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[Vol. 92 
Figure 2. Pleometrosis in V. perganciei natal nests collected at South Mountain 
Park March 1983. 
Among other primary pleometrotic ant species, queen density is 
correlated with average number of cofoundresses/ nest (M. mimicus: 
Bartz and Holldobler 1982; Solenopsis invicta: Tschinkel and 
Howard 1983). Queens seem predisposed to cofound and readily 
join conspecific queens when encountered. Under high queen 
density the probability of such encounter is high, insuring pleome- 
trosis. High queen densities are common in M. mimicus and S. 
invicta , for adult colonies release alates synchronously during the 
flight season. Adult V. pergandei colonies, however, release alates 
(often asynchronously; Fig. 1) over a lengthy period. In 1984 queen 
density after any flight was low; pleometrosis was nonetheless 
common. Queens seemed attracted to sites relatively protected from 
predators, e.g., under flat rocks or boards, rather than avoidant of 
adult conspecific colonies. We believe V. pergandei’s flight season 
precludes pleometrosis through random association under high 
queen density. 
Although the exact mechanism generating pleometrosis remains 
unclear, we have evidence that V. pergandeis mating system is 
