Abstract: Population densities can affect the strength and direction of sexual selection on male traits. Most studies (Andersson 1994) have found that larger male organisms have an advantage for mating independent of population densities. In male Bolitotherus cornutus, there exists an allometric relationship between horn length and elytra length. We used the female as the focus of our studies on how densities of long horn and short horn males affected access to females by concentrating on courtship behaviors by males toward the female. We found that courtship success and female-based aggression are density-dependent in both long-horn and short-horn males, but that exclusive male aggression is density-dependent only in long-horn males. We also found that short-horn courtship success is long-horn density-dependent.