64 
Psyche 
[September 
they do in certain millipedes and tenebrionid beetles that also dis- 
charge quinones (Eisner, 1961) — but rather are ejected forcibly as 
a spray. It is also apparent from the figures that the spray is not 
ejected in a fixed direction, but is actually aimed with considerable 
precision toward the particular region of the body subjected to stimu- 
lation. This finding, although new for earwigs, is by no means novel 
as it applies to arthropods in general : bombardier beetles, certain 
cockroaches, whipscorpions, and a variety of others, are all known to 
aim their spray (Eisner, 1958a, 1958b, 1961; Eisner et al., 1959; 
Eisner et al., 1961 ) . 
The mechanism by which the earwigs aim is intimately linked with 
the defensive use of their pincers, since by revolving the abdomen at 
its base while bringing the pincers toward the stimulus, the gland 
openings are automatically pointed in the proper direction. It is 
interesting in this context that the forceps seem to be used in pre- 
cedence to the glands. When a stimulus is applied, a secretory dis- 
charge usually does not follow at once. As a rule, the pincers are 
brought into action first, and then, only after their persistent use for 
several seconds has proven futile, is the spray finally ejected. When 
the stimulus applied is a more violent one, however, such as when 
the head or abdomen is pinched with hot broad-tipped forceps, or the 
animal simply seized between the fingers, the discharge may follow 
with little or no delay. In other arthropods with similar defensive 
glands, but lacking such auxiliary mechanical devices as the earwig’s 
pincers, even a slight traumatic disturbance usually elicits a prompt 
discharge (Eisner 1958a, 1958b; Eisner et al., 1959; Eisner et al., 
1961). 
Up to six consecutive discharges could be evoked from a single 
earwig, but usually they produced no more than four. The amount 
of secretion ejected decreases progressively, until finally there are 
produced on the paper no more than a few spots at close range. 
The earliest that an earwig with depleted glands was ever tested 
to check on the restoration of its secretory supply was after a period 
of five days: by this time it was again able to discharge three times. 
Explanation of Plate 7 
Figure 1. Earwig fastened to hook, in normal stance. 
Figure 2. Earwig having its right metathoracic leg pinched with forceps, 
responding b)' bringing its pincers to bear upon the forceps. 
Figure 3. Same as preceding, but the stimulus is applied to the right 
antenna. 
