400 
Psyche 
[December 
MALE/ FEMALE LENGTH RATIO 
Figure 2. Male length/ female length frequency distribution for the order Phas- 
matodea (generated from citations in materials section). Dots along the curve 
represent midpoints of categories spanning 5% on the male/ female length axis and 
the number of species occupying these categories. The dashed vertical line represents 
the position of D. veliei (.922), the solid vertical line the mean dimorphism of high 
density species (.814, see text). 
The positive relationship between copulatory success and size is 
well established for some polygynous vertebrates (citations in 
Trivers 1972). The great male bulk and armature of the dynastine 
scarab beetles are agonistic adaptations (Beebe 1944; Eberhard 
1977). Larger males of the bibionid fly Plecia nearctica are more 
often found copulating than smaller males (Thornhill 1976). Potter 
et al (1976) showed size to be a critical factor in the outcome of 
combats between male mites. 
In the 2 observed fights between male D. veliei of markedly 
disparate size, the larger won. Two males from the extremes of the 
size continuum were placed in 10 aquaria with single females and 
924 hours of coupling were recorded. Large males accounted for 608 
