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[Vol. 85 
place where they could safely deposit any brood with which they 
had escaped, the workers returned to the invaded nest and carried 
off more brood. The slave-makers countered all these efforts by 
guarding the nest entrance (Alloway 1979) and by charging and 
snapping at target-nest workers. 
Alloway (1979) observed that target-nest workers always fled with 
whatever brood they might manage to carry almost immediately 
after the arrival of a raiding party. In these circumstances, the slave- 
makers did not use their large, specialized mandibles against the 
residents of target nests. In the present study, a broader range of 
target-nest resistance and slave-maker aggression were observed. 
The workers in some target nests fled very shortly after the raiders 
arrived; and, in these cases, the slave-makers injured very few, if 
any, target-nest residents. However, in other target nests, the 
workers bit and stung the invaders. The slave-makers crushed such 
resistance by employing their large mandibles to dismember their 
adversaries. Slaves in raiding parties also attacked target-colony 
workers, but it was apparent that the success of the always outnum- 
bered raiders depended mainly upon the activities of the slave- 
makers. 
After all the adults had been killed or driven from the target nest, 
the raiders transported the captured brood to the slave-maker nest. 
Most brood was carried by slave-makers, although slaves sometimes 
carried one or two larvae or pupae. Brood transport generally lasted 
only a few hours, after which the raiding party vacated the target 
nest. Only one H. americanus colony manifested the phenomenon 
reported by Wesson (1939) of raiders requiring 2 or 3 days to com- 
plete brood transport. After the raiding party had abandoned the 
target nest, its previous inhabitants often returned. 
Other Behavior 
Our observations confirm that Leptothorax slaves do most of the 
work in H. americanus colonies. The slaves forage for food, feed 
and groom the parasite adults and brood, and defend the area 
around H. americanus colonies by attacking foraging workers from 
neighboring Leptothorax colonies whenever they are encountered 
near an H. americanus nest. The slave-makers do none of these 
things on a regular basis. Indeed, the parasites appear never to leave 
their nests except to scout {i.e. to “look for” target nests). Since 
scouting slave-makers invariably return to the same nest from which 
they departed, the parasites are even dependent on their slaves to 
