1955] 
Wilson — Formica ivheeleri 
133 
over other adults in this part of the nest and their close 
association with the brood gave the strong impression that 
they were serving as nurses. 
At noon on the next day the wrecked nest was visited 
again. The colony was busily engaged in migrating to the 
undamaged part of the fusca nest which had been raided the 
day before. The fusca workers were no longer in evidence 
and presumably had been forced out. The ivheeleri were 
doing all the work in this operation; most of the workers 
in the migrating file were carrying something in their 
mandibles, either brood, or slaves, or other ivheeleri. In 
contrast, many of the slaves were running back and forth 
with the slave-makers but none were burdened. 
In summary, an interspecific division of labor was pro- 
nounced in this particular case. The slave-maker species 
ivheeleri functioned in raiding, nest defense, and trans- 
port during colony migration. Workers of the slave species 
neorufibarbis accompanied the ivheeleri on their raid and 
helped them excavate one of the besieged nests when the 
entrance holes were blocked; they were also active in nest 
defense. The fusca workers were very passive, did not 
contribute materially to the slave-raid, and gave every sign 
of serving primarily as nurses and food receptacles. A 
deeper significance of the dulotic habit is underscored 
here. It is apparent that the slave-maker colony not only 
adds to its labor force quantitatively by taking slaves but 
may also incorporate specialists that increase the efficiency 
of the colony in a fashion analogous to that seen in normal 
worker polymorphism. 
Literature Cited 
Creighton, W. S. 
1950. The ants of North America. Bull. Mus. Comp. Zool. Harv., 
104: 1-585, 57 pis. 
Forel, A. 
1929. The social world of ants. English translation by C. K. Ogden. 
Albert and Charles Boni, New York. Two volumes. 
Talbot, M. and C. Kennedy. 
1940. The slave-making ant, Formica sanguinea subintegra Emery, 
its raids, nuptial flights and nest structure. Ann. Ent. Soc. Amer., 
33: 560-577. 
