Anecdotal treatments of Darwin's (1871) concept of sexual selection have been frequent; quantitative evidence has been rare, however, requiring as it does demonstration of the operation of selection in nature, with regard to particular secondary sexual traits. Indeed, the measurement of any aspect of fitness in nature is notoriously complex and difficult. Conditions exist, however, which render feasible a direct approach to one component, mating success, in natural populations of certain species. (See, e.g., Mason, 1964; Mason, 1969; Thornhill, 1976; Davies and Halliday, 1977; Eanes et al., 1977; Scheiring, 1977; McCauley and Wade, 1978. This is made possible in certain insect species (notably beetles but members of other orders as well) because copulation is long-lasting in the field and very large numbers of mating pairs as well as unmated individuals can be collected and their characteristics compared. Nonmating fractions will, naturally, always contain some individuals with varying capabilities to mate. Differences between mating and nonmating fractions collected in this way will, therefore, be an underestimate of differences existing in the population. Many of the papers mentioned above demonstrate some correlation between mating success and the sizes of individuals; rarely is any other sort of characteristic considered, although certainly characteristics other than size must be relevant to mating success. For example, does color pattern sometimes influence an individual's success in mating? More particularly, what is the relationship between mating success and primary and secondary sexual characteristics? The current study deals with characteristics of various sorts, including characteristics which have clear sexual implications and so relate directly to sexual selection as conceived by Darwin.