PSYCHE 
Vol. 75 September, 1968 No. 3 
THE DEFENSIVE BEHAVIOR OF 
PTERINOXYLUS SPINULOSUS REDTENBACHER, 
A WINGED STICK INSECT 
FROM PANAMA ( PHASMATODEA) * 
By Michael H. Robinson 
Smithsonian Tropical Research Institute, 
P. O. Box 2072, Balboa, Canal Zone. 
At least two fundamental categories of anti-predator adaptations 
can usefully be recognized (Robinson 1968). There are those adap- 
tations which lower the probability of a predator initiating a prey 
capture attempt, either by concealing the presence of a potential prey 
(crypsis), or by advertizing its real or apparent unsuitability as a 
prey item (aposematism and pseudaposematism) . In the second cate- 
gory are those devices which lower the probability that a prey cap- 
ture attempt will be successful once it has been initiated. This 
category includes systems of active escape by flight, jumping or 
dropping and systems of predator deterrence by startle displays, 
bluffing displays, repugnatorial secretion and active counterattack. 
This present paper is one of a series on phasmid defensive behavior 
and describes anti-predator adaptations which belong to both the 
functional categories outlined above. The winged stick insect Pterin- 
oxylus spinulosus is of more than usual interest since it has a resting 
attitude which is considerably more complex than any so far described 
for a stick-mimicking phasmid. This involves special attitudes of the 
intermediate and posterior limbs in addition to the anterior limb 
attitude which is associated with stick-mimicry in this and other 
phasmids. Both sexes display as adults but there is strong sexual 
dimorphism in the type of display and that of the female sex includes 
a stridulatory component. Both the complex resting attitude and 
the dimorphism of the display raise questions of considerable evolu- 
tionary interest; these are discussed below (pages 202-205). 
The Neotropical phasmid genus Pterinoxylus is, according to Rehn 
( 1 957 ) ? a relatively rare one. P. spinulosus was described by Red- 
*Manuscript received by the editor May 13, 1968 
195 
