jg 6 
Psyche 
[March 
seized in forceps. The initial contact of hindlegs and glands appeared 
at times to be deliberate rather than fortuitous. Thus, when glands 
were insufficiently everted to effect automatic contact with the hind- 
legs, the legs sometimes reached back toward the glands and brushed 
against them. Wiping of midlegs against hindlegs, and of forelegs 
against midlegs, quickly followed. In cases where the beetles had 
been placed on indicator paper, the legs left dark markings on the 
substrate as evidence of their contamination. Some experiments 
comparable to the preceding were also done with A. pustulosum, with 
essentially similar results. However, forcible gland eversion with 
spray ejection was never seen in this species. 
Scanning electronmicroscopic examination of the surface of everted 
glands of A. percatum revealed a covering of slender curved hairs 
(Fig. 9). Whether these are spaced closely enough to act as a mat- 
ting remains uncertain. But it is conceivable that they function in 
this capacity, providing perhaps for the maintenance of uniform 
secretory wetness over the surface of the glands when they are everted 
and for spontaneous re-spreading of secretion over areas wiped clean 
by defensive action of the glands. Dispensation of secretion onto 
target surfaces might also be facilitated by the hairs. 
Stridulatory Mechanism 
When seized or pinched, A. pustulosum produced a distinctly 
audible sound. The response took precedence over gland eversion, 
and could persist for seconds if the disturbance was sustained. Two 
serrate ridges on the last (visible) abdominal tergite (Figs. 10-13) 
are responsible for engendering the sound. By rhythmic downward 
deflection of the abdominal tip — a motion depicted in Figs. 10 and 
11 — the beetles scrape the ridges back and forth across the sharp 
overhanging elytral margins, thereby inducing a repetitive bi-syllabic 
chirp. Intensified stimulation eventually caused gland extrusion, 
which silenced the sound, since during gland eversion abdominal 
deflection is apparently precluded. A. percatum lacks the ridges and 
is soundless. 
Stridulatory mechanisms are common in insects, and have been 
repeatedly noted. In the leaf-cutting ant, Atta cehpalotes , which pro- 
duces sound by scraping a file in much the same manner as does 
Adelium, acoustical output and sound generation have been master- 
fully analyzed (Markl, 1968). Since this analysis is essentially 
applicable to Adelium, we will here describe only the properties of 
