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accepted only familiar individuals. This scenario could explain our 
observations of slaves biting and dragging slave-makers out of nests. 
The aggression observed was always an individual matter. Some 
slaves accepted all the slave-makers, while other slaves accepted 
certain slave-makers and attacked others. 
A somewhat similar hypothesis might account for the imperfect 
behavioral boundaries between some incipient H. americanus colo- 
nies and nearby unparasitized nests. An H. americanus queen founds 
a new colony by entering a host-species nest, killing or driving off 
the adults, and capturing worker pupae that subsequently mature to 
become her first slaves (Wesson 1939; Sturtevant 1927). If a parasite 
queen founded a colony in one nest of a polydomous Leptothorax 
colony, it would not be surprising if some of the parasite’s first 
slaves were acceptable in other nests of the same colony. Similarly, 
“free” workers from that colony might be acceptable in the slave- 
maker nest. However, this hypothesis cannot explain how, under 
these circumstances, a parasitized nest could unidirectionally siphon 
brood and workers from an unparasitized nest or how an H. 
americanus queen could become more attractive than a Leptothorax 
queen. Yet, H. americanus queens and the queens of many other 
socially parasitic species somehow usurp the place of host-species 
queens (Wilson 1971). How parasite queens accomplish this feat 
remains an important subject for future research. 
Polydomy also cannot account for the case where slaves cared for 
an H. americanus queen and her brood but killed all eclosing H. 
americanus workers. Explaining this phenomenon would require 
understanding the mechanisms of nestmate recognition in these spe- 
cies; and these mechanisms are incompletely understood. However, 
studies in progress (R.J. Stuart, personal communication) indicate 
that apparent “mistakes” in nestmate recognition are possible in 
these host species and that//, americanus may exploit these possibil- 
ities. When slaves work for a parasite queen, they may be mistak- 
enly identifying her as a nestmate. When the same slaves destroy the 
parasite’s offspring, they may be correctly identifying them as aliens. 
Gladstone (1981) discussed various theoretical reasons why slave 
workers should not “revolt” against slave-makers. However, our 
observations of H. americanus colonies and Wilson’s (1975) obser- 
vations of Leptothorax du/oticus colonies show that individual 
slaves sometimes manifest what might be interpreted as “rebellious 
behavior”. If our inferences about polydomy are correct, whole 
