Ecology of Raiding Behavior in the Western Slave-Making Ant Polyergus breviceps (Formicidae)

Population characteristics of the western slave-making ant Polyergus breviceps were studied during the summer of 1981, in the Chiricahua Mountains of southeastern Arizona. Slave raids were conducted on colonies of Formica gnava in late afternoon, past the peak in diurnal temperature. During the mating season, few to several hundred winged queens might accompany the slave-raid swarm. The median numbers of Polyergus workers participating in the slave raids were 1,189, 1,784, and 2,234 for the three study colonies, and up to 2,800 Formica pupae might be captured during a single day's raid. Thus colony size and booty capture for P. breviceps were 3-7 times larger than for the closely related eastern species P. lucidus. It is hypothesized that this discrepancy is due to the milder winters in southeastern Arizona, which may lead to increased survivorship and a longer season of brood production.