1959] 
Wilson — Tandem running 
31 
foraging that involves, in most cases, only two workers at a time. 
The leader moves outward from the nest, with a single follower close 
behind. The communication is as follows: the leader remains perfectly 
still until touched on the abdomen by the follower ant. Then it runs 
forward for a distance of approximately 3 to 10 mm (or one to 
several times its own body length), only to come to a complete halt 
again. The follower ant is in a highly excited state, apparently stimu- 
lated by a secretion released by the leader; other workers approaching 
the leader become similarly excited, even when the latter is com- 
pletely immobile at the time. After each contact and subsequent 
“drive” of the leader forward, the follower may press immediately 
behind and drive it again. More commonly, it circles widely about 
in a hurried movement that usually lasts for several seconds and may 
take it as far as a centimeter from the path set by the leader. In 
short time, however, the circling brings the follower once again into 
contact with the leader. If it touches the leader on the head or from 
the side, the latter does not move. In such cases the follower invari- 
ably moves around to the rear of the leader, touches it on the abdomen 
and starts it forward again. 
On th ree occasions, the author removed the follower worker with 
a pair of forceps and lightly touched the leader on the abdomen with 
a fine vegetable fiber or human hair in an attempt to drive it artificial- 
ly. The attempts were only partly successful, perhaps because the 
stimulus was too crude. In each case the leader moved forward, 
stopped, was touched again, moved forward, stopped, was touched a 
third time, and continued running thereafter. The runs between 
stimuli were somewhat longer than under natural conditions. The 
workers were successfully driven in this way only for distances of 
several centimeters before breaking away. In an attempt to induce 
following artificially, various body parts of workers were crushed on 
to the tips of strips of paper, which were then offered to workers 
around the nest entrance. Workers were both excited and mildly 
attracted, in contrast to a neutral or flight reaction to untreated strips, 
but they could not be induced to follow when the strips were drawn 
slowly over the ground. 
In the great majority of cases, tandem running involved only two 
workers. Occasionally a third worker crowded in closely behind the 
leader worker but did not continue following for more than a few 
centimeters. Additional workers became excited by the leader only 
when they encountered it directly. There was no evidence of any 
kind of an odor trail. 
