1968] 
Barth — Behavior of Gromphadorhina 
125 
in Roth and Willis, i960). There is considerable size variation in 
the adults of this species, large males sometimes reaching a length 
of 8 to 10 cm. Males tend to be larger than females and differ 
from females in having antennae with many long laterally projecting 
sensory hairs, while the latter possess the simple filiform type of 
antennae characteristic of cockroaches. Males also differ from fe- 
males in that their pronotal shields are greatly thickened and pro- 
vided with a pair of large heavy knobs. 
Alarm Behavior and Aggressive Behavior of Males. 
The most notable features of the general behavior of this species 
are the aggressive behavior of the males and the production, by 
expulsion of air through the second pair of abdominal spiracles, of 
a loud hissing noise when alarmed. The former is briefly described 
below. Two males approaching each other while foraging^ raise their 
bodies considerably off the substratum, curving their abdomens up- 
wards at the tip. The rate of antennal waving or twitching increases 
markedly. When the antennae of the two come into contact they 
are twitched back and forth very rapidly and vigorously. Both 
animals then lower their foreparts so that their pronotal shields 
are directed towards the opponent. Rhythmic hissing may occur 
at this stage. Then they charge, their knobbed pronotal shields 
coming together frequently with an audible sound. They vigorously 
push each other back and forth, the winner being the one which can 
push his opponent backwards until it takes flight. Sometimes the 
victor slaps his abdomen vigorously against the substratum, and may 
turn and slap his abdomen against the opponent. A retreating animal 
may be vigorously chased for some distance by the victorious animal. 
The largest male of a group of males is the most frequent victor in 
these disputes and there is some evidence (Engelmann, pers. com.,) 
that dominance hierarchies among caged animals are set up in this 
way. 
Dumortier (1965) discusses the hissing behavior of a closely re- 
lated species, G. brunneri , and describes in some detail the mech- 
anism of sound production. He reports that in addition to its role 
in alarm behavior, males of G. brunneri also employ hissing in ag- 
gressive behavior. According to Dumortier the aggressive behavior 
of G. brun neri males (which seems to be very similar to that of 
G. portentosa males), appears in connection with territorial defense. 
Mating Behavior. 
There appear to be no previous accounts of the mating behavior 
of G. portentosa in the literature. The present description is based 
