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Psyche 
[September-December 
planation of our observations that (a) workers and queens are pro- 
duced most abundantly in “branch colonies” which possess no fully 
functional egg-laying worker at all and (b) “branch colonies” that 
possess one or more egg-laying workers produce only or preferably 
males. 
The functional significance of “branch colonies” in H. americanus 
remains uncertain. As Wesson (1939) demonstrated experimentally, 
they do not result from mere mechanical crowding in the “primary 
colonies.” Moreover, our observations confirm those of previous 
investigators in indicating that queenright americanus colonies tend 
to be quite small, The branch colonies do serve as a source of 
surplus males which might be essential to insure the insemination 
of all americanus queens. However, this possibility seems unlikely 
since “primary colonies” produce large numbers of males and since 
both H. canadensis and H. sublaevis appear to get along without 
“branch colonies.” Indeed, since “branch colonies” often occur 
within less than a meter of queenright colonies from which they 
may well have arisen, it is hard to understand why raiding compe- 
tition between a “primary colony” and its “branches” would not 
interfere with “primary colony’s” capacity to exploit host-species 
resources. However, such competition might be minimized by the 
fact that americanus raiders kill very few host-species adults in their 
raids and the tendency of americanus colonies to rear host-species 
queens and males in their nests and then apparently to permit these 
individuals to go out on nuptial flights (Alloway, in press). These 
relatively nondestructive characteristics may permit dense ameri- 
canus populations to survive without depleting host-species re- 
sources. 
However, perhaps the best hypothesis regarding a possible adap- 
tive advantage for the “branch colony” system in americanus arises 
if we suppose that the raiding range of each americanus nest is quite 
restricted. Thus, the formation of “branch colonies” at the periph- 
ery of the range of a “primary colony” may greatly expand the 
range of action of a “primary colony” and its “branches.” 
However, these interpretations are highly speculative. Further 
detailed field work is needed to work out the spatial relationship 
between americanus “primary colonies” and their “branches.” In 
addition, a combined set of laboratory and field studies is needed 
to determine the means by which branch colonies are formed and 
