1955] 
Wilson — Formica tvheeleri 
131 
a clearcut interspecific division of labor. The complex 
organization of this colony was so interesting in every 
detail that I have considered it worthwhile to record below 
all of my observations, despite the fact that they pertain 
to a single and possibly aberrant case. 
The mixed colony was first encountered at 2 :30 on a 
warm, sunny afternoon, July 20, 1952, in a meadow near 
Madison Junction, Yellowstone Park, Wyoming (elevation 
6800 feet). The tvheeleri workers, accompanied by large 
numbers of neorufibarbis and a very few fusca, were in 
the process of raiding two nests simultaneously, one of 
fusca about eighteen feet from the home nest, and another 
of lasioides about seven feet beyond in a straight line. 
The exteriors of both raided nests were inconspicuous, 
each consisting of nothing more than several entrance 
holes in the open ground. The tvheeleri-neorufibarbis 
raiding file contained workers spaced at intervals averag- 
ing about six to eight feet. Most were halting at the fusca 
nest, but some were bypassing it and proceeding on to the 
smaller lasioides nest. The scene around the raided nests 
was one of outstanding confusion. Frenzied fusca and 
lasioides, some carrying brood, were mingled with the 
tvheeleri and neorufibarbis slaves. Running over the same 
spot were fusca and neorufibarbis from alien nests, pos- 
sibly drawn to the scene by the general excitement. Need- 
less to say it was difficult at any given time to pick out 
the slaves, the ants being raided, and the extraneous 
marauders. 
Many of the homeward bound tvheeleri were transport- 
ing pupae, neorufibarbis slaves, and other tvheeleri. The 
neorufibarbis were never laden and seemed to be running 
back and forth without contributing any service to the 
raid. On a single occasion a fusca slave was observed 
carrying one of its tvheeleri mistresses. The method of 
adult transport was the same as that already described in 
the literature for other Formica: the ant to be carried 
was approached face-to-face, seized by the mandibles, and 
lifted aloft; it submissively curled its body under the head 
of its transporter, folded in its legs, and became completely 
still. 
