1983] 
Allow ay & Del Rio Pesado — Harpagoxenus 
429 
In this last respect, H. americanus apparently differs from the Euro- 
pean H. suhlaevis (Nylander), in which slave-makers in mature col- 
onies do not begin to scout until their second year (Buschinger et a/. 
1980). We also observed an apparent effect of experience on scout- 
ing. On their first forays in the spring or after eclosion, scouts 
ventured only a short distance from their nest. The distance trav- 
elled became greater as the number of forays increased. 
Alloway ( 1 979) observed that H. americanus workers could scout 
either singly or in small groups. In the present study, only individual 
scouting was observed. Alloway (1979) also observed that, whenever 
a lone scout discovered the entrance to a target nest, it would return 
to its own nest and recruit a raiding party. However, in the present 
study, lone scouts sometimes attacked target nests by themselves. 
Nevertheless, lone H. americanus workers rarely, if ever, captured 
any brood. Invasion of a target nest by a single slave-maker excited 
the target-colony workers and often caused them to attack the 
intruder. Some lone intruders were killed. 
The success of raider recruitment was highly variable. Upon 
entering its nest, a scout that had discovered the entrance to a target 
nest was immediately surrounded by a cluster of slave-makers and 
slaves. Shortly thereafter, the scout would make its way back to the 
nest entrance and leave. That the slave-maker was now almost cer- 
tainly laying down a pheromone trail was indicated by the fact that 
it conspicuously dragged its gaster along the substrate while being 
closely followed by a column of other slave-makers and/or slaves. 
All scouts that had located target nests excited their nestmates; and 
most initiated processions. The variable success of raider recruit- 
ment seemed to depend on the “steadiness” of the recruiter’s move- 
ment and orientation while leading the procession. Successful 
recruiters moved steadily forward without making any abrupt turns. 
Less successful recruiters stopped for prolonged periods and 
changed direction abruptly. Such hesitation caused nestmates to 
leave the procession; and badly disoriented scouts lost all their fol- 
lowers. Some initially unsuccessful individuals later relocated the 
target nest and went back to their nest to try again. 
The arrival of a raiding party containing several H. americanus 
workers and (often) a number of slaves always caused “alarm” in the 
target nest. Workers and queens would snatch up larvae and pupae 
and make frenzied efforts to leave the nest. Whenever they found a 
