398 
Psyche 
[December 
The males lean backwards, pulling at each other and often 
anchoring themselves by grasping foliage. Eventually, both become 
freely suspended, held only by their clasping organs. They then 
direct rapid sweeping blows against their opponent (Fig. 1). The 
forelegs are used in a boxing manner. After a few seconds to several 
minutes, one of the antagonists releases his grip and the victor 
shortly regains the dorsal position. Once attachment of the second 
male to the female is accomplished, takeover attempts are often 
successful. In the 5 fights in which the original male was known, he 
was displaced 3 times. 
In D. veliei and D. covilleae, a spine is present on the mid femora 
of both sexes. Those of the male are enlarged and hooked. In D. 
covilleae combats, the opponent’s thorax is held in the joint of the 
mid tibia and femur. By flexing the legs, the spine is brought against 
the body, and it was once seen to puncture the integument, drawing 
blood. Spines used in defense by stick insects are invariably more 
highly developed in males (Lea 1916; Robinson 1968; Bedford 1975) 
possibly because of their significance in male fighting. 
Well-developed male clasping organs (as in Diapheromera spp.) 
are not universally present in the order. In reviewing the Australian 
Phasmatodea, Key (1970) found male cerci only occasionally modi- 
fied into claspers. Perhaps varied cereal design is due to differing 
probabilities of takeover. 
The mean male over female length ratio of a sample of 155 
phasmid species (approximately 8% of described species) is .727. 
The average male D. veliei is .922 of the mean female length. This is 
an unusually slight difference in body lengths (see Fig. 2), with 94% 
of the sample having relatively smaller males (D. covilleae has a 
similar male/ female ratio: .916). It might be generally expected that 
males would be smaller than females when fecundity is dependent 
on size. By spending less time in development or consuming less 
food, males take fewer risks in reaching maturity. Even tiny males in 
species with internal fertilization are capable of producing an 
adequate ejaculate. Given that the niches of the sexes are similar, the 
degree of sexual dimorphism is apt to result from a balance of 
reproductive pressures acting on the male. These forces might 
include maximizing female encounter rates (mobility, material 
reserves affecting life span), the ability to invest materially in the 
success of progeny, and maintaining copulations by aggression. 
