No. 417.] NESTS OF AMERICAN ANTS. 705 
sickle-shaped mandibles, the cutting edges of which are fur- 
nished with minute serrate teeth. Such mandibles are beauti- 
fully adapted to fighting, but scarcely fitted for the many other 
uses to which these organs are put by most ants.  Polyergus is 
therefore a warrior, and on this account its life presents two 
very different phases, one replete with the brilliant tactics 
whereby it gains possession of the larvae and cocoons of its 
Fic. 15. — a., Polyergus rufescens Latr., subsp. dreviceps Emery, worker ; $., mandible of same ; 
c., Formica fusca L., var. subsericea Say, subvar.; d., mandible of same. 
Slaves, the other characterized by abject helplessness and com- 
plete dependence on these same auxiliaries. - 
The auxiliaries of Polyergus are furnished by the very same 
Species as in the case of F. sanguinea. In this case, also, 
F. fusca is most often victimized, zufibarbis less frequently. 
Occasionally, too, both species are found in the same nest. 
he number of slaves, however, is much greater than in san- 
guinea nests, being about seven-eighths of the entire colony. 
The dulotic expeditions of Polyergus have been often observed 
