The Role of Scouting in Slave Raids by Polyergus Breviceps (Hymenoptera: Formicidae)

The formicine ant genus Polyergus contains four species, all of which are obligatory social parasites of the related genus Formica. Slave ants are obtained during group raids, in which a swarm of Polyergus workers penetrates a nest of Formica, disperses the adult workers and queen, and carries off the pupal brood (Topoff et al. 1984, 1985). Although many of these pupae are subsequently consumed in the slave-maker's nest (Kwait and Topoff 1984), a significant portion of the Formica brood is reared through pupal development. Workers eclosing from this pupal population subsequently perform their typical functions (i-e., foraging, feeding, nest defense) as permanent members of a mixed-species nest. Ever since the pioneering studies on Polyergus rufescens by Huber (1810) and Emery (1908), on P. lucidus by Talbot (1967) and Harman (1968), and on P. breviceps by Wheeler (1916), it has been well known that slave-making raids are usually initiated by a small group of workers called scouts. These individuals locate target colonies of Formica, return to their colony of origin, recruit nestmates, and lead the raiders back to the Formica nest. Despite the generalization that Polyergus slave raids are typically preceded by scouting, virtually no field studies exist showing the actual paths travelled by scouts, or their overall importance in initiating slave raids. In their study of laboratory colonies of P. lucidus, Kwait and Topoff (1984) found that most raids were indeed directed towards