1958] 
Wilson — Chemical Release r 
45 
to the stimulus, the alarm behavior grows generally less 
intense, and the waves of expansion grow ever shorter 
(See figure 1). 
The Release of Alarm Behavior 
by the Mandibular Gland Secretion 
It has been noted repeatedly that purely mechanical 
stimulation of one worker by another is not ordinarily 
adequate to effect alarm behavior of significant intensity. 
Workers falling accidentally from the nest walls have 
been observed to push heavily against other workers with- 
out creating noticeable excitement. The same is true when 
injured workers occasionally manifest abnormally high 
locomotory activity for sustained periods and repeatedly 
bump against nestmates- Workers within the nest can 
also be pushed about lightly with clean glass rods, pro- 
viding the ants are allowed to adapt to the immobile rods 
for a short time beforehand. Two other kinds of stimuli 
have proven most effective in eliciting alarm behavior: 
sound, especially that transmitted through the solid medium 
of the nest walls, and alien chemical substances. 
The presence of a chemical releaser of alarm behavior 
was suspected when it was noted that greatly excited 
Pogonomyrmex badius workers discharge a highly volatile, 
pungently odorous substance. When workers of another 
species, Solenopsis saevissima (Fr. Smith), were allowed 
to invade a badius nest, the substance was discharged 
continuously for several hours and was associated with 
a state of high excitement among the badius workers. 
Dissections of anesthetized workers revealed that the 
substance is concentrated, perhaps exclusively, in the res- 
ervoir of the mandibular gland of the head 1 
In a majority of workers that have been removed care- 
1 The morphology of the mandibular gland of ants has been 
described by Janet (1898) and more recently by Whelden (1957a, 1957b). 
As shown by these authors, the gland reservoir lacks constrictor muscles, 
and it seems likely that contraction is achieved through an increase 
in the surrounding hemolymph pressure. The gland and its reservoir 
are best exposed by splitting the head sagittally and removing the 
pharynx and associated tissues. Direct removal of the mandible by 
extraction almost always results in the collapse of the gland reservoir 
and loss of its contents. 
