io6 
Psyche 
[June 
been on the substrate where the beetle sprayed, but since shifting the 
beetle to a new position seemed in no way to increase its vulnerability, 
the repellent effect must have been due, in part at least, to secretion 
remaining on the beetle itself. One can demonstrate visually that this 
is the case, simply by causing a beetle to discharge, and then transfer- 
ring him onto indicator paper, moving him from place to place as 
the minutes go by (Plate io, fig. 5). At each locus the paper is seen 
to discolor, and even as late as fifteen minutes after discharge a posi- 
tive test is still obtainable. m-Cresol evidently dissipates rather slowly, 
which is to be expected in view of its low vapor pressure : extrapolation 
from values given in the International Critical Tables (1928) yields 
ca. O.i mm at 25°C. 
It follows from the preceding that a given Chlaenius, when under 
attack by ants (and ants are probably important natural enemies of 
many carabids), is not likely to be subjected to continuous assail and 
forced to deplete its secretion in a rapid sequence of discharges. 
Chlaenius, like so many other carabids, walks rapidly. Actual meas- 
urements made with two individuals released on a smooth horizontal 
surface, showed the rate of locomotion to range from 15 to 19 cm./s. 
(time was measured with a stopwatch; distance was determined by 
chalking a line behind the beetle as it scurried along, and then laying 
a string along the trail and measuring its length). In the ca. 10 min. 
of invulnerability that follows a discharge, a beetle is therefore free 
to walk about 100 m. before it is again subject to assail. Surely, this 
must suffice to outdistance many an arthropod predator, and in the 
case oi ants, even a dense swarm of them. Of course, it remains to 
be seen whether the repellent effectiveness of the secretion against 
Pogonomyrmex is a true indication of its defensive potential against 
other ants, and against arthropods in general. 
There is one other observation worth mentioning, concerning the 
defensive use of the beetle’s mandibles. It was repeatedly noticed 
during the early stages of an attack, before Chlaenius had been induced 
to spray, that an ant venturing to within range of the beetle’s 
mandibles was bitten. Although such ants did not seem to receive 
EXPLANATION OF PLATE 12 
Fig. 1. Abacion magnum (Loomis). 
Fig. 2. Abacion discharging white droplets of secretion in response to 
handling. 
Fig. 3. Isolated segment of Abacion, treated with KOH and consisting of 
cuticle alone, showing the two glands (G). 
Fig. 4. Excised gland of Abacion, seen in partly polarized light. Notice the 
strongly birefringent muscle (A) that controls the terminal cuticular valve 
of the efferent duct. 
