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[Vol. 95 
than 50% of the workers were fatally wounded. Only the soldier 
made additional contacts following a fatal snap while both the sol- 
dier and the worker participated in encounters if there was no fatal 
snap. Again, soldiers refrained from further snaps during contacts 
after a fatal snap. Soldiers delivered a fatal snap in a mean time (± 
standard error) of 37 ± 7 seconds in a 1.5 cm 2 arena, 51 + 10 
seconds in a 3.0 cm 2 arena, 62 + 8 seconds in a 4.5 cm 2 arena, and 80 
± 13 seconds in a 6.0 cm 2 arena (Fig. 2b). The percentage of soldier 
encounters following a fatal snap decreased as the arena size 
increased and was 66% at 1.5 cm 2 , 58% at 3.0 cm 2 , 53% at 4.5 cm 2 , 
and 37% at 6.0 cm 2 (Fig. 2c). The number of encounters following a 
fatal snap by a soldier was higher at smaller arena sizes since the 
encounter rate was higher and more than 80% of the fatal snaps 
were delivered by the third encounter. The soldier also required 
fewer snaps to deliver a fatal snap as arena size diminished (Figure 
2d). 
Even though the response of a soldier to an alien worker was 
more rapid as arena size decreased, not all workers were killed. 
Some avoided a fatal encounter with a soldier; escape was most 
frequent at the largest arena size (Table 1). In fact, 25% of the 
workers behaved aggressively and attacked a soldier. Aggressive 
workers were usually slashed by the sharp and powerful soldier 
mandibles but a few workers were able to evade the soldier defenses. 
During these encounters the soldier became the victim, having one 
or both antennae removed just above the scape. The behavior of 
workers when confronted with an aggressive soldier was grouped in 
two categories: 1) the worker responded actively (ran away or 
became aggressive), or 2) the worker remained stationary (no 
motion). Each category had a nearly equal probability but more 
workers survived if their behavior was active (Table 2). 
Soldier vs. worker interactions: immobilization of soldiers 
or workers 
Worker behavior toward a soldier and soldier behavior toward a 
worker were distinguished when one of the individuals was immobi- 
lized while the other moved freely. Soldier snaps to the worker 
abdomen were less frequent and less violent than snaps to the 
worker head (Table 3). Workers approached the abdomen of an 
immobilized soldier, made brief touches with the antennae and 
retreated. The worker attacked vigorously until the cuticle was 
