 
them from nest to nest in polydomous colonies; and the slaves often 
fail to assemble the slave-makers in a single nest from which success- 
ful raids could be mounted. As a consequence, some polydomous H. 
americanus colonies fail to organize raiding parties containing 
enough slave-makers to capture brood from neighboring host- 
species colonies. 
This difficulty encountered by H. americanus colonies living in 
more than one nest has led us to question the adaptive value of 
polydomy in the slave-maker population studied. Both the Lepto- 
thorax host species enslaved by H. americanus in the Toronto 
region form facultatively polydomous colonies (Alloway et al. 
1982). Thus, if enslaved host-species workers behave like unenslaved 
conspecifics, slaves should tend to provide a polydomous colony 
structure for the parasites. Perhaps, some H. americanus colonies 
are polydomous because of this behavioral propensity of their slaves 
and despite the fact that polydomy is detrimental to efficient 
raiding. 
In addition, polydomy may account for some of the overt aggres- 
sion observed in the present study. By extension, polydomy might 
partly explain the similar forms of slave aggression manifested by 
Leptothorax slaves living in L. duloticus colonies (Wilson 1975). 
Let us imagine that a slave-maker colony divides, with some of 
the parasites and slaves remaining in the original nest, while others 
move to another nest. Let us further suppose that the slave-makers 
in the two nest raid independently. In such a situation, young slaves 
maturing from captured brood in each nest might learn to recognize 
as nestmates only those particular slave-makers with which they 
were living. If the ants from the two nests later reunited, then the old 
slaves might accept all the slave-makers, while the young slaves 
